JP2009296297A - Sound signal processing device and method - Google Patents

Abstract

By controlling and outputting the frequency characteristics of a sound source signal in accordance with the level of ambient noise, especially when the ambient noise level is reduced, sound to the surroundings is maintained while maintaining ease of listening to the sound. Reduce leakage.
An ambient audio signal detection unit (102) captures an ambient audio signal which is a mixed signal of an output audio signal emitted from an audio output unit (109) and a noise signal emitted from an ambient noise generation source, and an ambient noise signal detection unit (103). The ambient noise signal of the silent part is taken out by the background noise signal, the background noise signal of the ambient noise level in the section where the ambient noise level is small is taken out by the background noise level detection means 105, and input by the frequency characteristic control means 107 as the background noise level decreases. The low frequency range of the audio signal is attenuated and output as an output audio signal.
[Selection] Figure 1

Description

  The present invention is an apparatus for reproducing an input audio signal (sound source signal) using means such as a speaker, and is provided with a means for measuring an ambient noise level, adapted to the measured ambient noise level and input. The present invention relates to an apparatus for optimally adjusting acoustic characteristics including frequency characteristics and volume level of a reproduced audio signal by performing signal processing on the audio signal.

  Due to a property called masking phenomenon, human hearing can be heard even at low volume when the ambient noise level is low, but low volume sound can be heard as the ambient noise level increases. It becomes impossible. That is, on the basis of ease of listening, it is necessary to reproduce sound at a higher volume in an environment where the ambient noise level is high. As a device that controls the playback volume (output audio level) based on such auditory characteristics, the ambient noise signal is obtained by using a microphone, etc., and the ambient noise level is calculated and output in accordance with the calculated ambient noise level. There is a device for adjusting the sound level.

  In such a device, it is most important to correctly calculate the ambient noise level, but in general, the ambient noise signal obtained using a microphone or the like is the sound generated by the device itself in addition to the original ambient noise signal. Includes signals and so on. Therefore, it is necessary to remove the sound signal generated by the device itself from the acquired ambient noise signal and extract only the original ambient noise signal.

For this purpose, for example, in the apparatus disclosed by Patent Document 1, based on the level of the acquired ambient noise signal, means for determining whether or not the acquired ambient noise signal is only the original ambient noise signal. Is provided. As a result, only the original ambient noise signal is separated, and the level and frequency characteristics of the output signal are adjusted according to the signal level and frequency characteristics, thereby improving the ease of listening to the sound.
Japanese Patent Laid-Open No. 08-265075

  However, in the prior art, by optimizing the volume and sound quality of the reproduced sound, it is possible to perform control with less discomfort for ease of listening especially when the ambient noise level is high and changes in the ambient noise level. It was aimed. Therefore, it is possible to adapt to changes in ambient noise level over a relatively short time, but adaptation to changes in ambient noise level over a long time is particularly strongly affected by local ambient noise level increases. It was unsuitable. Further, in the prior art, the sound volume and sound quality are optimized for the purpose of improving the listener's ease of listening, which is not suitable for the purpose of preventing sound leakage to the surrounding environment.

  In order to solve the above-described problems, an audio signal processing device according to the present invention includes an ambient audio signal detection unit that detects an ambient audio signal in an acoustic space, a silence part detection unit that detects a silence part of an input audio signal, and the silence unit. Ambient noise signal detecting means for detecting an ambient noise signal that is the ambient audio signal in Ambient noise, an ambient noise level change detecting means for detecting a level change of the ambient noise signal, and the level change of the ambient noise signal is small A background noise level detecting means for detecting a background noise level which is a level of an ambient noise signal; and a sound output signal for controlling characteristics of the input sound signal based on the background noise level and outputting the sound to the acoustic space. Output characteristic control means.

  The audio signal processing device of the present invention includes an ambient audio level detection unit that detects an ambient audio level that is a level of an ambient audio signal in an acoustic space, a silence part detection unit that detects a silence part of an input audio signal, Ambient noise level detecting means for detecting an ambient noise level that is the ambient voice level in the silent part, an ambient noise level change detecting means for detecting a change in the ambient noise level, and the change when the change in the ambient noise level is small A background noise level detecting means for detecting a background noise level which is an ambient noise level, and a characteristic of the input audio signal is controlled based on the background noise level, and an audio output signal for outputting to the acoustic space is output. Characteristic control means.

