JPH09232896A - Audio signal processing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To always listen to music by the same frequency balance. SOLUTION: The frequency division into two bands or more is performed for an audio signal, the compressibility of each frequency band is determined based on a loudness characteristic and a compressor 4 compresses, synthesizes and outputs the audio signal of each frequency band for which the frequency division is performed based on the compressibility. Based on the relation of the size of the ruing noise according to the loudness characteristic and running speed and the frequency, the compressibility of each frequency band in the present running speed is determined and the audio signal of each frequency band for which the frequency division is performed is compressed, synthesized and outputted based on the compressibility. Further, based on the maximum value of listening sound by the loudness characteristic and volume, the compressibility of each frequency band is determined, and the audio signal of each frequency band for which the frequency division is performed is compressed, synthesized and outputted based on the compressibility.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio signal processing method for outputting a predetermined sound quality control process to an audio signal and outputting the audio signal, and in particular, even when the maximum listening level changes or running noise changes. Even if the ratio of the dynamic range of the predetermined frequency band and the dynamic range of the reference band before and after the change is the same, it is an object of the present invention to provide an audio signal processing method capable of always listening to music with the same frequency balance.

[0002]

2. Description of the Related Art The unit of "loudness" that humans perceive is sone, and the loudness of a pure tone of 1 kHz and 40B is 1 sone. The loudness of sound perceived by a human decreases sharply as the sound intensity approaches the minimum audible value, and the degree of the decrease also depends on the noise level. Furthermore, the loudness changes not only with the strength of the sound but also with the frequency spectrum. FIG. 12 shows a state in which there is no external noise and the sound pressure level is 1 dB at x dB (x = 5 to 130 dB).
It is called the equal loudness curve by connecting the sound pressure levels of pure tones with the same loudness as Hz pure tones. As is clear from FIG. 12, the increase rate of loudness is higher in the bass range and the treble range than in the middle range. That is, if the sound level changes uniformly over all frequencies, the relative loudness of each frequency component changes, and the sound balance is lost. For this reason, the conventional audio apparatus is provided with a loudness circuit that raises the volume in the low range and the high range according to the aperture amount when the volume is reduced.

[0003]

However, since the conventional loudness circuit does not take measures against the dynamic range, when the maximum value of the listening level changes, the dynamic range at each frequency changes individually, and the frequency band changes. The overall balance is lost and it becomes difficult to listen to music, etc. FIG.
FIG. 3 is a loudness curve explanatory diagram showing how the dynamic range changes. As is clear from this loudness curve, the dynamic range differs depending on the frequency. For example, if the maximum listening level is 100 dB, then 1 k
The dynamic range of Hz is 100 dB, and the dynamic range of 100 Hz is 80 dB. If the maximum value of the listening level is 80 dB, the dynamic range of 1 kHz is 80 dB and the dynamic range of 100 Hz is 60 dB. Therefore, if the maximum listening level is changed from 100 dB to 80 dB depending on the volume, the dynamic range ratio between 1 kHz and 100 Hz changes from 0.8 to 0.75, as shown in FIG. Become. The above is the case of 1 kHz and 100 Hz, but the dynamic range ratio changes over all frequencies.

In the case of an on-vehicle audio system, noise is generated depending on the vehicle speed. The driving noise is louder in the lower range and is above the minimum audible level. Therefore, the audio voice is masked by the running noise, the minimum audible curve changes, and the dynamic range of each frequency changes. Conventionally, since the change in the dynamic range due to such running noise is not considered, the balance of the entire frequency band is lost depending on the vehicle speed, and it becomes difficult to listen to music.

In view of the above, a first object of the present invention is to provide an audio signal processing method capable of listening to music with the same frequency balance as live performance. A second object of the present invention is to make the ratio of the dynamic range of each frequency band and the dynamic range of the reference band before and after the change the same even if the running noise changes and the dynamic range of each frequency band changes. It is an object to provide an audio signal processing method capable of always listening to music with the same frequency balance. A third object of the present invention is to make the ratio of the dynamic range of each frequency band and the dynamic range of the reference band the same before and after the change even if the maximum value of the listening level changes due to volume operation or the like, and always the same. An object of the present invention is to provide an audio signal processing method capable of listening to music with frequency balance.

