JPH06319192A - Audio signal processing method/device - Google Patents

Abstract

PURPOSE:To provide a noise adaptive signal processor which can always perform the adjustment of sound volume and the correction of frequency for the reproduced audio signals with no feeling of incongruity despite both the change of the output sound volume level and the change of frequency characteristics of reproduced sounds. CONSTITUTION:An audio signal processor is provided with a noise adaptive signal processing means. This signal processing means estimates the levels of noises detected in a car and the running noise levels that are felt by a listener from the car running speed signal. Then the signal processing means increases the sound volumes and the dynamic range of the reproduced audio signal as the running noise level is increased and also increases the low frequency sound band component level of the reproduced audio signal as the low frequency sound band component level is increased respectively. Then a detecting means 14 is added to the audio signal processor to detect the output sound volume level of the reproduced audio signal, together with a control means which adjusts to reduce the corrected quantity of each audio signal as the level detected by the means 14 is increased.

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 and apparatus for using a digital signal processing integrated circuit to control the sound quality and the like of car audio by adapting to background noise such as running noise.

[0002]

2. Description of the Related Art Conventionally, various noise adaptive signal processing systems have been considered which detect a vehicle running noise and control the volume level of an audio signal by using an analog circuit. Also,
A method of using digital signal processing for audio signal processing is being put to practical use.

FIG. 22 is a block circuit diagram showing a typical example of a conventional audio signal processing circuit. 1 is an audio source such as a CD player, 2 is volume adjustment, tone color adjustment,
An audio signal processing circuit for performing dynamic range compression processing, 3 is an amplifier, 4 is a speaker, and 5 is a vehicle speed signal detection circuit, which receives a vehicle speed signal from a vehicle speed sensor 6 attached to the vehicle and outputs a signal having a frequency corresponding to the vehicle speed. Send a pulse signal. A noise level detector 7 detects a noise level in the vehicle interior from a noise signal in the vehicle interior picked up by a microphone 8 installed in the vehicle interior. Reference numeral 9 is a control device composed of a microcomputer or the like, which estimates a running noise level from the detected vehicle interior noise level and vehicle speed signal, and adapts to the running noise level to control the sound quality of the volume, tone color, etc. of the audio reproduction signal. Create a control signal to perform.

Since this conventional apparatus uses both the vehicle interior noise level and the vehicle speed signal to estimate the running noise level, it is possible to more accurately estimate the running noise and perform audio signal processing. Since the digital signal processing circuit and the microcomputer are used for the processing control, the adaptive range of the noise adaptive processing is wide and the accuracy is high.

However, the running noise level estimation error due to the influence of the audio reproduction sound mixed in the microphone, and the psychoacoustic discomfort due to the relationship between the listening level of the reproduction sound and the background noise may occur. Since the relationship between the characteristics of the audio signal reproduced sound and the audibility as described below is not taken into consideration, an audible discomfort may occur depending on the form of the audio signal.

First, an outline of the acoustic phenomenon given to the perceptual sound quality will be described. The volume feeling and the sound quality are related to the volume level, frequency characteristics, background noise, and the like. FIG. 23 shows a well-known volume sensitivity (loudness) curve, and the auditory sensitivity is large in the frequency component of 1 KHz to 3 KHz and small in the bass range. However, this characteristic changes depending on the sound pressure level, the sensitivity change due to the frequency becomes small at a large volume, and the sensitivity to an increase / decrease change in the volume becomes dull at a large volume.

When a music signal and noise are present at the same time, the volume feeling of the music signal depends on the masking phenomenon due to the noise. That is, if the level of the music signal is sufficiently higher than the level of the noise in the adjacent frequency band, it can be heard without any trouble, but the volume decreases as the level of the music signal gets closer to the noise level. I feel it, and finally I cannot hear it.

Therefore, in such an audio signal processing apparatus, when the music signal level is low and the auditory masking due to noise is likely to occur, the audio signal processing apparatus performs processing so that the volume is sufficiently high, and when the music signal level is high. Must be treated so that it does not grow unnecessarily.

