Patent Grant
8299345
The present invention relates to a tuning device for a musical instrument, such as a guitar.
A conventional tuning device for musical instruments, such as disclosed in U.S. Pat. No. 4,429,609 by Warrender, U.S. Pat. No. 4,457,203 by Schoenberg et al., U.S. Pat. No. 7,288,709 by Chiba and US 2006/0185499A1 by D'Addario et al., all hereby incorporated by reference, can measure one pitch frequency at a time and display the frequency deviation between the input signal and a target frequency. If a polyphonic signal, such as two pitch frequencies simultaneously, is fed to a conventional tuning device the display will typically be blank, indicating that no valid input was detected.
In many practical situations the musician does not hear the instrument while tuning, as this would be disturbing for an audience. Furthermore, the time to correct tuning of the instrument is often limited, as for instance in the break between songs in a performance. It is therefore important that the tuning device provides a user-friendly and appropriate output and works reliably and fast.
In order to tune an instrument like a guitar, which typically has six strings, each string must be plucked separately and the tuning must be adjusted until the deviation is sufficiently small.
In such a conventional tuning device verification of correct tuning requires that each string is plucked separately. This process is time-consuming.
Sometimes just one of six strings is out of tune, but in order to identify which string it is and subsequently correct the tuning each string must be checked. When using a conventional tuning device this checking process is of a serial nature, in that only one string at a time can be measured.
In many guitars adjusting the tuning of one string influences the tuning of the other strings. This is caused by the changed mechanical tension in the string being tuned, and therefore changed overall tension of the strings. As a guitar neck and body does posses some elasticity, tensioning one string will cause the tension of the other strings to be reduced slightly, due to bending of the neck and body, and thus potentially cause a need for re-tuning the other strings. A simultaneous display of the tuning of all six strings could be helpful when such a guitar is being tuned.
Some musical instrument tuners are generally applicable in that they have display means for indicating all 12 semitone names (from the chromatic scale). Such a tuner is commonly called “chromatic”. Notice that the pattern of 12 semitones repeats for each musical octave through the frequency (or pitch) range. In Western music the tone names are A, B, C, D, E, F, G plus an optional semi-tone step indicated by # or b.
Other musical instrument tuners are specialised for instance for guitar use, such that only the tone names corresponding to the nominal values of the six strings: E, A, D, G, B, E, can be shown.
In general, conventional tuning devices do not require any modifications to the musical instrument in order to be usable.
The problem of tuning a guitar can also be solved using automatic means. An element of such a system is a measurement part, which by using one method or another, measures the tuning of each string. Such systems may work only for a single string at a time, whereas others may work on all strings simultaneously.
One such automatic tuning system is described in U.S. Pat. No. 4,803,908 by Skinn et al., where the sound signal for each string is measured separately by means of a pick-up for each string. So apart from the motors, gears, etc. needed to adjust the tuning automatically, the guitar must also be equipped with a special pick-up system.
In U.S. Pat. No. 4,375,180 by Scholz is described a system for automatic tuning of a guitar where the measurement of frequency is based on a mechanical measurement of the tension of each string, compared to a reference. That system is also dependent on a modification to a standard guitar, even for just the measurement part.
Another tuning device, in which frequency deviations for more than one string at time can be measured and displayed, is disclosed in U.S. Pat. No. 6,066,790 by Freeland et al., hereby incorporated by reference. This system can use a single channel pick-up, common for all strings, for measurement of all strings simultaneously. Hereby some disadvantages of the conventional tuning devices are reduced. However, according to the disclosure of U.S. Pat. No. 6,066,790, the same display format is used whether one or several strings are played at a time. If just a single string is being tuned only a small part of the display is used for showing relevant information. Moreover, the tuner disclosed in U.S. Pat. No. 6,066,790 is fixed with regard to the e.g. six frequency bands that are tied to a certain instrument type, e.g. a guitar, and the display configuration. Hence, the tuner only provides useful information for strings that are within a limited range of their correct tuning. In other words, a chromatic tuner cannot be derived from the disclosure of U.S. Pat. No. 6,066,790.
It is an object of the present invention to provide a tuner that enables an unmodified guitar to be tuned easily by strumming/playing the strings simultaneously, and also facilitates precision tuning of individual strings.
It is an object of the present invention to provide a tuner with an improved visual output.
It is an object of the present invention to provide a tuner with an improved and more efficient use of the display area, such that a small and cost-effective display can be used.
The present invention relates to a musical instrument tuner comprising:
By means of the present invention musicians have been given the possibility to get an overview of the tuning of their polyphonic instrument by simply having their instrument sound its different tones simultaneously, i.e. polyphonically, and monitor a single reading on a musical instrument tuner according to the present invention.
In other words a guitarist, for example, may simply perform a single strum of all the strings simultaneously and watch the tuner's display to get an indication of the state of tuning. Compared with prior art tuners which allow for checking only one string at a time, the present invention drastically decreases the time and effort necessary to verify the tuning, e.g. between two songs in a live concert session.
When the musician has been provided with an overview of the state of tuning by means of the present invention, and should the musician not accept this state, the present invention further facilitates monophonic, e.g. single-string, tuning with a higher detection and/or display precision. Hence, e.g. being made aware of a somewhat off D-string from the polyphonic overview, the guitarist in a preferred embodiment of the present invention, simply plucks only the D-string to change the display mode, and preferably also the detection mode, to monophonic, where the same or another display zone provides higher level of detail about the tuning of this string.
The musical instrument tuner will be used on different kinds of input signal, such as guitar and bass guitar, or one string plucked at a time, or several. Depending on the kind of signal input the information which is presented on the display will be different, and in order to use the display in an optimum way with respect to readability of the information, the display mode changes in dependency of the kind of signal or information to display.
In particular, the resolution or level of detail that is utilized for providing information about a pitch frequency determined from the input signal may advantageously be increased to include the entire available display zone when this is the only or dominant information to show, while the resolution or level of detail has to be decreased for each pitch frequency when information about e.g. 6 pitch frequencies is to be displayed simultaneously with substantially equal weight. In other words the present invention provides a tuner that is able to better utilize the available display means by scaling the level of detail according to the kind of information that is currently displayed.
When tuning a musical instrument such as a guitar it is very advantageous to be able to view information about pitch frequencies or the tuning of several strummed strings simultaneously, and view information about the tuning of a single string at time, e.g. for fine tuning purposes. The view of information about all strummed strings is preferably provided in a polyphonic display mode and the view of information about the single string to be tuned is preferably provided in a mono polyphonic display mode having a higher resolution i.e. greater level of detail than what is provided in the polyphonic display mode.
Having a display enabling a first resolution and a second resolution higher than the first is very advantageous to the musician when the musician needs to fine tune one string of e.g. a guitar. The overview is provided in the first resolution and the pitch frequency information about the string which is to be fine tuned is provided in the second resolution which is high, thus enabling a high level of details when displaying this information and thereby making it easier for the musician to see when the string is perfectly tuned.
It should be noted that according to an embodiment of the invention the musical instrument tuner may be provided with a display that only allows for viewing one display mode at a time. Hence the musician may strum all strings and get an overview of the tuning of all strings in the polyphonic display mode and it is possible to notice if one or more strings are out of tune. In case a string needs to be tuned the musician may preferably select to only show information about that particular string in the display in a monophonic display mode. Since now only characteristics of one string instead of characteristics of six strings is to be displayed in the display the available resolution accordingly becomes about six times greater, facilitating a greater level of detail in the displaying of information about the single string.
