The present document is based on Japanese Priority Application JP2003-285294 filed in the Japanese Patent Office on Aug. 1, 2003, the content in which being incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a microphone apparatus and a noise reduction method which are suitable for use in recording apparatus having a built-in camera, for example.
2. Description of the Related Art
The applicant of this patent application has proposed in an earlier patent application, Japanese Application Publication No. 2002-367234, a microphone apparatus and a vibration-dependent noise reduction method and apparatus having a plurality of microphone units which are disposed in opposed relationship. This is a so-called sensorless noise reduction technique because a microphone to pick-up an audio signal is also used as a vibration sensor.
However, the microphone units to be used in such reduction technique must satisfy the following requirements. Firstly, non-directional microphone units having non directional characteristics must be used. Secondly, the microphone units must be disposed close to one another with their sound receiving faces thereof facing to one another. Thirdly, the use of a plurality of microphone units is essential.
In addition, Japanese Patent Application Publication No. H8-272377 discloses a noise reduction apparatus including a sensor for detecting a signal having strong correlation to a noise, an adaptive FIR filter for generating a cancellation signal which is opposite in phase to the noise and the same acoustic pressure as the noise based on the detected signal, an adder for combining the generated cancellation signal and the noise signal from the built-in microphone, and coefficient renewal means for sequentially calculating and renewing coefficients of the adaptive FIR filter in order to maximize the amount of reduction of the noise based on the residual signal resulting from the combination by the adder.
As a result, some problems arise in cases where requirements of the microphone units as described in Japanese patent application No. 2002-367234 are not satisfied, such as when a directional microphone unit like a unidirectional microphone or the like is used, in monaural microphone apparatus employing a single microphone unit, in apparatus of such construction as employing microphones disposed far apart with considerable distance therebetween, and the like.
On the contrary, as shown in
Although Japanese Patent Application Publication No. H8-272377 discloses a technique to detect by sensor a signal having high correlation to noise which is to be rejected, and to generate a cancellation signal for reducing the noise by an adaptive filter based on the detected signal, its noise reduction performance is poor. On the contrary, the present invention differs from it in that, in order to improve the noise reduction performance by further enhancing correlation between the signal of the sensor and the noise signal of the microphone, vibration detection directions of the microphone and the sensor, or the output polarities in addition thereto are made in agreement.
In addition, as shown in
As apparent from the foregoing, merits of extracting the reference signal 97 to be inputted to the adaptive filter 95 by the microphones 92 rather than the sensor 93 include that, since the noise signal 96 to be rejected and the reference signal 97 are obtained from the microphones 92 which are mounted on the same position, there is no delay time difference between the both signals and the correlation is relatively high. Accordingly, the pseudo noise signal 98 can be easily generated by the adaptive filter 95. On the contrary, in case of separating the microphones 92 and the sensor 93, experiments have been made by the applicants to prove that the difference in mounting location causes different transmission characteristics from a noise source 91, thereby making the adaptive filter 95 more complicate in construction because of the need for correcting the delay time difference and making it difficult to improve noise reduction performance because of possibly poor correlation between them.
The present invention has been conceived in consideration of the above circumstances and it proposes to realize vibration dependent noise reduction even in the above cases by providing a microphone to pick up an audio signal and further a vibration sensor.
Moreover, in recent years, a vibration sensor known as an impact sensor or a shock sensor is built in a disk device such as an HDD (Hard Disk Drive), a DVD (Digital Versatile Disk), a CD-R (write once) or the like for the purpose of enhancing the vibration resistance performance of such device. In a built-in camera type video recording/play-back (reproducing) apparatus including an HDD which is believed to be the mainstream product in future, the vibration sensor in the HDD is commonly used for easily detecting and reducing vibration noise, which is generated from such device, without providing an additional sensor.
A microphone apparatus according to a preferred embodiment of the present invention includes one or more microphones, one or more sensors, a noise extraction means for extracting a noise bandwidth section in an output signal from the sensor, an adaptive filter for each microphone which receives the output signal of the noise extraction means as a reference input signal, and a operation means for subtracting the output signal of the adaptive filter from the output signal of the respective microphone, wherein directions of vibration detection of the microphone and the sensor match, or, in addition, output polarities of the vibration signals of the microphone and the sensor match.
According to the preferred embodiment of the present invention, since there is no restriction of disposing at least two or more non-directional microphone units close to each other and in an opposed relationship, the noise reduction circuit according to the preferred embodiment of the present invention is capable of canceling vibration dependent noise from the audio signal of the microphone even in devices such as, for example, those employing a single microphone, a directional microphone having a unidirectional characteristic or the like, or in apparatus having a construction where opposed disposition is impossible.