  Further, the characteristic control means controls to attenuate a low frequency range of the input audio signal as the background noise level decreases.

  In addition, the characteristic control means performs control so as to further attenuate the high frequency range of the input audio signal as the background noise level decreases.

  The characteristic control means controls the volume of the input audio signal to decrease as the background noise level decreases.

  In addition, the characteristic control means controls to lower the volume of the input audio signal and attenuate the low frequency range of the sound source signal as the background noise level decreases.

  Further, the characteristic control means lowers the volume of the input audio signal as the background noise level decreases in a predetermined range, and further attenuates a low frequency range of the sound source signal in a range smaller than the predetermined range. It is characterized by controlling to.

  Further, the characteristic control means controls the volume of the input audio signal so as to change by the change of the background noise level.

  The characteristic control means controls the volume of the input audio signal to change less than the change in the background noise level.

  The sound signal processing device of the present invention adapts to the ambient noise level and optimally controls the sound quality and volume of the output sound, thereby maintaining the ease of listening to the sound while the ambient noise level is low. Leakage of output sound to the surrounding environment can be reduced.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

(Embodiment 1)
The configuration of Embodiment 1 of the present invention is shown in FIG. The input audio signal is input to the silent part detecting means 101. Any known method may be used as the detection method used by the silent part detecting means 101. For example, the input audio signal is divided into frames for each predetermined time, and the average energy of the audio signal of each frame is calculated. A method of determining the absolute value and the degree of change between adjacent frames by comparing with a predetermined threshold can be used.

  The ambient audio signal detection means 102 is, for example, a microphone device, and is built in the audio signal processing device of the present invention, or installed separately from the audio signal processing device of the present invention as an external microphone.

  Based on the detection result of the silent part detecting unit 101, the ambient noise signal detecting unit 103 detects the ambient audio signal detected by the ambient audio signal detecting unit 102 from the acoustic space only in the time interval in which the silent part of the input audio signal is detected. Captured and detected as ambient noise signal. The ambient noise level change detecting means 104 detects the level change of the input ambient noise signal and outputs it as the ambient noise level change. Details of the operation of the ambient noise level change detecting means 104 will be described later.

  The background noise level detection means 105 takes in the ambient noise signal and outputs it as a background noise level only in a time interval in which it is determined that the level change of the ambient noise signal is small based on the ambient noise level change. The frequency characteristic parameter calculating means 106 calculates a frequency characteristic parameter based on the background noise level. Details of operations of the background noise level detection means 105 and the frequency characteristic parameter calculation means 106 will be described later. The frequency characteristic control means 107 controls the frequency characteristic of the input audio signal according to the frequency characteristic parameter. The output audio signal of the characteristic control unit 108 including the frequency characteristic control unit 107 is output to the acoustic space by the audio output unit 109. The audio output means 109 is, for example, a speaker device.

  In the audio signal processing apparatus shown in FIG. 1, the ambient audio signal itself is detected by the ambient audio signal detection unit 102, the ambient audio signal itself is captured by the ambient noise signal detection unit 103, and the background noise level detection unit 105. The ambient noise signal itself is captured by the ambient sound signal, but instead, the ambient audio signal detection means 102 acquires the ambient audio signal level in the acoustic space, and the ambient noise signal detection means 103 captures the ambient audio signal level. It is equivalent even if the background noise level detecting means 105 captures the level of the ambient noise signal.

  The level of each signal is not limited to the amplitude of the signal, but may be the energy of the signal.

  Next, the operation of the ambient noise level change detecting means 104 will be described. The ambient audio signal detected by the ambient audio signal detection unit 102 is a mixed signal of the output audio signal emitted from the audio output unit 109 and the noise signal emitted from the ambient noise generation source. The state of the ambient audio signal detected can be roughly classified into four.

(1) Stationary ambient noise signal (2) Non-stationary ambient noise signal (3) Mixed signal of stationary ambient noise signal and output speech signal (4) Transient ambient noise signal and output speech signal Mixed signal Among these, the sections corresponding to (3) and (4) are deleted by the operation of the ambient noise signal detecting means 103. The sections corresponding to the remaining (1) and (2) are greatly different in nature particularly in terms of temporal level changes. This is because the steady ambient noise signal of (1) is generated as a result of mixing and averaging, for example, continuous operation sounds of various devices and various noise signals generated in the distance. The non-stationary ambient noise signal in (2) was generated by some action or phenomenon in the vicinity (passing a car, movement of a person, contact with an object, etc.) This is due to the difference in signal.