According to an embodiment of the invention resolution should be understood as level of detail in which something is displayed e.g. the area or number of dots used per displayed pitch frequency in a dot kind of display. Hence displaying a pitch frequency in a high resolution requires more dots than displaying the same pitch frequency in a low resolution. Besides the number of 1 bit dots, e.g. using only 2 states (on and off) for light emitting diodes (LED) or liquid crystal display (LCD) pixels, further resolution may also be provided by other means which can be used for increasing the level of detail in which a characteristic is displayed. Further resolution may e.g. be provided by multi-color LEDs, by several on-states of the LED with different light intensities, by arranging for different symbols to light up to indicate a certain interpretation to use, e.g. that a factor is applied to the results, indicating the current octave, etc., or any combination of the above, possibly with other suitable visible or non-visible means.
Hence, although the present description for simplicity mostly considers the number of dots of a display zone when considering resolution, it is noted that all features which together enables and defines a certain level of detail to be conveyed to the user by the tuner in a certain mode, is within the scope of the present invention.
The displaying of information in a higher resolution may involve simply displaying a scaled version of substantially the same image. In this way a standard tuner view that resembles a classic, analogue needle instrument may be scaled to a higher resolution which allows for reproducing a narrower needle which in turn allows for a higher reading precision for the user. Alternatively, the displaying of information in a higher resolution may involve choosing a different image configuration for providing the same information, e.g. shifting from a low resolution needle view to a high resolution stroboscopic tuner view, or from a view with simply three dots or LEDs indicating too low, about right and too high, to e.g. a high resolution needle view. The high resolution mode may also provide for displaying further details than available in the low resolution mode, e.g. displaying numeric information about pitch or deviation from target pitch, information about reliability of the pitch information or the selected target pitch, tuning scheme, key, etc., in addition to an intuitively simple, visual view, e.g. a needle view, or it may allow for showing the same information in different ways simultaneously, e.g. a combination of a needle view and a stroboscopic view.
It should be noted that the musical instrument tuner may also sometimes be referred to as musical tuning device, tuning device or simply tuner in the present specification.
In an embodiment of the invention a polyphonic display mode and a monophonic display mode may be displayed at the same time or one at a time by the display.
It may be very advantageous to be able to view the monophonic display mode at the same time as the polyphonic display mode, i.e. both the high and low resolution views, because this facilitates that the musician at the same time has both an overview of all strings and a detailed view of one string to be fine tuned. The string to represent in the monophonic display mode in a situation where information of several strings are available may be determined in different ways, e.g. manually by the user, semi-automatically by the user by selecting a target tone to match, a key or a tuning scheme, or automatically as the string most out of tune, the string that is considered most important to be correctly tuned, the string whose tuning is currently changing the most because the user is in a process of tuning it, or the string may be selected according to any other way that suits a user of an instrument tuner.
In an embodiment of the invention a pitch frequency to be represented in a monophonic display mode is determined automatically.
It may be very advantageous that the musical instrument tuner automatically detects the pitch frequency to be displayed in the monophonic display mode. The basis for the automatic detection may e.g. be the tone which is most out of tune, the next tone in the line of tones, the one whose tuning changes the most because the user is in the process of tuning it, etc.
In an embodiment of the invention said multiple pitch frequencies of said polyphonic characteristic refer to predetermined target pitch frequencies.
The musical instrument tuner may advantageously compare the established pitch frequencies with predetermined target pitch frequencies e.g. to be able to determine the degree of deviation from the established pitch frequencies to the related target pitch frequencies or simply determine which tones the established pitch frequencies correspond to. The predetermined target pitch frequencies may be determined according to standard tunings of different instrument types, e.g. 6-stringed guitar, 4-stringed bass guitar, etc., according to user-defined tunings, or even according to the actually measured pitch frequencies e.g. such that the tuner compares each measured pitch frequency with e.g. the tone or semi-tone that comes closest.
In an embodiment of the invention said pitch frequency of said monophonic characteristic refers to a predetermined target pitch frequency.
The musical instrument tuner may advantageously compare the established pitch frequency with a predetermined target pitch frequency e.g. to be able to determine the degree of deviation from an established pitch frequency to the related target pitch frequency or simply determine which tone the established pitch frequency corresponds to. The predetermined target pitch frequency may be determined as described above with regard to polyphonic characteristics.
It should be noted that the display may also sometimes be referred to as an indicator in the present specification.
In an embodiment of the invention said monophonic display mode comprises a representation of a pitch frequency or a deviation from a target pitch frequency, and said polyphonic display mode comprises several representations of pitch frequencies or several deviations from one or more target pitch frequencies.
In order to get the best possible readability of the information in the display, the measurement for a single pitch frequency is presented in such a way that the user can focus on that single tone, whereas in the case of polyphonic input an overview is presented.
An easily readable presentation of the frequency deviation in an optimum way displays an overview when a multitude of strings are struck/plucked/played/strummed, and alternatively displays a high precision indication of the frequency deviation when a single string is plucked.
In an embodiment of the invention said target pitch frequency is determined automatically on the basis of said pitch frequency.
In an embodiment of the invention said display is arranged with a well-defined behaviour for use for input signals where said display modes are unsuitable.
In an embodiment of the invention said signal analyzer comprises a monophonic pitch detector and a polyphonic pitch detector.
The primary characteristic measured by a musical instrument tuner is the pitch frequency, especially the deviation from the reference or target pitch frequencies. When determining the pitch frequency of a tone, different measurement methods for monophonic and polyphonic signals are suitable. The pitch detection may be advantageously done in said signal analyzer of the tuner.
In an embodiment of the invention said input signal is a single channel audio signal.
It is a very advantageous aspect of the present invention that the musical instrument tuner can be used together with unmodified instruments, which normally only have a single audio channel common for all strings.
It should be noted that the input signal may also sometimes be referred to as audio signal.
In an embodiment of the invention the musical instrument tuner comprises an input signal conditioner.
In an embodiment of the invention said input signal conditioner comprises a hum filter.
In an embodiment of the invention said musical instrument tuner comprises a signal classifier for determining a signal class of the input signal from a group of classes at least comprising
By classifying the input signal to a musical instrument tuner into either a monophonic or polyphonic class the tuner can measure and display signal characteristics in an optimum way depending on the classification. This is in particular useful in an embodiment designed for only displaying one display mode at a time, as with such an embodiment the user would otherwise have to select a display mode manually.
This advantageous embodiment enables automatic changes between different display modes which facilitates user-friendly, reliable and accurate indication of either monophonic or polyphonic characteristics, and thus a conventional, unmodified guitar can be tuned easily by strumming/playing the strings simultaneously, or one string at a time as the user wishes, without requiring the user to change the display mode accordingly. The automatic signal classifier, also referred to as signal type classification means, may in an embodiment of the invention also enable automatic change between mono- and polydetection algorithms.
Hence, the present embodiment also provides a tuner with an improved visual output because it always can utilize the available display means to show as much usable information as possible about the input signal, because it actually knows, due to the classifier, how much information is usable. The tuner of the present invention shows sensible/usable information for most types of input signal, in particular monophonic and polyphonic signals.