Also, a microphone apparatus according to another preferred embodiment of the present invention includes a plurality of microphones, one or more sensor, a first operation means for outputting a difference component between the output signals from the plurality of microphones, a noise extraction means for extracting a noise bandwidth section in the output signal of the first operation means, an adaptive filter for each microphone for receiving the output signal of the noise extraction means as a reference signal, and a second operation means for subtracting the output signal of the adaptive filter from the output signal of the respective microphone, wherein directions of vibration detection of the microphone and the sensor match, or, in addition, output polarities of the vibration signals of the microphone and the sensor match and noise reduction is inhibited by not carrying out the subtraction by the second operation means if the signal level of the sensor is equal to or lower than a designated level.
According to the preferred embodiment of the present invention, the use of a vibration sensor together with a plurality of microphone units makes it possible to accurately pick up and use only the target vibration noise, thereby enabling to cancel out the vibration dependent noise from the audio signal of the microphone without the need for disposing the microphone unit in an opposed relationship.
Moreover, the noise reduction method according to another preferred embodiment of the present invention employs a microphone apparatus having one or more microphones, one ore more sensors, a noise extraction means for extracting a noise bandwidth section from the output signal of the sensor, an adaptive filter for each microphone to receive the output signal of the sensor as a reference input signal, and an operation means for subtracting the output signal of the adaptive filter from the output signal of each microphone, wherein directions of vibration detection of the microphone and the sensor match, or, in addition, output polarities of the vibration signals of the microphone and the sensor match, the method including the steps of extracting a noise bandwidth section from the output signal of the sensor by the noise extraction means, further outputting a pseudo noise signal corresponding to the respective microphone by inputting the output signal of the noise extraction means by the adaptive filter, and subtracting the output signal of the adaptive filter from the output signal of the respective microphone by the operation means.
According to another preferred embodiment of the present invention, it is possible to cancel vibration dependent noise in the audio signal from a microphone by the noise reduction processing of the present invention even in cases such as, for example, when only a single microphone is used, a directional microphone having a unidirectional characteristic or the like is used, or when an apparatus has a construction in which disposition in an opposed relationship is impossible, because there is no restriction of disposing at least two or more microphones close together and in opposed relationship like in the earlier patent application.
Also, the noise reduction method according to a preferred embodiment of the present invention is used in a microphone apparatus having a plurality of microphones, one or more sensor, first operation means for outputting a difference component between output signals of a plurality of microphones, noise extraction means for extracting a noise bandwidth section from the output signal of the first operation means, an adaptive filter corresponding to the respective microphone by receiving the output signal of the noise extraction means as the reference input signal and second operation means for subtracting the output signal of the adaptive filter from the respective microphone, wherein directions of vibration detection of the microphone and the sensor match, or, in addition, output polarities of the vibration signals of the microphone and the sensor match, and the method comprises the steps of outputting a difference component between the output signals of a plurality of microphones by the first operation means, extracting a noise bandwidth section in the output signal of the first operation means, outputting a pseudo noise signal corresponding to the respective microphones with the output signal of the noise extraction means as the reference input signal by the adaptive filter, subtracting the output signal of the adaptive filter from the output signal of the respective microphone by the second operation means, and prohibiting the subtraction by the second operation means when the signal level of the sensor is equal to or less than a designated level.
According to a preferred embodiment of the present invention, by using a plurality of microphone units together with the vibration sensor, the vibration dependent noise can be cancelled out from the audio signal of the microphone without disposing microphone units in an opposed relationship like the case in the earlier patent application, because noise reduction processing can be performed by accurately picking up only the target vibration noise.
Also, the recording apparatus according to a preferred embodiment of the present invention uses a microphone apparatus having one or more microphones, one or more a noise extraction means for extracting a noise bandwidth section from the output signal of the sensor, an adaptive filter for each microphone for receiving the output signal of the noise extraction means as the reference input signal, and an operation means for subtracting the output signal of the adaptive filter from the output signal of the respective microphone, thereby recording the output signal of the microphone on a recording medium by recording means which is driven by driving means, wherein directions of vibration detection of the microphone and the sensor match, or, in addition, output polarities of the vibration signals of the microphone and the sensor match.