[0006]

According to the present invention, the first object is to frequency-divide an audio signal into two or more bands, each of which is based on a loudness characteristic of a sound perceived by a person according to the frequency. This is achieved by an audio signal processing method in which the compression ratio of the frequency band is determined, the frequency-divided audio signal of each frequency band is compressed based on the compression ratio, and the compressed signals are combined and output.
(Claim 1) According to the present invention, the second object is to convert the audio signal into two.
The frequency is divided into the above bands, and the compression ratio of each frequency band at the current running speed is based on the loudness characteristics of the sound perceived by humans according to the frequency and the relationship between the running noise level and the frequency according to the running speed. Is determined, and the frequency-divided audio signal of each frequency band is compressed based on the compression rate, and the compressed signal is synthesized and output.
... Claim 2

According to the present invention, the third object is that the audio signal is frequency-divided into two or more bands and is based on the loudness characteristic of the sound perceived by humans according to the frequency and the maximum value of the listening level due to the volume. And a compression ratio of each frequency band is determined, the frequency-divided audio signal of each frequency band is compressed based on the compression ratio, and the compressed signal is synthesized and output by an audio signal processing method. . According to the present invention, each of the above objects is frequency-divided into two or more bands, and a loudness characteristic of a sound perceived by a human according to the frequency, and a running noise of a running noise according to a running speed. The compression ratio of each frequency band at the current running speed is determined based on the relationship between the size and the frequency and the maximum listening level due to the volume, and the frequency-divided audio signal of each frequency band is compressed based on the compression ratio. , An audio signal processing method that synthesizes and outputs compressed signals. ... Claim 4

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION

(A) First embodiment (a) Outline The maximum value of the music listening level of a live performance is generally about 100 dB [S
PL]. If the audio signal can be reproduced with the same maximum level and dynamic range as this, there is no problem. However, in reality, the maximum value is at most about 80 dB [SPL] due to environmental problems such as neighborhood noise and the problem that a system capable of reproducing the volume up to this point as an audio device becomes very large and expensive. Now, when performing live, comparing the ratio of the dynamic range of 1 kHz / 100 Hz with the maximum value of 100 dB “SPL” and the ratio of the dynamic range of 1 kHz / 100 Hz with the maximum value of 80 dB “SPL”, as shown in FIG. That is, the dynamic range ratio when the maximum value is 100 dB is 0.8, and the dynamic range ratio when the maximum value is 80 dB is 0.75.

To listen to music with the same dynamic range ratio as in live performance, the dynamic range ratio should be the same. To make the dynamic range ratio the same value (= 0.8), the dynamic range of 100Hz at the maximum value of 80dB should be 64dB. However, since it has the minimum audible characteristic, the sound below the minimum audible characteristic cannot be heard. Therefore, 64dB should be compressed to 60dB. Compression rate τ
Is given by the following equation τ = 0.75 / 0.80 (= 60/64) = 0.9375. By applying compression of this compression rate τ, the dynamic range becomes equal to 64 dB, the dynamic range ratio becomes 64/80 = 0.8, which is the same as the 1 kHz dynamic range ratio, and the music is played with the same frequency balance as the live performance. Can be heard.

(B) Configuration FIG. 1 is a configuration diagram of a first embodiment of the present invention, in which 1 is a low frequency boost circuit for boosting a low frequency component of an audio signal,
2 is a low-pass filter that passes the low frequency band of the audio signal, 3 is a high-pass filter that passes the high frequency band component of the audio signal, 4 is a compressor (COMP) that compresses the low frequency band component of the audio signal, and 5 is the output signal of the compressor 4. And the output signal of the high pass filter 3 are combined. FIG. 2 is an explanatory diagram of the compressor / expander. The compression rate (expansion rate) τ is defined by τ = (output level) / (input level), and 0 <τ <1 results in compression (compressor) and τ> 1 results in expansion (expander). Therefore, the compression rate and the expansion rate are the slopes of the straight lines CL and EL shown in FIG. 2, respectively.