Further, since the traveling noise has a large component in the low frequency region, it is necessary to process the low frequency region of the music signal.

As for the degree of control change of the music signal processing, it is possible to prevent unnecessary follow-up of noise generated by unevenness of the traveling road surface or door opening / closing, and to prevent a sudden sound volume and sound quality change. In order to suppress the above discomfort, it is necessary to suppress the control appropriately.

The speed of the automobile changes faster during deceleration than during acceleration, and the running noise level also changes faster during deceleration than during acceleration. On the other hand, as for the psychology of the sense of volume, when the volume is higher than the set volume, there is a tendency to feel a great sense of discomfort. Therefore, it is necessary to make the sound quality control change degree during acceleration different from that during deceleration so that the degree of signal processing control change for deceleration is faster so that the volume level does not become excessive when the noise level is reduced due to deceleration. There is.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and noise adaptive signal processing is performed with respect to the volume characteristics and the frequency characteristics of the output sound, which change every moment when the audio is heard. It is an object of the present invention to provide an audio signal processing method and apparatus that can always achieve a function of correcting an audio output sound that does not cause discomfort.

[0013]

In the audio signal processing method according to the present invention, the volume of an audio output signal of an audio device provided in a vehicle is controlled according to the magnitude of a running noise level of the vehicle. In what I did,
The volume level of the audio output signal is detected, and the increase rate of the volume of the audio output signal is reduced as the detected volume level increases.

Further, the higher the detected sound volume level is, the smaller the increase rate of the bass component of the audio output signal is made.

Further, the higher the detected volume level, the smaller the increase rate of the waveform compression rate of the audio output signal.

Further, the higher the detected volume level is, the smaller the increase rate of the waveform compression rate of the audio output signal is made.

Further, the volume level of the audio output signal is audibly corrected, and the volume level of the audio output signal, the low frequency range component, and the increase rate of the waveform compression rate are adjusted by the corrected volume level.

The audio signal processing device according to the present invention is provided with means for correcting the volume of the audio output signal of the audio device provided in the vehicle according to the vehicle speed, and means for detecting sudden deceleration and rapid acceleration of the vehicle. Further, there is provided means for adjusting the sound quality correction rate of the audio output signal to be changed slightly later than the change of the vehicle speed when the vehicle is suddenly decelerated, and to be changed further slowly when the vehicle is suddenly accelerated.

Further, a silence period of the audio output signal or a silence period in a state close to this is detected, and this silence period is held in the reproduction signal correction state immediately before that.

[0020]

According to the present invention, when the level of the reproduced audio signal is high, the output volume is increased, the dynamic range is expanded, and the amount of boost in the bass range is suppressed.

Further, since the output volume is increased, the dynamic range is expanded, and the boost amount in the low range is corrected by the output level of the audio output signal whose audibility is corrected, the audible correction is made.

Further, the response speed of the sound quality correction operation at the time of sudden deceleration and sudden acceleration is slightly slower than the change of the vehicle speed at the time of sudden deceleration and further slower at the time of sudden acceleration. To mitigate a sudden change in the sound quality correction rate.

The silent period of the audio output signal is
Since the correction state of the audio output signal is fixed as it was just before, only noise is not greatly amplified,
Further, when the silent state is changed to the voiced state, the temporary excessive volume state does not occur.

[0024]

【Example】

Example 1. The first embodiment of the present invention will be described below. Figure 1
22 is a block circuit diagram of the first embodiment, the same reference numerals as in FIG. 22 denote the same parts, 10 is an analog-digital converter (hereinafter referred to as “A / D converter”), and 11 is a digital signal processing integrated circuit. (Hereinafter referred to as "signal processing integrated circuit") (DPS), 12 is a digital-to-analog converter (hereinafter referred to as "D / A converter"), 10, 1
The audio signal processing and reproducing system 13 is composed of 1, 12, 3, and 4, and Si is an audio signal input from the audio source 1.