  FIG. 2 is a diagram for explaining the operation of the ambient noise level change detecting means 104. The input ambient noise signal is divided into frames of a predetermined time length. The energy of the ambient noise signal of the divided frame is calculated and held in the buffer. The buffer holds energy values for the past n frames. When the energy value of the current frame is input, the buffer discards the energy value of the oldest frame and updates it with the energy value of the current frame. For n energy values stored in the buffer, e (1) and e (2) are set in order from the energy value of the oldest frame, and the energy value of the newest frame (current frame) is e (n).

  Whether the ambient noise signal included in the current frame is non-stationary is determined by changing the energy value e (n) of the current frame to the energy value e (k) of the past frame (k is 1 to n−1). This can be determined by comparison. As an example of the comparison method, the ratio of the energy value e (n) of the current frame to the energy value e (n−1) of the previous frame is calculated to be the first energy ratio. Furthermore, an average value of energy values from e (1) to e (n-1) is calculated, and a ratio of e (n) to the calculated average value is calculated to obtain a second energy ratio. The first energy ratio represents a change in signal energy in a short time, and the second energy ratio is an index representing a change in signal energy in a longer time as compared with the first energy ratio.

  In this way, by using an index of energy change at different time lengths, more appropriate determination can be made in response to changes in various external noise signals. Each of the first and second energy ratios is compared with a predetermined threshold value to determine whether it is a steady section or an unsteady section. Table 1 shows the determination conditions. Here, the threshold values A, B, C, and D are predetermined values.

  Next, details of operations of the background noise level detection unit 105 and the frequency characteristic parameter calculation unit 106 will be described. FIG. 3 is a diagram showing a detailed configuration of the background noise level detection means 105 and the frequency characteristic parameter calculation means 106. First, in the background noise level detection means 105, the switch means 301 captures an ambient noise signal in a steady section where the ambient noise level change is small, that is, a background noise signal. This background noise signal is usually an intermittent signal. Only in the time interval in which the background noise signal is supplied, the energy calculation means 302 calculates the energy value of the background noise signal. The energy value smoothing means 303 switches the operation depending on whether or not the energy value of the background noise signal is input. When the energy value of the background noise signal is input, the value of the energy value buffer means 304 is updated according to the following equation.

However,
E _b (n): Energy value buffer value after update E _b (n-1): Energy value buffer value before update
e (n): Energy value of the input background noise signal α: Predetermined constant When the energy value of the background noise signal is not input, the value of the energy value buffer is held. The value of the energy value buffer calculated in this way is converted into a background noise level by conversion using a ratio with respect to a predetermined reference value. Subsequently, a frequency characteristic parameter is calculated based on the background noise level.

  Next, the operation of the frequency characteristic parameter calculation unit 106 will be described.

  The frequency characteristic parameter includes a low-frequency attenuation parameter and a high-frequency attenuation parameter. Generally, a low frequency signal (for example, about 300 Hz or less) included in an output audio signal has a characteristic that it is difficult to attenuate as compared with a signal in a frequency band higher than that, and the ambient environment such as at night when the background noise level decreases. Many of the sound leakage problems are mainly due to low-frequency signals.

  Accordingly, when it is detected that the value of the energy value buffer is decreased and the background noise level is decreased, a process of attenuating the low frequency range of the output audio signal is performed. In the low-frequency attenuation parameter calculation means 305, the value of the low-frequency attenuation parameter that determines the attenuation amount of the low frequency is given as a function corresponding to the background noise level.

  In the high-frequency attenuation parameter calculating means 306, the high-frequency attenuation parameter is associated with the low-frequency attenuation parameter, and the attenuation amount of the high-frequency signal (for example, about 7 kHz or more) is determined in accordance with the attenuation amount of the low-frequency signal. . This is because, when only the low frequency signal is attenuated in the audio signal, the high frequency signal is relatively emphasized and the sound quality is changed to be hard to hear.

