Patent Application
20060086238
1. Field of the Invention
The present invention relates to an apparatus and a method for reproducing a MIDI-based music file.
2. Description of the Related Art
To reproduce a MIDI (musical instrument digital interface) file into a real sound, many methods can be used. Representative methods include a frequency modulation (FM) synthesis method and a wave table synthesis method. The FM synthesis method reproduces a sound by synthesizing basic waveforms. Since the FM synthesis method does not require a separate sound source, it has an advantage of using a small amount of memory but has a disadvantage of not reproducing a natural sound close to an original sound. On the contrary, the wave table synthesis method stores sound sources for each instrument and each note of each instrument in advance and synthesizes these sound sources to reproduce a sound. The wave table synthesis method has a disadvantage of using a large amount of memory in storing the sound sources, but has an advantage of reproducing a natural sound close to an original sound.
To hear a sound in real-time through a MIDI file reproducing system, a process of synthesizing a sound using a MIDI file and a sound source should be performed in real-time. A process of synthesizing a sound requires a considerable amount of processor resources. Parts that use the processor resources in the MIDI file reproducer include an envelope generator. The envelope generator is used to generate the envelope of a sound waveform determining the size of the volume or the pitch of a sound. Therefore, the envelope generator has a considerable influence on sound quality and uses a large portion of the processor resources.
Here, the envelope includes an envelope for the volume and an envelope for the pitch. Referring to
When one note is reproduced by applying the envelope of
The MIDI file inputted to the MIDI parser 21 contains information regarding predetermined music stored in advance in a storage medium thereof. The MIDI file can include a plurality of notes and note reproduction times. A note is information representing a sound. For example, the note represents information (e.g., Do, Re, and Mi) regarding a musical scale. Since the note is not a real sound, it should be reproduced into actual sound sources. Also, the note reproduction time means a reproduction time of each of the notes contained in the MIDI file and is information regarding the same length of a sound. For example, when the reproduction time of a note “Re” is ⅛ second, a sound source that corresponds to the note “Re” is reproduced for ⅛ second when it is reproduced.
Sound sources for each instrument and each note of each instrument are registered in the wave table 24. A musical scale includes 1 to 128. There is a limitation in registering all of sound sources for the musical scale (i.e., notes contained therein) in the wave table 24. Therefore, sound source samples for only several representative notes are registered in the wave table 24.
When the reproduction time for the note is inputted, the frequency converter 23 judges whether a sound source for the relevant note is present in the wave table 24 and frequency-converts the note into a sound source that correspond to the relevant note. The frequency converter 23 may be an oscillator.
In the case where a sound source for the relevant note is not present in the wave table 24, the frequency converter 23 reads a predetermined sound source sample from the wave table 24 and frequency-converts the read sound source sample into a sound source sample that corresponds to the relevant note. In the case where a sound source for the relevant note is present in the wave table 24, the frequency converter 23 reads the relevant sound source sample from the wave table 24 and outputting the same without a separate frequency conversion. For example, in the case where a sound source sample registered in the wave table 24 is sampled by 20 kHz and a note of desired music is sampled by 40 kHz, the sound source sample is finally frequency-converted into 40 kHz and reproduced. That is, the sound source sample of 20 kHz can be frequency-converted and outputted into a sound source sample of 40 kHz by the frequency converter 23.
The above processes are repeatedly performed whenever the note reproduction time for each note is inputted. However, in the case where the frequency conversion is repeatedly performed whenever the note reproduction time for each note is inputted as described above, a considerable amount of operations is required, so that the relevant processor can be overloaded. Moreover, the relevant MIDI file should be reproduced and outputted in real-time. However, since the frequency conversion is performed for each note as described above, music may not be reproduced in real-time. In short, the MIDI reproducing apparatus can reproduce music substantially only in the case where it uses a considerable amount of processor resources.
Accordingly, the present invention is directed to an apparatus and a method for reproducing a MIDI file that substantially obviate one or more problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an apparatus and a method for reproducing a MIDI file, capable of reducing non-continuous points and noises thereof to allow the MIDI file to be reproduced in high quality by determining a time point that limits reproducing of the MIDI file and forcibly terminating the reproducing of the MIDI file at the determined reproduction limitation point when the MIDI file is reproduced.
Another object of the present invention is to provide an apparatus and a method for reproducing a MIDI file, capable of guaranteeing a high quality sound while using limited processor resources by determining a time point that limits reproducing of the MIDI file and finding out a zero crossing point to forcibly terminate the reproducing of the MIDI file at the zero crossing point when the MIDI file is reproduced.