The control device 9 of the first embodiment is composed of a microcomputer, 14 is a level detection circuit for detecting the output level of an audio reproduction signal, 15 is a microphone amplifier, 16 is a band division filter, and 6 ,
5, 9, 14, 8, 15, and 16 form an audio signal control system 17, Sv is a vehicle speed signal output from the vehicle speed sensor 6, and Sm is a vehicle interior noise signal output from the microphone 8.

Next, of the operation of the first embodiment, a portion different from the conventional example will be described. Audio signal Si is A
The signal is converted into a digital audio signal (hereinafter, simply referred to as “audio signal”) by the / D converter 10 and input to the signal processing integrated circuit 11. The signal processing integrated circuit 11 receives the control command from the microcomputer 9 and performs amplitude amplification processing, frequency characteristic conversion processing and waveform compression processing of the audio signal.

The microcomputer 9 mainly performs the following two processes. One is to estimate the magnitude of the running noise for each frequency band from the signal Sv input from the vehicle speed sensor 6 and the vehicle interior noise signal Sm collected by the microphone 8 installed in the vehicle interior. The other one is the signal processing integrated circuit 1 based on the estimated noise and the level of the audio reproduction signal input from the level detector 14.
Three control parameters necessary for processing the audio signal by 1; volume level control parameter (amplitude amplification factor) and frequency characteristic control parameter (bass correction factor)
And calculating the control parameter of the waveform compression rate.

FIG. 2 is a diagram showing a concrete circuit example of the level detection circuit 14, and FIG. 3 is an input / output characteristic diagram thereof. In FIG. 2, C1 is a capacitor as a low-frequency component cut filter, R1 is an input suppression resistor, Q1 is an operational amplifier, D1 is a detection diode, R2 is a filter resistor, C2 is a filter capacitor, and R3 is a feedback resistor.

The level detection circuit 14 includes a detection diode D1, a filter resistor R2 and a filter capacitor C2.
According to the time constant determined by, the audio reproduction signal amplified by the operational amplifier Q1 is detected and filtered to obtain a DC level detection signal. As shown in FIG. 3, the effective value of the input signal is up to a predetermined level. In proportion to the above, the DC output is saturated at a predetermined level or more and is clipped to a predetermined value as the input level increases.

Next, a method of adjusting each control parameter with respect to the audio signal level will be described. The final output level of the audio reproduction signal generally corresponds to the audible volume. Therefore, as shown in FIG. 4, the rate of change of the three types of signal processing parameters that should be changed in accordance with the noise level is decreased as the final output level increases. For example, regarding the control of the volume level (amplitude amplification factor), the noise change rate shown on the vertical axis of the graph is 1 when the level of the audio reproduction signal is small (-60 dB), that is, the noise increase amount and the volume level. In the case where the amount of increase is equal and the level of the audio reproduction signal is as high as 0 dB, the noise change rate is reduced to about 0.1. This volume level control characteristic is shown in FIG. The amplitude correction rate on the vertical axis with respect to the running noise level on the horizontal axis is shown by curves corresponding to large, medium, and small audio reproduction signals.

FIG. 6 shows an example of a digital signal processing flow for volume level control. This figure shows only one side of the stereo 2ch system, and the multiplier α is applied to the digitized audio signal input x _i by the multiplier Δ.
Is multiplied and y _i is output. The P terminal is an input unit that gives a multiplier as a control signal. This processing can be realized by program processing when a digital signal processing integrated circuit is used. Similar processing is performed for the other channel.

FIG. 7 is a diagram showing a bass range boost (bass range correction rate) characteristic of frequency characteristic control. The frequency characteristics may be controlled by dividing the audio frequency range into, for example, three bands, and individually controlling the amplitude of each band component. In this band, boost control is performed especially in the low-pitched range because auditory masking by running noise such as engine noise is likely to occur. FIG. 7 is a diagram showing an example of the low-range boost control characteristic.