A signal class is defined by certain properties that the input signal can have. Basically, input signals are according to the present invention classified as either belonging to a monophonic signal class, preferably defined by the property of containing a single pitch, or to a polyphonic signal class, preferably defined by the property of containing two or more pitches. It is noted, however, that more advanced embodiments of the present invention provides for further signal classes to be available, including variations of the generic monophonic and polyphonic signal classes, e.g. a guitar polyphonic signal class for signals having the property of containing between two and six pitches related to a conventional guitar tuning, and a bass polyphonic signal class for signals having the property of containing between two and four pitches related to a conventional 4-string bass tuning, or even a 6-string guitar polyphonic class as well as a 7-string guitar polyphonic class. The monophonic class could likewise be subdivided into a guitar monophonic class and a bass monophonic class, etc. Among other things the more detailed classification can be used to control the display, e.g. how many strings should be illustrated in a polyphonic mode, or to control the pitch detection and other analysis, e.g. the choice of signal analyzer algorithm or the use of a specific input signal conditioner, e.g. a pre-emphasis filter.
Also classification based on other properties than the number and value of pitches or in combination therewith, is within the scope of the present invention. For example, spectral features of the input signal, e.g. the spectral envelope, may be employed in combination with or instead of pitch information, in a classification distinguishing between, e.g. guitar or bass, and thereby automatically change between variants of the signal analyzer each of which can provide a more accurate, robust, or responsive analysis, for the particular signal class.
One of the variations of the monophonic and polyphonic signal classes is used in an embodiment of the invention where a polyphonic pitch detector is simply provided for both classifier and pitch detector for both polyphonic and monophonic signals. The classification is simply made on the basis of the output of the polyphonic pitch detector, but in this case it might not be reliable to classify two-or-more pitch signals as polyphonic signals. This is because a simple polyphonic pitch detector would often erroneously recognize activity in e.g. both the low-E, A and high-E bands of a guitar when just the low-E string is plucked due to the similarity of fundamentals and harmonics of these strings. A simple, though also non-optimal, measure to avoid erroneous classification of certain monophonic signals as belonging to a polyphonic signal class would be to define the monophonic signal class as all signals with apparently e.g. three or less pitches, or only signals with apparently e.g. three or less pitches having a harmonic relationship.
A tuner comprising a simple polyphonic pitch detector which in practice acts as a simple classifier as described above is thus considered within the scope of the present invention, as is a tuner comprising a simple monophonic pitch detector which in practice acts as a simple classifier by e.g. causing a polyphonic pitch detection to be carried out when the output from the monophonic pitch detector is unclear.
An advanced embodiment of the invention provides a set of polyphonic signal classes corresponding to different chord-types. A chord may consist of, for example, three pitches with certain frequency-relations to each other. As playing chords are typically a part of playing e.g. the guitar, this embodiment may allow an even more natural and effective tuning application, as the guitar then can be tuned while the musician is playing, provided the chord can be held long enough for the tuner to detect the pitches and determine if a string is out of tune. It is noted that the normal, simple tuning with loose strings is in principle just a special case of the chord tuning, as the normal tuning of a 6-string guitar corresponds to an Em11 chord.
In one embodiment of the above-mentioned chord tuning, the user programs in a suitable way, e.g. by use of a multi-switch or other input means of the user interface, the tuner to know the chord that is expected at the tuning time, e.g. instead of the Em11 chord for a conventional guitar tuning. This could be a specific chord that the musician uses regularly in his performance, or it could be an alternative loose-string tuning, such as e.g. an open A bar chord tuning.
In an alternative embodiment, the tuner detects the tones that are being played and if they make up a chord, it classifies the input signal as containing a certain chord and thus belongs to a specific chord class, as mentioned above. The tuner may then display the chord that is being played, and the correctness of the tuning according to the determined chord. If the musician has the skill and time available, he can tune any incorrectly tuned strings during the performance, even without good monitor conditions as has been required previously without the polyphonic chord tuner.
In yet an alternative embodiment, the classifier is arranged to analyze the harmonic relationship between pitches of the input signal, e.g. by comparing the distance in terms of semitones between the pitches. On this basis it can classify a signal as a certain type of chord.
In an embodiment of the invention said signal analyzer is coupled to or comprises said signal classifier and is arranged to determine said at least one characteristic in dependency of said signal class determined by said signal classifier.
The determination of characteristics of the input signal which are possible and relevant differ for monophonic and polyphonic input. Detection methods which are well suited for monophonic input signals often do not work on polyphonic input. Similarly, some measurement methods used on polyphonic signals do not offer sufficient range and precision for the typical use on a monophonic signal.
In an embodiment of the invention said signal classifier is arranged to determine said signal class by calculating a time domain function or a frequency domain transform of said input signal and depending on said function or transform performing pattern recognition.
Performing a suitable processing of the input signal, and apply pattern recognition is an advantageous method to determine signal classes.
In an embodiment of the invention a display mode to be displayed is determined on the basis of a setting of a user operable mode selector.
It may be very advantageous for the user of the musical instrument tuner to be able to decide how the musical instrument tuner displays the characteristics of the input signal originating from a musical instrument. Hence it is up to the user to decide whether to be provided with a detailed view of one pitch frequency or a less detailed view of more than one pitch frequencies. The mode selector may in an embodiment also be used to determine how the musical instrument tuner should interpret the input signal, or how it should be processed, e.g. choice of detection algorithm.
In an embodiment of the invention said mode selector comprises a manual switch operated by a user and wherein the manual switch is integrated in the housing.
It may be very advantageous to integrate the mode selector in the housing comprising the musical instrument tuner because then the musical instrument tuner becomes one compact unit which is easy to bring along for the user. Hence the musical instrument tuner may preferably be a standalone device but it should be noted that the musical instrument tuner may communicate with one or more displays not integrated in the musical instrument tuner. In a preferred embodiment of the invention, where the tuner is designed somewhat as a guitar pedal, the manual switch is preferably a foot switch. In alternative embodiments, e.g. a table-top embodiment, the manual switch may preferably be designed for operation by hand.
In an embodiment of the invention a common algorithm is comprised by the signal analyzer for establishing both polyphonic characteristics and monophonic characteristics from an input signal.
It may reduce need of components or costs of components when the same algorithm is used for establishing both monophonic characteristics and polyphonic characteristics. Furthermore it may simplify the construction of the musical instrument tuner.
According to an embodiment of the invention the algorithm may always try to establish polyphonic characteristics from the input signal but when it finds only one pitch frequency it might be because the input signal is a monophonic signal and the established characteristics can be displayed according to a monophonic display mode.
In an embodiment of the invention the signal analyzer comprises both a polyphonic algorithm for establishing polyphonic characteristics and a monophonic algorithm for establishing monophonic characteristics, and wherein the polyphonic algorithm and the monophonic algorithm are different.
In case the polyphonic algorithm is developed specifically to establish polyphonic characteristics and the monophonic algorithm is developed specifically to establish monophonic characteristics the individual algorithms may be optimized to that specific purpose. Thereby the processing speed may be increased, or the detail, resolution or number of results, etc., may be optimised to the particular aim.
Alternatively the part of the polyphonic algorithm and the monophonic algorithm establishing characteristics of the input signal may be the same but the part of the algorithm determining the display mode or preparing the visual output may differ. In a further embodiment, the polyphonic algorithm is used to establish initial characteristics regardless of the display mode or signal class, and then for the monophonic display mode, a monophonic algorithm is applied to refine the characteristics for the single pitch frequency.
In an embodiment of the invention said musical instrument tuner comprises a data storage.