A further another object of the present invention is to provide an apparatus and a method for reproducing a MIDI file, capable of guaranteeing a high quality sound while using limited processor resources by determining a time point that limits reproducing of the MIDI file and controlling a slope of an envelope to forcibly terminate the reproducing of the MIDI file at the determined reproduction limitation point when the MIDI file is reproduced.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, there is provided a method for reproducing a MIDI file including: extracting a plurality of notes and note reproduction times from the MIDI file; searching a point where envelope values of sound source samples after Note-Off are close to zero; determining the searched point as a point that limits a sound source sample value; and reflecting the determined limitation point to output the sound source samples according to the note reproduction times.
In the second aspect of the present invention, there is provided a method for reproducing a MIDI file including: extracting a plurality of notes and note reproduction times from the MIDI file; calculating envelope slopes of sound source samples after Note-Off; and applying the calculated envelope slopes to output the sound source samples according to the note reproduction times.
In the third aspect of the present invention, there is provided an apparatus for reproducing a MIDI file including: an element for extracting a plurality of notes and note reproduction times from the MIDI file; an element for finding out points where envelope values of sound source samples after Note-Off are close to zero; an element for determining the found points as points that limit the sound source samples; and an element for reflecting the determined limitation points to output the relevant sound samples according to the note reproduction times.
In the fourth aspect of the present invention, there is provided an apparatus for reproducing a MIDI file including: an element for extracting a plurality of notes and note reproduction times from the MIDI file; an element for calculating envelope slopes of sound source samples after Note-Off; and outputting the sound source samples according to the note reproduction times on the basis of the calculated envelope slopes
According to the present invention, it is possible to reduce a time consumed until the envelope value falls down to zero while minimizing noises heard to a human ear. Therefore, overload of a CPU is prevented, reproduction of high quality MIDI music can be performed by a CPU of low specification, and deterioration of sound quality can be prevented.
It is to be understood that both the foregoing general description and the following detailed description of the present invention are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle of the invention. In the drawings:
Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings.
When one note is reproduced by applying an envelope in a MIDI-based music file, the envelope after Note-Off should reduce and finally fall down to zero so as to reproduce the note in the most ideal manner. However, since it is difficult that a reproducing apparatus (e.g., a mobile terminal) having limited resources reproduces a note in this manner, the present invention includes an envelope analyzer and a Note-Off envelope processor, thereby making possible high quality reproduction of sound even when limited processor resources are used.
In an envelope for reproduction of a MIDI file, the envelope reduces as time elapses after Note-Off and the volume of a sound gradually diminishes and finally becomes zero. However, the envelope has a considerable size even while it approaches zero. When the envelop having this considerable size is limited without a particular consideration, non-continuous points are generated between a zero point and a point greater than the zero point, so that noises are heard to a human ear depending on cases.
The present invention minimizes generation of non-continuous points and noises by determining a point that limits the reproduction of a MIDI file as a point that can reduce damage of sound quality, and forcibly terminating the reproduction of the MIDI file at the determined reproduction limitation point when the MID file is reproduced.
Referring to
Here, as a method for finding out a point where a sample value is close to zero, a method for finding out a zero crossing point and determining that point as the point 120 that limits the sample value right before the zero crossing point, can be used.
The method for finding out the zero crossing point may be the following method, in which: a case where sample values before non-continuous points between a point greater than zero and a zero point are generated are less than zero, are found; a case where a sample value whose next sample value is greater than zero is found among the sample values that correspond to the above case; a sample value less than zero is determined as a point 120 that limits reproduction of the sample, and the sample is not reproduced after that point 120 and the sample value is fixed to zero. By doing so, a sample value that is closest to zero among the sample values in the vicinity of the limitation point 120 is changed into zero, so that a difference between the sample value at the limitation point 120 and zero is reduced and noises are reduced when a MIDI file is reproduced.
Referring to
When a MIDI file is inputted, the MIDI parser 121 parses the MIDI file to extract a plurality of notes and note reproduction times contained therein. Here, the note reproduction times mean respective reproduction times of the respective notes. The MIDI file can contain a plurality of notes and note reproduction times. A note is information representing a sound. For example, the note represents information (e.g., Do, Re, and Mi) regarding a musical scale. Since the note is not a real sound, it should be reproduced into actual sound sources. A musical scale can include a range of 1-128. A MIDI file can be a musical piece consisting of a start and an end of one song. This musical piece can include numerous musical scales and time lengths of respective musical scales. Therefore, a MIDI file can contain information regarding notes that correspond to respective musical scales and the reproduction times of the respective notes. The note reproduction time means a reproduction time of each of the notes contained in the MIDI file and is information regarding the same length of a sound. For example, when the reproduction time of a note “Re” is ⅛ second, a sound source that corresponds to the note “Re” is reproduced for ⅛ second when it is reproduced.