According to a preferred embodiment of the present invention, the microphone apparatus which performs noise reduction according to a preferred embodiment of the present invention is capable of canceling only the vibration dependent noise from the audio signal of the microphone even in the recording apparatus such as, for example, those using a single microphone, using a directional microphone having unidirectional characteristic or the like, or having the construction in which opposed disposition is impossible, because there is no restriction of disposing at least two or more non-directional microphone units close to one another and in an opposed relationship like in the earlier patent application.
Also, the recording apparatus according to a preferred embodiment of the present invention is for recording the output signal of a microphone apparatus having a plurality of microphones, one or more sensors, a first operation means for outputting difference components between output signals of the plurality of microphones, noise extraction means for extracting the noise bandwidth section in the output signal of the first operation means, an adaptive filter for each microphone for receiving the output signal of the respective microphone as the reference input signal, and a second operation means for subtracting the output signal of the adaptive filter from the output signal of the respective microphone, wherein directions of vibration detection of the microphone and the sensor match, or, in addition, output polarities of the vibration signals of the microphone and the sensor match, and noise reduction is prohibited by not performing the subtraction of the second operation means when the signal level of the sensor is equal to or lower than a designated level.
According to a preferred embodiment of the present invention, by using a plurality of microphone units together with the vibration sensor, it is possible to accurately pick up and use only the target vibration noise, thereby canceling out the vibration dependent noise from the audio signal of the microphone and recording only the audio signal even in the recording apparatus having a construction in which microphone units cannot be disposed in an opposed relationship like in the earlier patent application.
For example, by commonly using the vibration sensor, the impact sensor or the shock sensor which is built in a disk device such as an HDD, a DVD, a CD, a CD-R or the like for the purpose of improving vibration resistant performance, the recording apparatus according to a preferred embodiment of the present invention is capable of detecting and reducing vibration noise which is generated in such apparatus without providing a new or additional sensor.
Therefore, the microphone apparatus according to the preferred embodiments of the present invention proposes a noise reduction technique which uses a sensor for converting vibration into electrical signal, thereby reducing vibration dependent noise by using the sensor together with the microphone. Since there is no restriction in locations of the microphone unit and the sensor, the microphone apparatus according to the preferred embodiment of the present invention can be used in a wide range of electrical machines and appliances. Moreover, by making the vibration detection directions of the microphone and the sensor or the output polarities in addition thereto in agreement and by improving the converging characteristic of the adaptive filter, reduction effect can be achieved even with small number of taps.
Furthermore, since subtraction by the second operation means is interrupted when the signal level from the sensor is equal to or less than a designated level, it is possible to accurately pick up and reduce only the target vibration noise.
On the other hand, the noise reduction method according to the preferred embodiment of the present invention is capable of reducing noise of a wide range of electrical machines and appliances to which the microphone apparatus according to the preferred embodiment of the present invention is applied, by using the sensor together with the microphone for reducing vibration dependent noise, because there is no restriction to the location of the microphone unit and the sensor. Again, by making directions of vibration detection of the microphone and the sensor match, or, in addition, output polarities of the vibration signals of the microphone and the sensor match, it is possible to improve the correlation between them and improve converging characteristics of the adaptive filter, thereby achieving reduction effect by filter processing with small number of taps.
In addition, by interrupting the subtraction by the second operation means when the signal level from the sensor is equal to or less than a designated level, it is possible to accurately pick up only targeted vibration noise by the sensor and reduce such noise.
The recording apparatus according to the preferred embodiments of the present invention still proposes a noise reduction technique using the sensor for converting vibration into electrical signal and thus reducing vibration dependent noise by using the sensor together with the microphone. Since there is no restriction to location of the microphone unit and the sensor, it is possible to use the microphone for reducing noise of a wider range of recording apparatus than prior arts, thereby enabling to cancel out noise and record only the audio signal. Again, by making the vibration detection directions of the microphone and the sensor or the output polarities in addition thereto in agreement, it is possible to improve the correlation and improve the converging characteristic of the adaptive filter, thereby achieving reduction effect with small number of taps.
Moreover, by interrupting the subtraction by the second operation means when the signal level of the sensor is equal to or less than a designated level, it is possible to accurately pick up by the sensor and reduce only the target vibration noise, thereby canceling out the noise and recording only the audio signal.