It may be very advantageous to equip the musical instrument tuner with a data storage. A data storage enables the musician to store preferred musical instruments, user defined tuning profiles, tune log, mode (e.g. monophonic mode or polyphonic mode) of the input signal, desired display mode, etc. Depending on the information provided to the musical instrument tuner, the musical instrument tuner may be able to perform optimized calculations and thereby save time and energy/power.
In an embodiment of the invention said musical instrument tuner comprises an output module.
When the musical instrument tuner is equipped with an output module the musical instrument tuner may be located between the musical instrument and an amplifier, pedals, etc.
The output module may be implemented e.g. as a plug for a wire or a module for transmitting a wireless signal. Preferably the output module is capable of transmitting an output signal according to the same technology and by the same means as the input module is capable of receiving an input signal, so to allow for hassle free setup between existing components, e.g. between a guitar and a pedal array.
Moreover, the invention relates to a method for displaying tuning information by a musical instrument tuner, the musical instrument tuner comprising
The information which is presented on the display of e.g. a guitar tuner may according to the present invention be displayed differently in dependency of the amount or kind of information, or the user's preferences, etc. In order to use the display in an optimum way with respect to readability of the information, the display mode changes in dependency of the kind of signal or information to display.
In particular, the resolution or level of detail that is utilized for providing information about a pitch frequency determined from the input signal may advantageously be increased to include the entire available display zone when this is the only or dominant information to show, while the resolution or level of detail has to be decreased for each pitch frequency when information about e.g. 6 pitch frequencies is to be displayed simultaneously with substantially equal weight. In other words the present invention provides a tuner that is able to better utilize the available display means by scaling the level of detail according to the kind of information that is currently displayed.
It should be noted that according to different embodiments of the invention the musical instrument tuner may enable displaying the least two display modes simultaneously or one at a time.
According to an embodiment of the invention resolution should be understood as level of detail in which something is displayed e.g. the area or number of dots used per displayed pitch frequency in a dot kind of display. Hence displaying a pitch frequency in a high resolution requires more dots than displaying the same pitch frequency in a low resolution. It is noted that actually not only the number of available dots determines the available resolution, as further resolution may be provided by other means which can be used for increasing the level of detail in which a characteristic is displayed. Further resolution may e.g. be provided by multi-color LEDs, by several on-states of the LED with different light intensities, by arranging for different symbols to light up to indicate a certain interpretation to use, e.g. that a factor is applied to the results, indicating the current octave, etc., or any combination of the above, possibly with other suitable visible or non-visible means.
Hence, although the present description for simplicity mostly considers the number of dots of a display when considering resolution, it is noted that all features which together enables and defines a certain level of detail to be conveyed to the user by the tuner in a certain mode, is within the scope of the present invention.
The displaying of information in a higher resolution may involve simply displaying a scaled version of substantially the same image. In this way a standard tuner view that resembles a classic, analogue needle instrument may be scaled to a higher resolution which allows for reproducing a narrower needle which in turn allows for a higher reading precision for the user. Alternatively, the displaying of information in a higher resolution may involve choosing a different image configuration for providing the same information, e.g. shifting from a low resolution needle view to a high resolution stroboscopic tuner view, or from a view with simply three dots or LEDs indicating too low, about right and too high, to e.g. a high resolution needle view. The high resolution mode may also provide for displaying further details than available in the low resolution mode, e.g. displaying numeric information about pitch or deviation from target pitch, information about reliability of the pitch information or the selected target pitch, tuning scheme, key, etc., in addition to a pedagogic, visual view, e.g. a needle view, or it may allow for showing the same information in different ways simultaneously, e.g. a combination of a needle view and a stroboscopic view.
Moreover the invention relates to a computer program product comprising a computer readable medium having control logic stored therein for causing a computer to determine and display a characteristic of a musical instrument, the control logic comprising:
It is noted that software products delivered by e.g. network, e.g. via the Internet or by wireless means are also considered comprising a computer readable medium with the instructions stored therein, and are therefore within the scope of the present invention.
The present invention further relates to a musical instrument tuner comprising an input module and a signal analyzer, the input module receiving an input signal from a musical instrument and the signal analyzer determining at least two characteristics of said input signal,
the at least two characteristics comprising a monophonic characteristic comprising a representation of a pitch frequency and a polyphonic characteristic comprising a representation of multiple pitch frequencies,
wherein the pitch frequency of the monophonic characteristic is determined with a higher precision than each of a majority of the multiple pitch frequencies of the polyphonic characteristic.
When in practice the resources available for a tuner implementation are limited, e.g. with regard to processor speed or battery consumption, it is highly advantageous to have the detection in polyphonic mode to use less than e.g. a factor 6 plus overhead of the resources used to determine a single pitch frequency in monophonic mode. For instance, this facilitates table-top or pedal applications where the monophonic mode can utilize e.g. 6 times as many resources for determining a single pitch frequency with an extreme precision or speed, or it facilitates extremely small pocket tuners or built-in tuners where processor and battery power is limited and possibly even non-replaceable, as the pitch frequency determination in polyphonic mode can be reduced to collectively utilize the resources that are used to obtain a decent representation of a single pitch frequency in monophonic mode.
The invention will in the following be described with reference to the drawings where
The following definitions apply in the context of this document:
simultaneous display: a display of multiple images which appear to the human eye to be presented concurrently although they may actually be presented sequentially at a speed exceeding the eye's response;
real time: a time sufficiently close to the occurrence of an event as to be indistinguishable by a human observer from the actual time of the occurrence;
pitch frequency: a frequency associated with a pitch perceived from a sound, e.g. 261.626 Hz for the pitch C corresponding to the “middle C” on a piano with well-tempered tuning; a sound or corresponding audio signal may comprise several pitch frequencies, e.g. if generated by playing a chord;
target pitch frequency: a desired pitch frequency to which an instrument is to be tuned;
cents: a measure of frequency in which 100 cents equal one semitone, i.e. 1200 cents equal one octave;
frequency indicators: numbers and symbols representing either absolute or relative, or both, values of frequency (for example, a frequency displayed as a note and an offset in cents); and
wherein the terms frequency and period are regarded as equally unambiguous measures of frequency.
The housing H protects the components forming the musical instrument tuner MIT and because of the housing H the musical instrument tuner MIT is portable and at least to some extent protected against collisions and operatable e.g. by the foot of a user.
The input module IM enables the musical instrument tuner MIT to receive input signals from musical instruments (not illustrated). A musical instrument may e.g. be a stringed instrument such as a guitar, bass guitar, etc. or non-stringed instruments. The input signal may be received from a wire connecting the musical instrument to the musical instrument tuner MIT, wireless e.g. in form of a Bluetooth signal or received by a microphone. Both wired and wireless connections may be network configurations of any suitable kind or simple direct, dedicated connections. The input signal may either be a digital signal or an analogue signal.
It should be noted that the input module IM may also facilitate upload or download of data from a computer, the internet, etc. Hence in relation hereto the input module IM may be understood as an input interface for bidirectional data communication. Such data communication may be facilitated by an USB or other universal data communication standards.
In an embodiment of the invention the input module of the musical instrument tuner MIT comprises an USB port, or alternatively a network connection, a bus connection or any other suitable communication interface, and by use of this the user is able to upload data to or from the musical instrument tuner MIT. This may facilitate updating firmware, change sensitivity, change range of frequencies to be displayed, update program code, turn off or adjust features to obtain longer battery life, upload user defined profiles, etc.