FIG. 8 shows an example of the bass signal boost control digital signal processing flow. In the figure, □ is a delay device, and ○ is an adder. Block A is a biquad digital filter, which has multipliers a ₁ , a ₂ , a ₃ , b ₁ , b _{2 of} each multiplier.
It is possible to operate as a low-pass filter by setting to a predetermined value. The output of this filter is multiplied by the multiplier β with the control signal and then mixed with the input signal x _i in the adder Σ ₂ to obtain the output signal y _i . When a digital signal processing integrated circuit is used for this processing, it can be implemented by program processing. Similar processing is performed for the other channel.

FIG. 9 is a diagram showing an example of the waveform compression control characteristic. The waveform compression is a process of compressing a dynamic range of a music signal, that is, an amplitude of a strong phrase and a weak phrase, and is a correction process corresponding to a phenomenon that a weak phrase is masked and becomes inaudible in a noisy environment. In addition, FIG.
7 and 9, the audio signal reproduction level is high, medium,
Although the small case is shown as a graph, it goes without saying that a parameter curve corresponding to these intermediate levels may actually exist.

FIG. 10 shows an example of the flow of digital signal processing for waveform compression control. The absolute values 18, 19 of the digitized signals x _iL , x _iR of the left and right channels are compared by the comparator 20, and the larger signal is selected. The selected signal is appropriately smoothed by the time constant processing 21 and detected as a signal corresponding to the level of the audio signal. The gain calculation means 22 determines a multiplier corresponding to the required waveform compression rate from the level detection signal and the control signal γ. This multiplier is multiplied by the input signals x _iL and x _iR delayed by a predetermined amount in the delay devices 23 and 24, and multipliers 25 and 26,
Obtain the output signals y _iL and y _iR . The role of the delay devices 23 and 24 is to compensate for the time delay that is spent in the time constant processing and the gain calculation.

Next, the operation of the first embodiment shown in FIG. 1 will be described. The microcomputer 9 calculates the vehicle speed from the vehicle speed signal Sv, amplifies the vehicle interior noise signal Sm picked up by the microphone 8 by the microphone amplifier 15, and further uses the signal obtained by extracting the component for each band by the band division filter 16. The running noise level is calculated and estimated for each band. This noise estimation method is the same as the conventional example.

The microcomputer 9 recognizes the level of the output signal of the amplifier 3 which is the final output of the audio reproduction signal through the level detection circuit 14 and determines the amplitude correction rate based on the graph of FIG. That is, corresponding to the estimated running noise level n, a small correction factor α _h is set when the audio playback signal level is high, a correction factor α _m is set when the audio playback signal level is medium, and a playback signal level is set when the playback signal level is medium. When it is small, the correction factor α _l is determined as the amplitude correction factor of the audio signal and is transmitted to the signal processing integrated circuit 11 in the form of a correction parameter. In this way, since the amplitude control adapted to noise can change the correction rate according to the audio reproduction signal level, the correction processing corresponding to the so-called perceptual sound volume sensitivity characteristic as shown in FIG. In the process, it is possible to obtain an effect that it does not cause a feeling of strangeness such as a sudden change in volume that is conventionally felt.

Next, control of frequency characteristics will be described. For example, as shown in FIG. 7, the bass range correction factor is β _h , which corresponds to the level n of the bass range component of the running noise, and also depending on whether the audio reproduction signal level is large, medium, or small.
Low-range signal correction is performed by determining β _m and β _l . Also in this case, the running noise mainly corresponding to the audible sensitivity characteristic of the audible sensitivity characteristic curve shown in FIG. 23, particularly in the low frequency range, and mainly the engine noise is generated in the low frequency range, so that the hearing mask is easily masked. The correction processing effect of the audio signal is obtained.