The above and other objects and features of the preferred embodiments of the present invention will become more apparent to those of ordinary skill in the art from the following detailed description taken in conjunction with the accompanying drawings in which:
In a video camera such as a home use digital video camera and the like, it is most likely to pick up sound by a built-in microphone apparatus. Since downsizing of electrical machines and appliances is accelerated in recent years, a recording apparatus such as a VTR, a disk device or the like and a microphone which is built in such machines and appliances are disposed at closer locations between them, thereby causing a problem that vibration noise and acoustic noise generated by such recording apparatus invade easily into the microphone. Similarly, downsizing may cause a problem that the user unintentionally touches the built-in microphone or surroundings when one is operating various camera features such as zooming or focusing as well as operating switches when taking pictures, thereby introducing undesirable noise through the cabinet and causing uncomfortable touching noise at time of play-back.
Incidentally, in a case of taking pictures (capturing images) in relatively quiet environment, since an internal AGC (Automatic Gain Control) circuit increases the microphone sensitivity, even slight touch noise may be very harsh to the ears. Furthermore, since it is general in a video camera that a non-directional microphone unit is used so that an operation circuit changes it to have a directional characteristic, there are possibilities to cause a problem that the noise frequency bandwidth is enhanced by proximity effect peculiar to directional characteristic, so it is emphasized rather than the intended audio signal.
In order to reduce such noise, it is conventional to float the microphone unit of the built-in microphone from the cabinet by using an insulator such as a rubber dumper or the like or to employ such construction of hanging the microphone unit in air by using a rubber wire or the like, thereby absorbing the vibration which is conducted from the cabinet or preventing conduction of such noise. Unfortunately, such conventional techniques are not enough to completely suppress vibration because such insulator exhibits no effect to strong vibration or vibration of a certain frequency and conversely, there are cases to cause resonance in peculiar frequencies. Accordingly, it makes the mechanical design very difficult and is an obstacle to cost reduction and downsizing.
Furthermore, noise caused by the above mentioned touch noise is not only vibration which is conducted through the cabinet but also acoustic noise conducted simultaneously with the vibration through air, thereby making noise transmission paths to the microphone unit very complicated. Therefore, there is a limitation in noise reduction by the conventional passive methods and thus it is difficult to achieve the level which satisfies the user.
Therefore, the present invention aims at solving the above-mentioned problems without the need for structural measures to isolate the microphone unit but rather positively picking up vibration noise and canceling out the generated vibration noise by means of circuitry. In addition, the picked up vibration noise is supplied to an adaptive filter as the reference input signal for canceling out the acoustic noise which is generated at the same timing.
In the above-mentioned manner, the present invention performs noise reduction processing targeted to all kinds of noise which are generated depending on vibration.
Now, features of the present invention will be described hereunder by reference to
Like the case in the earlier Japanese Patent Application Publication No. 2002-367234 (Noise Reduction Apparatus and Method), the present invention does not require a plurality of microphones for inputting an audio signal and may use a single microphone. Moreover, it is possible to use not only a non-directional microphone but also a directional microphone such as a unidirectional microphone, a bidirectional microphone or the like.
In addition, in
Now, the example of preferred embodiment of the microphone apparatus in
Then, the audio signal of the AMP 3 is supplied to a delay unit 5 for causing a delay equivalent to the processing time of the noise extraction means 6 and the adaptive filter 7 before being inputted to the plus (+) side terminal of an adder 8 in phase with the pseudo noise signal Y which is inputted to the minus (−) side terminal for outputting from the output terminal 9. Furthermore, the output signal is fed back to the adaptive filter 7 as an error signal E. By operating the adaptive filter 7 so that the error signal will be always the minimum, it is possible to obtain the audio signal reduced the vibration component from the terminal 9.
Then, the relationship between the microphone diaphragm and the sensor will be described in
The present invention features in that the vibration detection sensitivity directions 13, 15 of the microphone 1 and the sensor 2, which are used therein, are matched with each other to enhance the correlation between the two output signals, thereby reducing efficiently the vibration component in the subsequent stage adaptive processing.
In
It is to be noted in the example of preferred embodiment of present invention that the microphone and the sensor are not necessarily required to dispose close to each other. For instance, in an example as shown in
At this event, when the generated mechanical vibration and the acoustic vibration noise are inputted to the microphone, it is also possible to reduce such vibration component by the use of the embodiment 1 of the microphone apparatus in
Now, a construction and an operation of the sensor will be described hereunder.
Firstly,
According to
Accordingly, as shown in
At this event, the waveform correlation can be further improved by equalizing the polarities and delay times of the noise waveform generated in the audio microphone as shown in
Now, the adaptive filter 7 as shown in
Firstly, a signal which has high correlation with the target noise to be rejected is inputted as the reference input X in
(Mathematical Expression 1)
Furthermore, the LMS operation processing unit 35 performs operations of the respective adaptive filter coefficients Wo through Wm in accordance with the following Mathematical Expression 2 based on the reference input X and the error signal E for renewing them.