The power supply input PSI supplies the musical instrument tuner MIT with power. Power may originate from a high voltage plug and then appropriately transformed to a low voltage determined by the components of the musical instrument tuner MIT by the power supply input PSI. Alternatively the power supply input PSI may comprise or be connectable to a battery pack e.g. a rechargeable battery pack. It should be noted that the power supply input PSI may simply be a socket for allowing connection to an external power supply.
The signal analyser SA performs calculations based on the input signal. The signal analyser SA may comprise a data processor. The data processor may e.g. be a digital signal processor, a central processing unit, a programmable gate array, or any other standard or custom processor or logic unit, and may operate based on an algorithm/algorithms depending on the type of input signal or display mode as described below. The program code and any temporary or permanent data executed and used by the data processor may be stored in suitable data storage, e.g. flash memory or RAM, from where it can be accessed by the data processor.
The user interface UI enables a user to interact with the musical instrument tuner MIT. The embodiment of the musical instrument tuner MIT illustrated on
It should be noted that a plurality of different functionalities may be facilitated by one or more multi switches MSW such as user profiles, thresholds, display modes, etc.
Furthermore it should be mentioned that often the display D would also be included in a reference to user interface UI.
The display D enables the music instrument tuner MIT to present information related to the input signal. The display D is preferably a display for visual presentation of information but may also be a speaker for audible presentation or motor or the like for mechanical presentation e.g. in form of vibrations.
The display D refers to the providing of information of an input signal e.g. to the user of the musical instrument tuner. A display D includes one or more display units DU and may e.g. use light, sound, vibrations etc. when providing information to the user. The musical instrument tuner MIT may provide information to e.g. a user and an assistant at the same time even if the user and the assistant is physically not located at the same location.
The display unit DU refers to the hardware which physically provide information of an input signal e.g. to the user of the musical instrument tuner MIT. Hence a display unit DU may e.g. be a single LED or pixel, LED display, LCD display, segmented display, speaker, etc. A musical instrument tuner MIT may be connected to or provide information to one or more display unit DU at the same time and these one or more display units DU may be located at any appropriate location e.g. in or as part of the housing H of the musical instrument tuner MIT, on the musical instrument, at a sound board, on a portable device, etc. Hence it is possible to display the same information at the same time via different display units DU e.g. to the user of the musical instrument tuner and to his technical assistant.
The display zone DZ refers to the part of a display unit DU displaying information to the use or forming the information which thereby is provided to e.g. the user. A display unit DU may comprise one or more display DZ zones hence a display zone DZ may e.g. be one or more pixels, one or more LEDs, a segmented display, a LCD or part of a LCD display, etc.
The display mode refers to the mode in which the information or characteristics of the input signal is provided e.g. to the user. The group of display modes may e.g. comprise start-up display mode, default display mode, fault display mode, configuration display mode, different kinds of monophonic display modes such as e.g. stroboscopic display mode and needle display mode, polyphonic display mode etc. A display mode is preferably displayed e.g. to the user in a display zone DZ, hence the more display zones DZ the more display modes may be displayed at the same time.
It should be mentioned that the musical instrument tuner is capable of displaying more the one display mode at the same time.
According to an embodiment of the invention the first and a second resolution should be understood as level of details in which a pitch frequency is displayed. Hence when it is stated that a pitch frequency in the monophonic display mode is displayed in a first resolution higher than the second resolution in which the same pitch frequency may be displayed in the polyphonic display mode it should be understood that the level of details are higher in the first resolution than in the second resolution.
The following is an example of use of a musical instrument MIT tuner illustrated in
The selection of the string to be tuned may be performed automatically e.g. the musical instrument tuner may present the string which is most out of tune in the monophonic display mode on the display D.
Alternatively the musician may manually inform the musical instrument tuner which string is to be tuned and thereby be illustrated in monophonic display mode on the display D. The musician may do this by activating one of the multi switches MSW1 or MSW2.
Yet another alternative could be a combination where the musician starts to tune a string after strumming all strings. The musical instrument tuner detects which string the musician is tuning by comparing the established characteristics from the first strum of all strings with the established characteristic of the string the musician has started to tune. The musical instrument tuner MIT is then providing information of this string in monophonic display mode on the display D.
No matter which of the above mentioned methods (or further not mentioned methods of choosing a string to be tuned) for choosing a string to be tuned, the chosen string is displayed in a monophonic display mode having a second resolution different from the first solution in which all strummed strings were displayed in a polyphonic display mode. In the embodiment illustrated on
Because of the fact that the same display zone is used to display both the monophonic display mode and the polyphonic display mode the resolution or number of pixels available e.g. per pitch frequency is about six times greater in the monophonic display mode than in the polyphonic display mode. This is facilitating a greater level of detail of the pitch frequency displayed in monophonic display mode which is making fine tuning of pitch frequencies related to e.g. strings of a guitar easier.
When one string is tuned the musician may shift to polyphonic display mode again to see if other strings needs fine tuning.
It should be noted that it is possible for the musician in an embodiment of the invention to predetermine an error threshold which when the pitch frequency to be tuned becomes closer to the target pitch frequency than the predetermined threshold, the musical instrument tuner MIT automatically switches back to polyphonic display mode.
Having more than one display unit DU enables the musician to get an overview of the tuning of all strummed strings at the same time as a detailed view of one single string is available.
In
The effect of this is that by the polyphonic display mode the musician may create an overview of all six strings while the musician at the same time by the monophonic display mode may be provided with a detailed overview of one string, preferably the string to be tuned.
In an embodiment where the display allows for displaying both a polyphonic display mode and a monophonic display mode at the same time, i.e. in different display zones, the physical resolution, technology and configuration for the different display zones may differ, and each be designed for optimal display of the respective display mode. Alternatively, the different display modes may obviously, as in an embodiment with only one display zone, be displayed by corresponding display resolution, technology and configuration, and even be displayed by a single physical display unit which is just virtually divided into two display zones.
It should be noted that what is displayed to the user is a representation of the established characteristics including a representation of one or more pitch frequencies from the input signal. How the established characteristics including a representation of one or more pitch frequencies is displayed depends on the type of display hence it may be representation by one or more pixels, diodes, segments, colours, sounds, etc. This is equal to the representation of the predetermined target pitch frequency which may also be represented depending on type of display hence it may be representation by one or more pixels, diodes, segments, colours, sounds, etc
Furthermore it should be mentioned that e.g. in the monophonic mode MM the displayed characteristic including a representation of a pitch frequency may be displayed relative to e.g. a target pitch frequency e.g. as a distance from the target pitch frequency.
Display Part
Overview
The display part of the tuner consists of some display rendering means DRM to control which lights, pixels, light emitting diodes etc., should be lit, and how much. The display rendering means is typically implemented in a microprocessor. For the actual presentation to the user some physical display means DM is used. Many suitable technologies for building displays exist, for example liquid crystal displays (LCD), light emitting diodes (LED), and organic LED (OLED).
LCD and OLED displays are often arranged as a high resolution dot-matrix, having thousands of display elements. For more cost-effective products, a custom LCD with a few hundred display elements may be used. Alternatively, a number of discrete LEDs may be used, typically from about 10 to about 100, but even as few as 1-3 diodes may be used according to a simple display embodiment of the present invention.
The display means is connected to the display rendering means typically within the same enclosure. There may however be a physical separation between the measurement and the display parts of the tuner. Alternatively there may be a separation between the display rendering means and the display means. Between the two parts the connection may be a simple cable or a network (wired or wireless), or some other suitable connection.