  FIG. 4 shows an example of frequency characteristics realized by the low-frequency attenuation parameter and the high-frequency attenuation parameter. Curve A is the frequency characteristic of the output signal when the background noise level is a predetermined reference value (0 dB), and is a flat characteristic in the entire band. On the other hand, curve B is a case where the background noise level is 6 dB lower than the reference value, and the low and high frequencies are attenuated. Curve C is a case where the background noise level is 12 dB lower than the reference value, and the attenuation amount in the low and high ranges is larger than that in curve B.

  With the above configuration, when the background noise level decreases, the sound leakage to the surrounding environment can be reduced by adjusting the frequency characteristics of the output audio signal according to the degree of decrease in the background noise level.

  In the above description, the energy of the entire band of the background noise signal is used as the background noise level evaluation index, but other evaluation indices may be used. For example, after dividing the background noise signal into a plurality of frequency bands, the energy of each band is calculated, and the value obtained by weighting the calculated energy value of each band and then adding it can be used as an evaluation index. . By performing the weighting based on the auditory sensitivity for each frequency band, a more audibly preferable adjustment can be performed.

(Embodiment 2)
FIG. 5 shows the configuration of an audio signal processing apparatus according to Embodiment 2 of the present invention.

  The configuration of the second embodiment shown in FIG. 5 is provided with an audio level parameter calculation means 501 and an audio level control means 502 in addition to the configuration of the first embodiment shown in FIG. An audio level parameter is calculated based on the background noise level captured by the noise level detection unit 105, and an audio level control unit 502 controls the audio level of the audio signal whose frequency characteristics are controlled according to the calculated audio level parameter. By doing so, an output audio signal is generated. In this configuration, the components other than the audio level parameter calculating unit 501 and the audio level control unit 502 are the same as those in the first embodiment, and therefore, the same reference numerals are given in the drawing and the description thereof is omitted.

  The sound level parameter calculation unit 501 calculates a sound level parameter based on the background noise level detected by the background noise level detection unit 105. An example of the relationship between the background noise level and the voice level parameter is shown in FIG. In FIG. 6, the audio level parameter is defined as a change amount LP from the output audio level (volume volume value) set by the listener.

  Generally, when the use of an audio playback device is started or when the listener feels dissatisfied with the listening volume, the listener operates the volume volume to set it to an optimum volume. The output audio level at this time is a value indicated by S1. If the listener does not perform the volume control, it can be determined that the preset volume is the optimum value. When the background noise level N1 at the time when the volume is set to an optimum value is calculated and the difference from the output sound level S1 corresponding to the set volume volume is calculated, the background noise level required by the listener is obtained. And an output audio level RD (hereinafter referred to as a reference level difference) can be obtained.

  The reference level difference RD may be constant as long as the volume from the time of setting does not change significantly (for example, about + -6 dB). The sound level parameter calculating means refers to the calculated background noise level and calculates the sound level parameter so that the difference between the output sound level and the background noise level is equal to the reference level difference. For example, when the background noise level decreases by a width indicated by ND and becomes a value indicated by N2, the audio output level that maintains the reference level difference RD with respect to the background noise level N2 is S2. As a result, the sound level parameter is obtained as a difference LP between S1 and S2. The sound level control means controls and outputs the output sound level according to the sound level parameter.

  In calculating the audio level parameter, the range of the value taken by the audio level parameter may be limited so that the output audio level changes within a volume range in which the reference level difference can be regarded as constant.

  With the above configuration, while maintaining the difference between the background noise level required by the listener and the output sound level, the output sound level is controlled in accordance with the background noise level, thereby maintaining the ease of listening to the sound. However, sound leakage to the surrounding environment when the background noise level is reduced can be reduced.

  The reference level difference may be used after being corrected according to the background noise level. FIG. 7 shows that the reference level difference between the output sound level S3 and the background noise level N3 when the listener sets the volume is RD1, and the output sound level S4 and the background noise level N4 after the background noise level decreases. A reference level difference between them is assumed to be RD2, and RD2 is corrected so as to be larger than RD1. In this example, as a result of RD2> RD1, in the relationship between the background noise level change width ND2 and the sound level parameter LP2, LP2 <ND2, that is, the sound level parameter becomes smaller than the background noise level change width. . This configuration reduces the absolute output sound level by reducing the degree of decrease in the output sound level in an environment where the fluctuation range of the background noise level is large and the background noise level decreases to a very small value. It is effective in preventing the phenomenon that it becomes difficult to hear after passing.