Now, referring to the equal loudness curve of FIG. 12, it is about 200 Hz that the equal sensitivity level changes abruptly.
It is near. Therefore, the cutoff frequency fc of the low pass filter 2 and the high pass filter 3 is set to about 200 Hz. Also, in order to listen to music with the same frequency balance as live performance, it is sufficient to compress the low frequency component with a compression ratio of 0.9375. Therefore, the compressor 4 compresses the output signal of the low-pass filter 2 at a compression rate of 0.9375. From the above,
The ratio of the dynamic range of the low frequency component of 200 Hz or less and the high frequency component of 200 Hz or more becomes the same as the dynamic range ratio of the live performance, and if you listen to music based on the audio signal synthesized by the synthesis circuit 5, the live performance You can listen to music with the same frequency balance.

(C) Modified Example (c-1) First Modified Example In the first embodiment shown in FIG. 1, the compressor 4 is composed of an analog circuit, but it is composed of a digital circuit such as a DSP (digital signal processor). You can also In such a case, the compression takes time td. Therefore, it is necessary to delay the output of the high pass filter 2 by td to match the signal phase. FIG. 3 shows an example in which the compressor 4 is configured by a DSP, and the same parts as those in FIG. 1 are designated by the same reference numerals. A delay circuit 6 delays the time td required for the compression process.

(C-2) Second Modification In the first embodiment shown in FIG. 1, the audio signal is divided into two frequency bands, a low frequency band of 200 Hz or lower and a high frequency band of 200 Hz or higher. ≧ 3) divided into frequency bands, dynamic range and 1k in each frequency band
The Hz dynamic range ratio may be the same as the live range dynamic range ratio.
FIG. 4 shows a modified example of the first embodiment in such a case, 11 is a low frequency booster or equalizer, and 12 to 15 are first to first.
Filters having passbands in the fourth frequency band
(Low pass, band pass, high pass filter), 16 to 1
9 is the dynamic range and 1 kHz in each frequency band
Compressors (COMP1-COMP) that apply predetermined compression to the output of each filter so that the ratio of the dynamic range of z becomes the same value as the dynamic range ratio during live performance.
4) and 20 are combining circuits for combining the outputs of the respective compressors. According to this modified example, since the dynamic range ratio in each frequency band can be made extremely fine and equal to that in the live performance, it is possible to listen to music with the same frequency balance as in the live performance.

(B) Second Embodiment (a) Outline When a vehicle runs, running noise (engine noise, etc.) is generated.
This running noise becomes louder in the lower range and becomes louder as the running speed becomes higher. Figure 5 shows the loudness curve
The graph shows the relationship between running noise and frequency during idling / 20km / H driving / 60km / H driving. As is clear from this figure, the running noise level is above the minimum audible level. As a result, the audio voice is masked by the running noise, the minimum audible curve changes, and the dynamic range of each frequency changes. FIG. 6 is an explanatory diagram of the dynamic range, the dynamic range ratio, and the compression rate at 1 kHz and 100 Hz with or without running noise (running speed) at the maximum volume of 100 dB "SPL". As is clear from Fig. 5,
The dynamic range at 1 kHz and 100 Hz changes, as shown in FIG. As a result, the dynamic range ratio at 1kHz, 100Hz at no running noise (when silent), idling, 20km / H running, 60km / H running is:
They are 0.80, 0.64, 0.44 and 0.45 respectively.

Therefore, in order to listen to music at the time of idling and each running at the same dynamic range ratio (= 0.8) of 1 kHz and 100 Hz in the silent state, the same idea as in the first embodiment is used. It is only necessary to compress an audio signal of 100 Hz, and the compression ratios of each are τ ₁ = 0.64 / 0.8 = 0.80 τ ₂ = 0.44 / 0.8 = 0.55 τ ₃ = 0.45 / 0.8 = 0.56.