Wk=Wk−1+2μ·Ek−1·Xk−1 (Mathematical Expression 2)
In Mathematical Expression 2, each small letter k represents sampling time passage. Assuming that Wk for the k-th sampling is the adaptive filter coefficient at present, Wk−1 represents the adaptive filter coefficient for the (k−1)-th sampling, i.e., the adaptive filter coefficient for the past sampling by 1. On the other hand, μ is known as the step gain or the step size, which is a parameter to determine the converging speed in the LMS algorithm. Since a larger μ value means faster converging speed but poorer in accuracy after conversion, while a smaller μ value means slower converging speed but increases accuracy after conversion. Optimum value is set depending on the conditions of the adaptive system to be used. On the other hand, the inputted error signal E will be described hereinafter.
Now, the LMS operation processing unit 35 renews the aforementioned adaptive filter coefficient W in accordance with Mathematical Expression 2 so that the signal having high correlation to the reference input X included in the error signal E will be always minimized.
Then, description will be made on
Firstly, microphones 41, 42 are respectively right channel (Rch) and left channel (Lch) microphone units used for audio input similarly to the microphone 1 in
Now, a description will be made hereunder on a third example of the microphone apparatus according to a preferred embodiment of the present invention, as shown in
The difference component (differential component) of the output signals of the microphone 61 and the microphone 62, which is outputted from the aforementioned adder 69, contains a large portion of difference signals between the audio signals due to different mounting locations of the respective microphones and also the vibration signal. This is caused due to difference in spatial distance from the sound source for the audio signals, while due to difference in transfer function from the vibration source for the vibration signal. Incidentally, in case of a video recording apparatus with a built-in camera, it is most likely that the sound source is located sufficiently long distance as compared to the distance of mounting the microphones. On the other hand, since vibration source in the video recording apparatus with a built-in camera is within the main body of the recording apparatus, such vibration propagates from the distance substantially equal to the distance between the mounted microphones. Accordingly, the sound signals which are inputted to the microphone 61 and the microphone 62 are relatively equal distance with respect to the sound source, thereby having a high correlation. Since the vibration signal has a lower correlation than the audio signal, subtraction of these signals by the aforementioned adder 69 may result in producing more vibration signal than the audio signal.
Moreover, if the aforementioned comparator 67 is configured, for example, to output an ON signal when the vibration signal outputted from the sensor 63 is larger than the level set by the REF input 68, while outputting an OFF signal when it is smaller, the ON/OFF binary signal is inputted to the noise extraction means 70. By configuring the noise extraction means 70 to extract noise and output the vibration signal component when it is ON, while outputting a zero signal when it is OFF, it is possible to extract only the vibration signal which is then inputted to the adaptive filters 73, 74. A detailed description will be omitted because it operates similar to
It is to be noted in the example of preferred embodiment of the apparatus as shown in
Although one sensor is used in the embodiments mentioned as shown in
Now, description will be made hereunder on a fourth example of the microphone apparatus according to another preferred embodiment of the present invention as shown in
Firstly,
It is to be noted that the reference signal to be inputted to the adaptive filters 73, 74 in
Furthermore, description will be made on a fifth example of the microphone apparatus according to another preferred embodiment of the present invention as shown in
Generally, these motors have various built-in sensors for rotation and phase servo purposes, thereby reading out such information as the current rotation speed and phase. Such information is supplied to the various drive units 81 depending on the purposes of optimizing the drive. Therefore, since the ON/OFF signal is obtained from the various drive devices 81 in synchronism with the drive signal for the motors 84, 85 which are noise sources, it is similarly possible to turn on or off the noise reduction function by applying such signal to control terminals of the switches SW 82, 83. Although the switches SW 82, 83 for disconnecting or opening the outputs are connected to the adaptive filters 73, 74 in
The present invention can be applied to noise reduction processing of a driving motor in a disk device such as an HDD device, a DVD, a CD, a CD-R or the like which is installed in, for example, a recording apparatus with a built-in camera.
Furthermore, it should be understood by those of ordinary skill in the art that the descriptions above show mere examples of preferred embodiments of the present invention. Therefore, the present invention should not limited to such embodiments, so that many other modifications, variations, combinations, sub-combinations, etc. of such embodiments and equivalents thereof may be made without departing from the scope and spirit of the present invention.
Number | Date | Country | Kind |
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2003-285294 | Aug 2003 | JP | national |