In a first embodiment of the invention a display mode is structured into two areas, see
The TDD1 is preferably used also for presentation in textual form of information regarding the settings of the tuning device. Such settings may include the frequency of the reference tone A, normally 440 Hz, but settable to slightly deviating values such as between 435 and 445 Hz.
Due to the large sensitivity of the eye to angular movements, compared to linear movements, it is advantageous to arrange display contents or elements in such a way that the tuning indicator “needle” (pattern of active display elements) changes its angle as well as position when the frequency deviation changes.
If a polyphonic signal is input to the tuning device the display changes appearance in order to be better suited for indicating the result of the polyphonic pitch measurement.
If for reasons of cost or space a display mode configuration like in
A small tuning deviation may be rendered as in
If a polyphonic signal is input to the tuning device also the simpler display changes appearance in order to be better suited for indicating the result of the polyphonic pitch measurement.
One way of indicating that a string is not being played is to blank the indicator for that particular string. This is illustrated in
An alternative embodiment of a simple display mode configuration is shown in
Due to the limitations of the very simple tuner display the pitch measurement results for all six strings cannot be displayed simultaneously. In the case where all six strings are in tune it is simple to display.
In case one or more strings are out of tune the very simple tuner display may show the name and deviation of that string which is in the strongest need of correction. When that string has been tuned into place the next string in need of tuning correction (if any) is displayed.
Sensible Display Information for Most Types of Input
It is an object of the present invention that the display, whether complex or simple, shows sensible and usable information for most types of input signal.
In particular, when the input signal is monophonic, the display DM shows the tone name (chroma) which most closely corresponds to the pitch of the input signal, and a measurement of the accuracy of the tuning is presented.
Alternatively, when an input signal consists of the signal from two or more strings, the display will indicate whether the input frequencies correspond to the desired values, and if not, the magnitude and direction of the deviation.
In the case that all of the expected input frequencies for six strings are present and in tune the display may present an extra indication, e.g. by turning on a green indicator. On the other hand, if one or more of the input frequencies are out of tune, even a very simple display can indicate the name of the note corresponding to the string which is mistuned by the largest amount, and the direction and possibly the degree of the frequency deviation.
Automatic Change of Display Mode for Monophonic and Polyphonic Input
It is an object of the present invention that it is easy and fast to use, and at the same time reliable in its measurements and display. Due to the constraints often present in real devices, a limited display will be available, and the challenge is to make the best use of it. The ability to change between different renderings for monophonic and polyphonic input signals is a very important aspect of utilising the display in an efficient way. Another aspect is of more practical nature, namely that the rendering mode, and possibly the measurement mode, changes automatically depending on the type of input. If the user needs to press a footswitch or similar to change between modes, when playing a single string or all of them, chances are that this switch will be in the wrong position so often that the availability of two measurement and display modes will tend to be more disturbing than helpful.
Nevertheless it might still be advantageous to be able to manually switch display mode, resolution of the display, physical display means such as displays based on different technologies or different location, etc. Being able to switch manually enables the musician to choose to get a specific information displayed or information of current importance displayed. This could be displayed instead of other information, together with other information on the same display or at further display.
A particularly advantageous embodiment of the invention therefore comprises means to change display mode automatically depending on whether the input signal consist of the signal from a single string or from two or more strings.
Automatic Change Between Guitar and Bass in Polyphonic Mode
As described below, the differences between guitars and bass guitars makes it desirable to be able to distinguish between the two for pitch detection purposes.
As the four middle strings of a six-string bass guitar as described below correspond to the four lowest strings on a guitar, but one octave lower, different labelling on the display for the polyphonic tuner may therefore be needed. In an embodiment of the present invention, this display change is made automatically, based on the characteristics of the measured input signal as described above.
A particularly advantageous embodiment of the invention therefore comprises means to change detection and display mode automatically depending on whether the input signal consist of the signal from a guitar or from a bass.
Alternative Measurement and Display Mode
In addition to said needle mode, a stroboscopic measurement and indication mode is advantageous, especially when the display mode changes automatically between polyphonic (needle-type) mode and monophonic strobe mode. The stroboscopic mode is very well suited to perform fine adjustments to the tuning of the instrument, whereas the needle mode is typically better suited for a quick indication of the state of the tuning—either in monophonic or polyphonic mode.
The stroboscopic measurement mode in the present invention emulates in the digital domain the classic technique described in U.S. Pat. No. 2,806,953 by Krauss and U.S. Pat. No. 3,952,625 by Peterson, which use a rotating disc together with a flashing light to tune a musical instrument. Also in U.S. Pat. No. 4,589,324 by Aronstein and in U.S. Pat. No. 5,777,248 by Campbell are described tuners based on the stroboscopic principle. All of these are hereby incorporated by reference.
Whether the stroboscopic tuner is implemented using electro-mechanical or digital means, the principle of indication is the same: When the input signal has a pitch frequency corresponding to the target pitch frequency the pattern on the disc or on the display appears to be stationary. If the pitch frequency of the input signal is below the target pitch frequency, the pattern appears to rotate in one direction, and if the pitch frequency is above the target pitch frequency the pattern appears to rotate in the opposite direction.
The digital implementation of the stroboscopic principle in the present invention consists of an input signal buffer and an interpolation means. The input buffer contains at least one, but preferably at least two, periods of the input signal, and is updated in real time with new input.
The interpolation means is synchronised to a target pitch frequency. This target frequency corresponds to the semitone closest to the pitch frequency. The monophonic tuner described above is used to determine the target pitch frequency. A number of samples corresponding to the number of display elements used for the stroboscopic display is sampled from the input buffer, at equally spaced time instances, such that one or two periods of the target pitch frequency can be represented by the samples.
In
If the pitch frequency of the input signal is below the target pitch frequency, the pattern appears to move to the left (or right), and if the pitch frequency is above the target pitch frequency the pattern appears to move in the opposite direction. The speed of the movement is proportional to the frequency deviation between the pitch frequency and the target pitch frequency. With a stroboscopic tuner as in the present invention it is possible to see very small frequency deviations in real time, and it is therefore a very good tuning aid.
In the display rendering means light intensity is used in this way for the stroboscopic display mode: Bright for positive instantaneous input signal value and dim for negative instantaneous input signal value, or vice versa.
A particularly advantageous embodiment of the invention comprises a stroboscopic measurement and display mode.
Another Alternative Display Mode
The same underlying mechanism which is used in the stroboscopic tuner can be used for a synchronised display of the input waveform, see
The target pitch frequency is, similarly as in the stroboscopic tuner, the semitone frequency being closest to the pitch frequency.
The three diodes may e.g. in a monophonic mode indicate flat, tuned and sharp, respectively, and in a polyphonic mode all light up in green if all the strummed strings are tuned, otherwise light up in red to indicate that one or more strings are off, possibly with the number of red diodes indicating how far off. Thereby the monophonic characteristics and polyphonic characteristics can be displayed with different resolution. Several other ways of arranging both monophonic and polyphonic display modes by using a small number of diodes, e.g. 1-3, are suitable and within the scope of the present invention, as e.g. indicated above with reference to
A musical instrument tuner MIT as illustrated in
For musical instrument tuner MIT embodiments that are small in size e.g. as small as the size of a plectrum, the accuracy, precision, display, calculation speed, number of algorithms, etc. may be decreased. The decrease in performance may e.g. be related to small data processors or the wish to reduce power consumption to extend battery life.