(B) Configuration FIG. 7 is a configuration diagram of a second embodiment of the present invention, in which 1 is a low frequency boost circuit for boosting a low frequency component of an audio signal,
2 is a low-pass filter that passes a low frequency band of 200 Hz or less of the audio signal, 3 is a high-pass filter that passes a high frequency component of the audio signal of 200 Hz or higher, 4 is a compressor (COMP) that compresses the low frequency component of the audio signal, 5 Is a synthesizing circuit for synthesizing the output signal of the compressor 4 and the output signal of the high-pass filter 3, 21 is an engine rotation detecting sensor for detecting the rotation of the engine, 22 is a vehicle speed sensor for detecting the traveling speed of the vehicle, and 23 is in accordance with the traveling state. Is a compression ratio control unit that determines the compression ratio and outputs it to the compressor 4, and compresses according to the quiet time, idling time, 20km / H running, 40km / H running, 60km / H running ... A table for preliminarily calculating and storing the rate τ is provided, and the compression rate according to the current running state is obtained and input to the compressor 4.

The audio signal whose low band has been raised by the low band booster 1 is input to a low pass filter 2 and a high pass filter 3 where it is separated into low band and high band components, and the low band component is fed to a compressor 4 and a high band component. The components are input to the synthesis circuit 5. In parallel with the above, the compression rate control unit 23 recognizes the traveling state of the vehicle based on the detection signals of the engine rotation detection sensor 21 and the vehicle speed sensor 22, obtains the compression rate τ corresponding to the traveling state from the table, and compresses the compressor. Enter in 4. The compressor 4 subjects the input low frequency audio signal to compression processing with a compression rate τ and inputs the compressed signal to the addition circuit 5,
The adder circuit 5 combines the signals input from the high-pass filter 3 and the compressor 4 and outputs the combined signal. Due to the above, even if the running condition changes, 200 Hz or lower low frequency components and 200 H
The ratio of the dynamic range of high frequency components of z or higher can be made equal to the dynamic range ratio at the time of silent, so that the music can be heard with the same frequency balance as at the time of silent regardless of the running condition.

(C) Modification (c-1) First Modification In the above description, the compressor 4 is composed of an analog circuit. However, when the compressor 4 is composed of a DSP, the output side of the high-pass filter 3 is provided. It is necessary to provide a delay circuit and delay the DSP compression processing time to match the phases. Further, in the above description, the engine rotation detection sensor 21 / vehicle speed sensor 22 is provided, but instead of these, the noise detection unit 24 is provided, and the relationship between the traveling noise level and the compression rate is provided in a table in advance, and the traveling noise is obtained. It can also be configured to obtain a higher compression rate.

(C-2) Second Modification In the second embodiment of FIG. 7, the audio signal is divided into two frequency bands, a low frequency band of 200 Hz or less and a high frequency band of 200 Hz or more. ≧ 3) divided into frequency bands, dynamic range and 1k in each frequency band
It is also possible to configure the ratio of the dynamic range of Hz to be the same value even when the running state changes. FIG. 8 shows a modification of the second embodiment in such a case, and the same parts as those in FIG. 7 are designated by the same reference numerals. 31 to 34 are filters (low-pass, band-pass, and high-pass filters) whose pass bands are the first to fourth frequency bands, and 35 to 38 are the ratios of the dynamic range in each frequency band and the dynamic range of 1 kHz in the running state. Compressors (COMP1 to COMP4) for applying a predetermined compression to the respective filter outputs so that the same values will be obtained even if they change, 39 is a synthesizing circuit for synthesizing the respective compressor outputs. Compressibility control unit 23
In the table (not shown), for each frequency band, silent, idling, 20 km / H running, 40 km / H running, 60
When traveling at km / H, the compression ratio τ corresponding to ... is calculated and stored in advance.

The audio signals whose low frequencies have been raised by the low frequency booster 1 are input to the filters 31 to 34, frequency-divided therein, and then input to the compressors 35 to 38, respectively. In parallel with the above, the compression rate control unit 23 recognizes the running state of the vehicle based on the detection signals of the engine rotation detection sensor 21 and the vehicle speed sensor 22, and compresses τ ₁ to τ ₄ is obtained from the table and input to the compressors 35-38. The compressors 35 to 38 perform the compression processing of the compression ratios τ _{1 to} τ _{4 on} the input audio signals of the respective frequency bands and input them to the adder circuit 29.
The signals input from 8 are combined and output. According to this modification, the dynamic range ratio in each frequency band can be made extremely fine and can be made equal to that in silent time, so that music can be heard with the same frequency balance as in silent time.