  By the way, in the present embodiment, when the background noise level is lowered, both the frequency characteristic of the output audio signal and the audio level are controlled, but only the audio level may be controlled.

  Further, when the background noise level decreases, the voice level may be controlled first, and when the background noise level further decreases, the frequency characteristics may be further controlled.

  Further, when the background noise level decreases, the frequency characteristics may be controlled first, and when the background noise level further decreases, the audio level may be further controlled.

  As described above, the audio signal processing apparatus according to the present invention controls the frequency characteristics of the output audio signal in accordance with the background noise level over a long time, and attenuates the low-frequency signal particularly when the background noise level is reduced. Therefore, sound leakage to the surroundings can be reduced, and the high frequency signal can be attenuated in accordance with the attenuation amount of the low frequency signal, so that the ease of listening to the sound can be maintained.

  In addition, the audio signal processing apparatus of the present invention controls the output audio level in accordance with the background noise level over a long period of time, and maintains the difference between the output signal level and the background noise level when the listener sets the volume. By doing so, particularly when the ambient noise level is lowered, the output sound level is lowered at the same time, thereby reducing sound leakage to the surrounding environment and maintaining the ease of listening to the sound.

  Although the present invention has been described based on the first embodiment and the second embodiment, it is needless to say that the present invention is not limited to the above embodiment. The following cases are also included in the present invention.

  (1) Each of the above devices is specifically a computer system including a microprocessor, a ROM, a RAM, a hard disk unit, a display unit, a keyboard, a mouse, and the like. A computer program is stored in the RAM or hard disk unit. Each device achieves its functions by the microprocessor operating according to the computer program. Here, the computer program is configured by combining a plurality of instruction codes indicating instructions for the computer in order to achieve a predetermined function.

  (2) A part or all of the constituent elements constituting each of the above-described devices may be configured by one system LSI (Large Scale Integration). The system LSI is a super multifunctional LSI manufactured by integrating a plurality of components on one chip, and specifically, a computer system including a microprocessor, a ROM, a RAM, and the like. . A computer program is stored in the RAM. The system LSI achieves its functions by the microprocessor operating according to the computer program.

  (3) Part or all of the constituent elements constituting each of the above devices may be configured from an IC card that can be attached to and detached from each device or a single module. The IC card or the module is a computer system including a microprocessor, a ROM, a RAM, and the like. The IC card or the module may include the super multifunctional LSI described above. The IC card or the module achieves its function by the microprocessor operating according to the computer program. This IC card or this module may have tamper resistance.

  (4) The present invention may be the method described above. Further, the present invention may be a computer program that realizes these methods by a computer, or may be a digital signal composed of the computer program.

  The present invention also provides a computer-readable recording medium such as a flexible disk, hard disk, CD-ROM, MO, DVD, DVD-ROM, DVD-RAM, BD (Blu-ray Disc). ), Recorded in a semiconductor memory or the like. Further, the digital signal may be recorded on these recording media.

  The present invention may also be such that the computer program or the digital signal is transmitted via an electric communication line, a wireless or wired communication line, a network represented by the Internet, data broadcasting, or the like.

  The present invention may be a computer system including a microprocessor and a memory, wherein the memory stores the computer program, and the microprocessor operates according to the computer program.

  In addition, the program or the digital signal is recorded on the recording medium and transferred, or the program or the digital signal is transferred via the network or the like, and is executed by another independent computer system. It is good.

  (5) The above embodiment and the above modifications may be combined.

  The audio signal processing device of the present invention can be used in a television and radio receiver, a music playback device including a compact disc and a semiconductor memory, a video / audio playback device including a DVD and a Blu-ray disc, etc. By adapting and reproducing at the optimum sound quality volume, it is possible to achieve both ease of listening to sound and reduction of sound leakage to the surroundings.