The musical instrument tuner MIT illustrated on
It should be mentioned that if the musical instrument tuner MIT is attached to the instrument, e.g. as a clip-on model or a built-in model, the musical instrument tuner MIT may comprise a motion sensor of any kind which may be used to detect if the guitar is in use and thereby determine if the musical instrument tuner should be put in standby to save energy.
In case the musical instrument tuner MIT is so small in size that it is not physically possible to implement a plug, the input module IM may be e.g. a microphone or a vibration detector, e.g. an accelerometer, for detecting signals from the instrument tuner, either through the air or via the instrument components.
The display D of such small musical instrument tuner MIT (or the other embodiments of musical instrument MIT tuners as described in this document) may be limited to one or more pixels or light emitting diodes, etc. depending on the desired display form. When only e.g. one diode is used this diode may use different colours, blinking, etc. to indicate mode of the input signal, if one or more strings are tuned, etc.
In the situation where the display D only comprises one diode, the musical instrument tuner may interpret an input signal e.g. from a guitar where all strings are strummed as a polyphonic input signal and by means of the one diode communicate whether or not the strings are sufficiently tuned. If the strings are not sufficiently tuned the musician may need to tune one string at the time and between tuning the individual strings, strum all strings to see if the result of the tuning is satisfying.
Similar when only one string is strummed, the musical instrument tuner MIT may interpret the input signal e.g. from a guitar as a monophonic input signal and by means of the one diode communicate whether or not the strummed string is sufficiently tuned.
It should be remembered that the embodiments illustrated in
Block Diagram of the Tuner
Refer to
The monophonic pitch detector MPD determines, if possible, the pitch period of the input signal and presents the determined period, frequency, or deviation from a target pitch frequency, on the output of the block. The target pitch frequency corresponds to the semitone closest to the determined pitch frequency, and is preferably determined by the monophonic pitch detector. If the input signal is not monophonic in nature the MPD may still deliver a result but it may not be a valid pitch period.
The polyphonic pitch detector PPD determines the pitch period of up to six partials which are present in the input signal simultaneously. These six partials are selected such that they can be used to selectively determine the pitch period for each of the six strings of the guitar. The polyphonic pitch detector PPD presents on its output the determined pitch period times, frequencies, or deviations from target frequencies or period times. The number of partials is preferably chosen according to the type of instruments the tuner is intended for, e.g. 6 partials for guitar type instruments with no more than 6 strings. Evidently, embodiments with other numbers of partials suitable for other instrument types are within the scope of the present invention.
The signal type classification means analyses the character of the input signal to identify whether it is of monophonic or polyphonic nature. If the input signal is of monophonic nature the display rendering means DRM renders the single determined pitch deviation in such a way that it is easy to read and has a high accuracy. If the input signal is polyphonic in nature the display rendering means DRM renders the multiple determined pitch deviations in such a way that a good overview of the tuning accuracy of all strings is achieved. The rendered pattern of display information is presented physically by the display means DM. If the input signal is neither a valid monophonic signal nor a valid polyphonic signal, for example white noise, the DRM will render a suitable indication, which may be to blank the display, or show the word “error”, or similar.
Sometimes the signal type classification means is also referred to as signal mode selector.
In some embodiments of the invention a signal mode selector may either be located as part of the input conditioning means, as part of the functional units preferably as part of the signal type classification means or as part of the display rendering means. The signal mode selector may be implemented either as an automatic selector such as a signal classifier or as a manually operatable switch such as a mode selector MS.
It should be noted that in a very simple form the mode selector or signal classifier may be implemented as a monophonic tuner, which when receiving a polyphonic input signal, outputs an indication of an error or simply blank—no output, which subsequent algorithms interpret as the existence of a polyphonic input signal.
Furthermore it should be noted that even the user may function as a mode selector or signal classifier by, in manual embodiments, choosing the desired mode or, in automatic embodiments, strum one string when monophonic mode is desired and more than one string when polyphonic mode is desired.
In some embodiments of the invention the functional blocks in the block diagram may be arranged in a different way, such that for example one block implements two or more of the tasks described. It is also possible in some embodiments of the invention that the functional blocks are connected in another sequence as long as the overall function is maintained.
The tuner is provided with power from a power supply input (not illustrated), which may be a battery or connectors connecting a battery to the musical instrument tuner, a socket adapted to a plug from an external power supply, a motion sensor or solar panel converting movements or light, respectively, to energy, etc.
The tuner may receive input via an input module or input interface enabling bidirectional data communication. Such data communication may be facilitated by an USB or other universal data communication standards.
In an embodiment of the invention the input module of the musical instrument tuner MIT comprises an USB port, or alternatively a network connection, a bus connection or any other suitable communication interface, and by use of this the user is able to upload data to or from the musical instrument tuner MIT. This may facilitate updating firmware, change sensitivity, change range of frequencies to be displayed, update software, turn off or adjust features to obtain longer battery life, upload user defined profiles, etc.
Detection Part
Monophonic Pitch Detection
The basic pitch determining function which all tuners must provide is the monophonic mode. It is typically used when a new string is mounted, and when a wide range and/or a high precision adjustment is required. In a preferred embodiment of the present invention the monophonic pitch detector has a wide frequency range, in the order of 7 octaves, such that it is able to determine pitch frequencies of all common musical instruments without changing settings. Several methods for determining the pitch frequency of a monophonic signal exist, such as for example:
The choice of method depends on both its accuracy, robustness and computational complexity. Furthermore, when choosing a pitch detection method it must be taken into account that different platforms, such as logic circuits, microprocessors and signal processors, exhibit different strengths and weaknesses, and that the optimum choice is therefore very dependent on the platform.
Some of the time domain methods are very simple and based on a binary sequence representing basically just the sign of the signal, two levels. Such methods can be implemented using simple circuits. The most simple is probably to determine the time distance between sign changes, equivalent to the zero crossing rate. A more advanced and robust binary time domain method is described in U.S. Pat. No. 4,429,609 by Warrender, in which a method of determining correlation between direct and delayed binary representations of input is used, hereby incorporated by reference.
Having a more precise signal representation, using more than two levels, enables the use of the more precise autocorrelation and average difference functions. A more capable computational platform is needed for these than for the methods using the binary sequence.
The frequency-domain methods such as the Fourier transform are also capable of very precise determination, at the cost of a relatively high computational complexity.
Any of these or any other pitch detection methods can be used as basic pitch frequency determining method in the present invention.
In a preferred embodiment of the present invention the ASDF function is used for mono-phonic pitch frequency determination.
Polyphonic Pitch Detection
Determining individual pitch frequencies in a complex audio signal can be challenging, and sometimes it is not possible to distinguish signals from different strings due to overlapping spectral contents. The standard tuning of a six-string guitar does allow an individual measurement of the six strings to be made, however, as also demonstrated in U.S. Pat. No. 6,066,790. Using the fundamental frequencies of the six strings is not necessarily the optimum choice due to the coincidence of harmonic partials from different strings. It must be remembered that for example on an electric guitar the fundamental is not necessarily the strongest partial in the signal from a string. The levels of the individual partials are very much dependent on the distance from the bridge to the magnetic pick-up.
One method to separate the partials from the six strings is to use a set of bandpass filters, one for each string, followed by a set of monophonic pitch detectors, such as described in the previous section. The center frequencies of the bandpass filters will be tuned to the desired target pitch frequencies of the strings, e.g. 5 or 4 semitones apart for a standard guitar tuning.