(C) Third Embodiment (a) Outline As is clear from FIG. 13, when the maximum value of the listening level is changed by the volume, the dynamic range of each frequency band changes. That is, the maximum listening level is 100
Assuming dB, the dynamic range of 1 kHz is 100
The dynamic range of dB and 100 Hz is 80 dB. If the maximum listening level is 80 dB, then 1k
The dynamic range of Hz is 80 dB, and the dynamic range of 100 Hz is 60 dB. Therefore, if the maximum listening level is changed from 100 dB to 80 dB depending on the volume, as shown in FIG. 14, 1 kHz and 100 Hz
The dynamic range ratio of changes from 0.8 to 0.75, the balance is lost and it becomes difficult to listen to music.

FIG. 9 shows 1k for the maximum sound volume of 60 to 120 dB "SPL".
It is explanatory drawing of the dynamic range, dynamic range ratio, and compression rate in Hz and 100 Hz. 1kHz depending on the maximum volume,
The dynamic range at 100 Hz changes, as shown in FIG. As a result, 1kHz, 100Hz at maximum listening level (volume position) of 60dB, 80dB, 100dB, 120dB
The dynamic range ratios are 0.67, 0.75, 0.
It becomes 80, 0.83. Therefore, 1k at maximum level 100dB
In order to listen to music at each maximum listening level with the same dynamic range ratio as Hz and 100 Hz, it is sufficient to compress the 100 Hz audio signal according to the same idea as in the first embodiment. (Expansion rate) is τ ₁ = 0.67 / 0.8 = 0.8375 τ ₂ = 0.75 / 0.8 = 0.9375 τ ₃ ＝ 0.8 / 0.8 = 1.0 τ ₄ ＝ 0.8 ₃ /0.8=1.0 ₃₇₅

(B) Configuration FIG. 10 is a configuration diagram of a third embodiment of the present invention, in which 1 is a low frequency boost circuit for boosting a low frequency component of an audio signal, and 2 is a low frequency of 200 Hz or less of the audio signal. A low-pass filter that passes 3 is a high-pass filter that passes high-frequency components of 200 Hz or higher of the audio signal, 4 is a compressor (COMP) that compresses low-frequency components of the audio signal, and 5
Is a synthesizing circuit for synthesizing the output signal of the compressor 4 and the output signal of the high-pass filter 3, 41 is a volume, 51 is a compression rate control unit that determines the compression rate according to the volume position (maximum listening level) and outputs it to the compressor 4. And
Compression ratio τ according to each maximum listening level 60 dB ~ 120 dB (Fig. 9)
Is pre-calculated and stored, and the compression ratio τ according to the current maximum listening level is calculated and input to the compressor 4.

The audio signal whose low band has been raised by the low band booster 1 is input to the low pass filter 2 and the high pass filter 3, where it is separated into low band and high band components, and the low band component is fed to the compressor 4 and high band. The components are input to the synthesis circuit 5. In parallel with the above, the compression rate control unit 42 determines the compression rate τ according to the maximum listening level set by the volume 41.
Is obtained from the table and input to the compressor 4. The compressor 4 subjects the input low frequency audio signal to compression processing with a compression ratio τ and inputs the compressed signal to the adder circuit 5, where the adder circuit 5
Synthesizes the signals input from the high-pass filter 3 and the compressor 4 and outputs the synthesized signal. As described above, even if the maximum listening level changes depending on the volume, the ratio of the dynamic range of the low frequency component of 200 Hz or less and the high frequency component of 200 Hz or more can be made the same as the dynamic range ratio at the maximum listening level of 100 dB. With a dynamic range ratio of 100 dB, that is, you can always listen to music with the same frequency balance.

(C) Modification In the above, the audio signal is set to a low frequency band of 200 Hz or less,
This is a case of dividing into two high frequency bands of 200 Hz or more, but dividing into n (≧ 3) frequency bands and changing the maximum listening level by the ratio of the dynamic range and the dynamic range of 1 kHz in each frequency band. However, they can be configured to be the same.