The figure which shows the structure of the audio | voice signal processing apparatus in Embodiment 1 of this invention. The figure explaining operation | movement of the ambient noise level change detection means of this invention The figure which shows the structure of the background noise level detection means of this invention, and a frequency characteristic parameter calculation means. The figure which shows an example of the frequency characteristic implement | achieved by the frequency characteristic parameter of this invention The figure which shows the structure of the audio | voice signal processing apparatus in Embodiment 2 of this invention. The figure which shows an example of the relationship between the background noise level of this invention, and an output audio | voice level The figure which shows another example of the relationship between the background noise level of this invention, and an output audio | voice level

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Silent part detection means 102 Ambient audio signal detection means 103 Ambient noise signal detection means 104 Ambient noise level change detection means 105 Background noise level detection means 106 Frequency characteristic parameter calculation means 107 Frequency characteristic control means 108 Characteristic control means 109 Audio output means 301 Switch means 302 Energy calculation means 303 Energy value smoothing means 304 Energy value buffer means 305 Low-frequency attenuation parameter calculation means 306 High-frequency attenuation parameter calculation means 501 Audio level parameter calculation means 502 Audio level control means

Claims (12)

Ambient sound signal detection means for detecting ambient sound signals in the acoustic space;
A silent part detecting means for detecting a silent part of the input audio signal;
Ambient noise signal detection means for detecting an ambient noise signal that is the ambient audio signal in the silent part;
Ambient noise level change detecting means for detecting a level change of the ambient noise signal;
A background noise level detecting means for detecting a background noise level which is a level of the ambient noise signal when a level change of the ambient noise signal is small;
An audio signal processing device comprising: characteristic control means for controlling the characteristics of the input audio signal based on the background noise level and outputting an audio output signal for output to the acoustic space. Ambient sound level detection means for detecting an ambient sound level that is the level of an ambient sound signal in the acoustic space;
A silent part detecting means for detecting a silent part of the input audio signal;
Ambient noise level detection means for detecting an ambient noise level that is the ambient voice level in the silent part;
Ambient noise level change detecting means for detecting a change in the ambient noise level;
Background noise level detection means for detecting a background noise level that is the ambient noise level when the change in the ambient noise level is small;
An audio signal processing device comprising: characteristic control means for controlling the characteristics of the input audio signal based on the background noise level and outputting an audio output signal for output to the acoustic space. The audio signal processing apparatus according to claim 1, wherein the characteristic control unit performs control so as to attenuate a low frequency of the input audio signal as the background noise level decreases. The audio signal processing apparatus according to claim 3, wherein the characteristic control unit performs control so as to further attenuate a high frequency range of the input audio signal as the background noise level decreases. The audio signal processing apparatus according to claim 1, wherein the characteristic control unit performs control so as to decrease a volume of the input audio signal as the background noise level decreases. 3. The control according to claim 1, wherein the characteristic control unit performs control so as to decrease a volume of the input audio signal and attenuate a low frequency of the sound source signal as the background noise level decreases. Audio signal processing device. The characteristic control means controls the input sound signal to decrease in volume as the background noise level decreases in a predetermined range, and to further attenuate a low frequency range of the sound source signal in a range smaller than the predetermined range. The audio signal processing device according to claim 6. 6. The audio signal processing apparatus according to claim 5, wherein the characteristic control means controls the volume of the input audio signal to be changed by the change in the background noise level. The audio signal processing apparatus according to claim 5, wherein the characteristic control unit controls the volume of the input audio signal to change less than a change in the background noise level. Detecting ambient audio signals in the acoustic space;
Detecting a silent portion of the input audio signal;
Detecting an ambient noise signal that is the ambient audio signal in the silent portion;
Detecting a level change of the ambient noise signal;
Detecting a background noise level that is a level of the ambient noise signal when a level change of the ambient noise signal is small;
Controlling the characteristics of the input audio signal based on the background noise level and outputting an audio output signal for output to the acoustic space. Detecting an ambient audio level that is a level of an ambient audio signal in the acoustic space;
Detecting a silent portion of the input audio signal;
Detecting an ambient noise level that is the ambient audio level in the silent portion;
Detecting a change in the ambient noise level;
Detecting a background noise level that is the ambient noise level when the change in the ambient noise level is small;
Controlling the characteristics of the input audio signal based on the background noise level and outputting an audio output signal for output to the acoustic space. The program for making a computer perform each step contained in the audio | voice signal processing method of Claim 10 or Claim 11.

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