Another method for determining the frequencies of the individual partials is to use a Fourier transform on the, preferably conditioned, input signal containing all of the partials for all strings simultaneously. A single Fourier transform can then be used to find the desired pitch information for all six strings.
In a preferred embodiment of the present invention the polyphonic pitch detection consists of a set of bandpass filters followed by a set of monophonic pitch detectors. Having a polyphonic pitch detector and corresponding display with a simultaneous overview of all strings available makes it much easier for the user to compensate for the soft neck of many guitars and to tune floating bridge guitars, such that the undesired interaction between the tuning of the individual strings is less disturbing.
Regardless of which method is used to separate the signals from the individual strings, a limitation is inherent in the polyphonic pitch detection: As the polyphonic pitch detector has no way of knowing whether a set of harmonic partials of some fundamental frequency belongs to one string or another, it must assume that a certain frequency range around the nominal frequency of each string belongs to that particular string. It is thus possible, when a string is very much out of tune, that the measurement result is shown in the tuning indicator for the wrong string. For this reason it is important to have a wide frequency range monophonic tuner readily available in addition to the polyphonic tuner.
Distinguishing between input signals of monophonic and polyphonic nature In practical use, the most appropriate operating and display mode of the tuning device changes between polyphonic and monophonic mode. This change is motivated by automatic detection of the different strengths of the two modes.
Alternatively the change can be made manually e.g. by activating a switch on the tuning device, musical instrument, foot pedal, wire, etc.
Having to change mode manually, such as by pressing a footswitch, is inconvenient, however, as experience shows that in equipment with several operating modes, the one wanted is very often not the one currently set. It is therefore desirable that the tuner automatically senses the nature of the input signal and changes operating and display modes accordingly.
The nature of the input signal may in the context of the present invention be either monophonic (for a single string played) or polyphonic (when two or more strings are played). An advantageous part of the present invention is a classification means which senses whether the signal is monophonic or polyphonic.
In far most situations information to be displayed is determined automatic by the classification means. But situations might occur where it would be advantageous for the musician to overrule the automatic selected information and be able to perform a manually selection of information to be displayed. Such situation could occur when a musician plays two or more strings and the classification means senses and displays the tones in polyphonic mode. From this overview of e.g. six strings maybe only one string is out of tune or maybe the musician want to check one specific string in more details. In this situation it would be advantageous for the musician to be able to manually change the displayed information to get information of the specific string displayed. In case only one string is played it is still possible for the musician to choose to display that string manually, but often it might be preferred that the tuning device automatically takes that decision.
The information of the specific string may be displayed by means of the available display means. In the situation where the tuning device only comprises one display this display may be utilized for displaying the information of the specific string. Alternatively the display may be divided in sections where one section may continue to display information of more than one string in polyphonic mode, a second section may display a separate sting, a third section may display additional information, etc.
In the situation where the tuning device uses two or more physical displays a first display may be utilized for displaying the polyphonic mode and a second display may be utilized for displaying the separate sting e.g. in a stroboscopic mode for obtaining a higher precision of the tone.
Due to the fact that tuning one string influences the tuning of all other strings it might be advantageous according to an embodiment of the invention to have a tuning device with a display for each string and e.g. also displays for additional information. This embodiment would be very useful in the situation where it is important that all strings are exactly correctly tuned. Such exactly correct tuning could be obtained by having a display or display section for each string e.g. displaying the tune of the sting in a stroboscopic mode.
In addition to monophonic and polyphonic input signals, a third and fourth condition exist: If no input signal is present the tuning device should also have a well-defined behaviour, e.g. set the display appropriately, e.g. blank it. If on the other hand a signal is present but of a noisy character without distinct pitches, the tuning devices should also have a well-defined behaviour, e.g. by letting the display indicate that the input is invalid, e.g. by writing “error”, or blank the display.
A signal from a single string will primarily consist of a fundamental frequency and a sequence of partials with essentially integer multiples of the fundamental frequency. In the time domain this signal exhibits a repetitive pattern which in an autocorrelation analysis (or similar) also exhibits a simple repeated pattern. In the frequency domain, such a signal with a number of (almost) harmonic partials is also easily recognised.
A signal from two or more strings with no simple harmonic relationship is much more complex in nature than the signal from a single string.
A simple way to distinguish between a monophonic and a polyphonic input signal would be to sense the output level of the six bandpass filters, one for each string. This method is not suitable in all situations, however, e.g. if all strings but one are out of tune, as the outputs of one bandpass filter will be strong whereas the outputs of the remaining bandpass filters would be close to zero. Such a simple classification mechanism would falsely indicate a monophonic signal in this case.
Another simple way of classifying the input signal is to simply have the monophonic detector active all the time, and whenever it is able to establish a monophonic characteristic the input signal is classified as being monophonic, but if the monophonic detector is not able to distinguish a distinct monophonic characteristic the input signal is classified as being polyphonic, and the polyphonic pitch detector can be employed.
A better, and preferred, method to perform the classification between monophonic and polyphonic is to perform a correlation (or Fourier, or ASDF) analysis of the complete input signal and examining the resulting time of frequency domain pattern.
If a frequency spectrum is available, for example from a Fourier transform of the input signal, another simple method for determining the nature of the input signal can be used, in that the number of spectral peaks can be counted. The polyphonic signal for all six strings contains considerably more high spectral peaks than the spectrum for a single string.
The signal type classification means STCM may be implemented as a part of either the monophonic pitch detector MPD or the polyphonic pitch detector PPD.
Distinguishing between signals from a guitar and a bass guitar in polyphonic mode The standard tuning of guitar strings is, from low to high frequencies, E, A, D, G, B, E. Another very common musical instrument is the bass guitar (and the double bass) which due to the construction typically does not need tuning as often as a guitar, but tuning is of course needed.
The standard tuning of the four-string bass guitar (and double bass) is: E, A, D, G, which corresponds to the four lowest strings on a guitar, just tuned one octave lower. Some basses have five or six strings, however. A common tuning for a five-string bass is: B, E, A, D, G. The frequency range has thus been extended downwards by means of the B string below the E string. A common tuning for a six-string bass is: B, E, A, D, G, C. Compared to the five-string bass, the frequency range has been extended upwards by means of the C string above the G string. Compared to the tuning of a guitar this is a difference, as the guitar has a B string above the G string.
Due to these differences in the tones (chromas) in the nominal tunings of guitars and basses, the polyphonic tuner needs information on whether a guitar signal or a bass signal is input to the tuning device. A change of analysis frequencies should be made depending on this information. It is desirable if this change can occur automatically, based on the characteristics of the input signal.
A method to distinguish between guitar and bass signals is to measure the spectral characteristics of the input signal, and determine where the major part of the signal energy occurs at lower or higher frequencies. The so-called spectral centroid, known from the area of music information retrieval is a useful measurement of the spectral characteristics in this context. Other methods comprise comparing the outputs of the bandpass filters, or determining the lowest partial in the input signal.
A particularly advantageous embodiment of the invention therefore comprises means to change detection and display mode automatically depending on whether the input signal consist of the signal from a guitar or from a bass.
Final Remark
It is to be understood that details of the embodiments, hereunder different combinations of features, different sequences and different configuration parameters may differ from the described herein without deviating from the spirit of the invention.
This application claims the priority of U.S. Provisional Application Ser. No. 61/233,933 entitled “POLYPHONIC TUNER” filed on Aug. 14, 2009, the entire contents and substance of which are hereby incorporated in total by reference.
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