(D) Fourth Embodiment In the second embodiment, only the traveling state is considered, and in the third embodiment, only the volume position (maximum listening level) is considered. However, both are considered and the traveling state is considered. Even if changes,
1k in each frequency band even if the maximum listening level changes
It is also possible to configure the dynamic range ratio of Hz and 100 Hz to be a constant value. FIG. 11 is a configuration diagram of an embodiment in such a case, in which the frequency band is 200 Hz or lower and 200 Hz or less.
This is the case of being divided into the above two high frequencies, and the same parts as those in the second embodiment of FIG. 7 and the third embodiment of FIG. 10 are designated by the same reference numerals.

Reference numeral 1 is a low-pass boost circuit for boosting a low-frequency component of an audio signal, 2 is a low-pass filter that passes a low-frequency component of the audio signal of 200 Hz or less, and 3 is a high-pass that passes a high-frequency component of the audio signal of 200 Hz or more. A filter 4, a compressor (COMP) for compressing low frequency components of an audio signal, 5 a synthesizing circuit for synthesizing an output signal of the compressor 4 and an output signal of the high-pass filter 3, 21 an engine rotation detecting sensor for detecting engine rotation Two
Reference numeral 2 is a vehicle speed sensor for detecting the traveling speed of the vehicle, 41 is a volume, 51 is a compression ratio control unit that determines the compression ratio according to the traveling state / volume position (maximum listening level) and outputs it to the compressor 4. When idling,
20km / H running, 40km / H running, 60km / H running, ... Maximum listening level 60dB ~ 12 in each running condition
A table 51a for pre-calculating and storing a compression rate τ corresponding to 0 dB is provided, and the compression rate corresponding to the current running state and the current maximum listening level is obtained from the table and input to the compressor 4.

The audio signal whose low band has been raised by the low band booster 1 is input to a low pass filter 2 and a high pass filter 3, where it is separated into a low band component and a high band component, and the low band component is fed to a compressor 4 and a high band component. The components are input to the synthesis circuit 5. In parallel with the above, the compression rate control unit 51 recognizes the current running state of the vehicle based on the detection signals of the engine rotation detection sensor and the vehicle speed sensor, and the volume 41
Recognize the current maximum listening level based on the position of. Then, the compression rate control unit 51 obtains the compression rate τ according to the current traveling state and the current maximum listening level from the table 51a and inputs it to the compressor 4. The compressor 4 subjects the input low frequency audio signal to compression processing with a compression rate τ and inputs it to the adder circuit 5. The adder circuit 5 combines the signals input from the high-pass filter 3 and the compressor 4 and outputs the combined signal.
From the above, even if the running state and the maximum listening level change, the ratio of the dynamic range of the low frequency component of 200 Hz or less and the high frequency component of 200 Hz or more can be made the same as the dynamic range ratio of 100 dB at the silent time. You can listen to music with the same frequency balance regardless of the maximum listening level.

In the above description, the audio signal is divided into two frequency bands, a low frequency band of 200 Hz or lower and a high frequency band of 200 Hz or higher. However, the audio signal is divided into n (≧ 3) frequency bands and each frequency band is divided into two frequency bands. Dynamic range and 1
The dynamic range ratio of kHz may be configured to be the same even when the running state / maximum listening level changes. As described above, the present invention has been described with reference to the embodiments. However, the present invention can be variously modified in accordance with the gist of the present invention described in the claims, and the present invention does not exclude these.

[0030]

As described above, according to the present invention, the audio signal is frequency-divided into two or more bands, and the compression ratio of each frequency band is determined based on the loudness characteristic of the sound perceived by humans according to the frequency. Since the frequency-divided audio signal of each frequency band is compressed based on the compression ratio and the compressed signals are combined and output, the music can be heard with the same frequency balance as the live performance. According to the present invention, an audio signal is frequency-divided into two or more bands, and based on the characteristics of the loudness of sound perceived by humans according to the frequency and the relationship between the magnitude of the running noise and the frequency according to the running speed, The compression rate of each frequency band at the current traveling speed is determined, the frequency-divided audio signal of each frequency band is compressed based on the compression rate, and the compressed signals are combined and output. Even if the noise changes and the dynamic range of each frequency band changes, the ratio of the dynamic range of each frequency band and the dynamic range of the reference band before and after the change can be made the same, and always listen to music with the same frequency balance. Can be done.