The plurality of notes extracted from the MIDI parser 121 are inputted to the MIDI sequencer 122. The MIDI file inputted to the MIDI parser 121 can contain tens of notes through 128 notes regarding a musical scale. Therefore, the notes contained in the MIDI file cannot be reproduced using sound source samples registered in the wave table 126. Instead, the sound source samples registered in the wave table 126 are frequency-converted into sound source samples that correspond to notes contained in the MIDI file and reproduced.
The MIDI sequencer 122 that receives the respective reproduction times of respective notes from the MIDI parser 121 sequentially reads, from the wave table 126, sound source samples that correspond to respective notes according to the respective reproduction times of the respective notes and outputting the same, so that the reproduction of the MIDI file can be performed. However, when a note contained in the MIDI file is reproduced, the volume of a sound sample after Note-Off should reduce to be close zero so as to reproduce the note in the most ideal manner. For that purpose, the envelope value of a sound source sample after Note-Off is searched to capture a point where the envelope value approaches zero and this point should be applied as a limitation point 120. Otherwise, a non-continuous point where the envelope value rapidly reduces to zero is generated to have an adverse influence on sound quality. For that purpose, the zero crossing point searching part 123 captures the zero crossing point of the envelope. The zero crossing point captured through the zero crossing point searching part 123 is applied to the envelope as the limitation point 120 by the envelope applying part 124. Therefore, a noise of a sound source generated from the envelope is eliminated and a high quality sound can be secured even in the case where a sound is synthesized using limited processor resources.
To solve this problem, the slope of the envelope is allowed to fall down without cutting for a predetermined period of time before the point where a non-continuous point between a point greater than zero and a zero point is generated, so that the envelope may reach a value close to zero at the point where the non-continuous point is generated. At this point, when a degree by which the slope falls down is uniformly applied to all the cases, sound quality may be distorted because the volume of a sound at the point at which the slope falls down and a time duration between the point at which the slope falls down and a limitation time are different depending on notes and a circumstance where notes are tied. Therefore, the present invention differently applies the degree by which the slope of the envelope falls down depending on these two factors.
First, as the volume of a sound at the point at which the slope falls down is large, the degree by which the slope falls down should be large. That is, the volume of the sound at the point at which the slope falls down is proportional to the degree by which slope falls down. Also, as the duration between the point at which the slope falls down and the limitation point is long, the degree by which slope falls down should be small. That is, the duration between the point at which the slope falls down and the limitation point is inversely proportional to the degree by which slope falls down. Above relationship is given by the following equation. Assuming that the volume of a sound at a point at which slope falls down is Vs, duration between the point at which the slope falls down and the limitation point is Td, and a degree by which the slope falls down is Yd,
Yd=C×Vs/Td,
where C is a proportional constant.
When the shape of the envelope illustrated in
Referring to
When a MIDI file is inputted, the MIDI parser 221 parses the MIDI file to extract a plurality of notes and note reproduction times contained therein. Here, the note reproduction times mean respective reproduction times of the respective notes. The extracted notes are inputted to the MIDI sequencer 222.
The present invention reduces the slope of Note-Off of a sound source sample to minimize a use amount of a processor and allow a MIDI file to be reproduced in high quality. The MIDI sequencer 222 that receives the respective reproduction times of respective notes from the MIDI parser 221 sequentially reads, from the wave table 227, sound source samples that correspond to respective notes according to the respective reproduction times of the respective notes and outputting the same, so that the reproduction of the MIDI file can be performed.
When notes contained in a MIDI file are reproduced, Release Time 114 after Note-Off 116 should be maintained so as to allow a most ideal sound to be reproduced for each note. For that purpose, the slope of the envelope should be changed and applied depending on circumstance after the Note-Off 116. Otherwise, the Release Time 114 is lengthened and sound quality can be distorted. In the present invention, the time limitation part 223 controls a time Td consumed until an envelope value becomes zero after the Note-Off 116. Also, the slope calculator 224 calculates the slope of an envelope using Td and the volume Vs of a sound at the Note-Off 116 of an envelope. The slope of the calculated envelope is proportional to Vs and inversely proportional to Td. The slope of the envelope calculated in this manner is applied to a sound source sample through the envelope applying part 225. That is, an envelope slope 118 is controlled on the basis of Yd=C×Vs/Td, so that the envelope reduces smoothly and stably without cutting and thus sound quality can improve.
It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2004-0084921 | Oct 2004 | KR | national |
| 10-2004-0084922 | Oct 2004 | KR | national |