According to the present invention, the audio signal is frequency-divided into two or more bands, and the frequency band of each frequency band is based on the loudness characteristic of the sound perceived by humans according to the frequency and the maximum value of the listening level due to the volume. The compression ratio is determined, the frequency-divided audio signals in each frequency band are compressed based on the compression ratio, and the compressed signals are combined and output. Even if the value changes, the ratio of the dynamic range of each frequency band and the dynamic range of the reference band before and after the change can be made the same, and music can always be listened to with the same frequency balance.

According to the present invention, the audio signal is frequency-divided into two or more bands, the loudness characteristic of the sound perceived by humans according to the frequency, the relationship between the loudness and frequency of the running noise according to the running speed, and the volume. Based on the maximum value of the listening level by, the compression rate of each frequency band at the current traveling speed is determined, the frequency-divided audio signal of each frequency band is compressed based on the compression rate, and each compressed signal is synthesized. Therefore, the ratio of the dynamic range of each frequency band and the dynamic range of the reference band can be made to be the same regardless of the running state and the maximum listening level, and the music can be heard with the same frequency balance.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a first embodiment.

FIG. 2 is an explanatory diagram of a compressor / expander.

FIG. 3 is a modification of the first embodiment.

FIG. 4 is another modification of the first embodiment.

FIG. 5 is a schematic explanatory diagram of a second embodiment.

FIG. 6 is a diagram for explaining a dynamic range, a dynamic range ratio, and a compression ratio depending on the presence or absence of running noise at a maximum volume of 100 dB.

FIG. 7 is a configuration diagram of a second embodiment.

FIG. 8 is a modification of the second embodiment.

FIG. 9 is an explanatory diagram of a dynamic range, a dynamic range ratio, and a compression rate with respect to the maximum volume.

FIG. 10 is a configuration diagram of a third embodiment.

FIG. 11 is a configuration diagram of a fourth embodiment.

FIG. 12 is an explanatory diagram of an equal loudness curve.

FIG. 13 is an explanatory diagram of changes in dynamic range.

FIG. 14 is a chart for explaining a dynamic range and a dynamic range ratio.

[Explanation of symbols]

 1 Low-pass booth and circuit 2 Low-pass filter 3 High-pass filter 4 Compressor 5 Synthesis circuit

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location H03G 5/16 H03G 5/16 Z

Claims (4)

[Claims] 1. An audio signal processing method for applying a predetermined sound quality control process to an audio signal and outputting the audio signal, wherein the audio signal is frequency-divided into two or more bands, and a loudness characteristic of sound perceived by a human being is obtained according to the frequency. An audio signal processing characterized in that the compression ratio of each frequency band is determined based on the compression ratio, the frequency-divided audio signal of each frequency band is compressed based on the compression ratio, and the compressed signals are combined and output. Method. 2. An audio signal processing method for applying a predetermined sound quality control process to an audio signal and outputting the audio signal, wherein the audio signal is frequency-divided into two or more bands, and a loudness characteristic of sound perceived by a human being in accordance with the frequency. The compression ratio of each frequency band at the current traveling speed is determined based on the relationship between the running noise level and the frequency according to the running speed, and the frequency-divided audio signal of each frequency band is compressed based on the compression ratio. Then, the compressed audio signals are combined and output. 3. An audio signal processing method for applying a predetermined sound quality control process to an audio signal and outputting the audio signal, wherein the audio signal is frequency-divided into two or more bands, and a loudness characteristic of a sound perceived by a human being in accordance with the frequency. The compression ratio of each frequency band is determined based on the maximum listening level by the volume, the frequency-divided audio signal of each frequency band is compressed based on the compression ratio, and each compressed signal is combined and output. An audio signal processing method characterized by the above. 4. An audio signal processing method for applying a predetermined sound quality control process to an audio signal and outputting the audio signal, wherein the audio signal is frequency-divided into two or more bands, and a loudness characteristic of sound perceived by a human being in accordance with the frequency, The compression ratio of each frequency band at the current driving speed is determined based on the relationship between the running noise level and the frequency according to the running speed and the maximum value of the listening level by the volume, and the audio signal of each frequency divided frequency band is determined. An audio signal processing method, comprising: compressing based on the compression rate; combining the compressed signals and outputting the combined signals.