Next, the control of waveform compression will be described.
For example, as shown in FIG. 9, the audio reproduction signal levels of high, medium, and
According to the smallness, waveform compression is determined as γ _h , γ _m , and γ _l , and waveform compression correction is performed. Regarding this, since the weak phrase of the music signal is greatly affected by the auditory masking when the level of the running noise is high, the degree of waveform compression should be increased as the level of the detected audio reproduction signal is smaller. To do. This makes it possible to enjoy music as music regardless of the noise level.

FIG. 11 is a flow chart for explaining the control operation of the microcomputer 9 of the first embodiment. The outline of the operation will be described first. The microcomputer 9 divides the output of the microphone 8 into low-range (low) and middle-range (middle) bands, and outputs two signal levels Ml and Mm from Mm and the audio signal level Am reproduced from the speaker. The noise level Nm is determined, and the gain α and the D range compression γ are determined correspondingly.
Further, the microcomputer 9 determines the noise level Nl in the bass range based on the signal Ml, and thereby determines the low boost amount β. The control amounts α, β, γ determined in this way are set to D
It is set as an SP parameter to control the volume and sound quality of the speaker voice.

Next, a description will be added according to the flow. The microcomputer 9 sets the audio signal level Am together with the microphone signal levels Ml and Mm every 0.5 seconds after the initial setting.
Take in. Here, when the conditional expression (Mm> n × Am) for considering that the noise level detection error due to the voice signal included in the microphone signal is considered to be sufficiently small is satisfied, from the Mm based on the determined calculation formula, Determine the noise level Nm. Here, n is a constant coefficient exceeding 1. On the other hand, when the above conditional expression is not satisfied, the noise level Nm is calculated from the vehicle speed Vl based on a predetermined calculation expression.

Next, the low-range noise amount Nl is calculated from the received microphone low-range signal level Ml by a predetermined calculation formula. From the midrange and bass range noise amounts Nm and Nl thus determined, the gain α, the D range compression γ, and the low boost amount β with respect to the speaker reproduction signal, which are associated in advance by experiments, are determined, and these various controls are performed. It operates to convert the quantity into a DSP parameter and then set it in the DSP.

As can be understood from the above description, according to the first embodiment, a suitable listening environment can be obtained regardless of changes in the level of running noise and the level of the audio reproduction signal.

Example 2. FIG. 12 is a block circuit diagram of the second embodiment of the present invention. The same reference numerals as those in FIG. 1 denote the same parts, and 27 denotes an auditory characteristic filter. This auditory characteristic filter has a gain frequency characteristic as shown in FIG. 13 and can be basically realized by a band pass filter circuit as shown in FIG. This corresponds to the inverse characteristic of the curve in the vicinity of the standard volume level in the volume sensitivity curve of FIG. If the level characteristic is detected after the frequency characteristic of the audio reproduction signal is corrected by this filter, the reproduction sound is grasped as a signal level corresponding to the volume sense in the sense of hearing, and noise adaptive control with less discomfort can be achieved.

Example 3. FIG. 15 is a block circuit diagram of a third embodiment of the present invention, in which the same reference numerals as those in FIG. 1 denote the same parts, respectively, 28 is a vehicle speed change estimating circuit, 29 is an acceleration volume adjusting time constant memory, and 30 is deceleration It is a volume adjustment time constant memory. Although not shown, the level detection circuit 14 and the auditory characteristic filter 27 are preferably present in practical use.

In the third embodiment, the audio signal adaptive control for the most frequent changes in running noise at the time of sudden acceleration and deceleration is performed so that the sense of discomfort is reduced. , Vehicle speed signal detection circuit 5
It is estimated that when the pulse period of the vehicle speed signal input from the vehicle is shortened at a rate equal to or higher than a predetermined rate, the acceleration is rapid, and conversely, when the pulse period is increased, the vehicle is rapidly decelerated, and a determination signal is sent to the microcomputer 9. . According to the sudden acceleration / deceleration determination signal, the microcomputer 9 sets the sound quality correction parameter based on the speed of change, which is the content of the acceleration volume adjustment time constant memory 29, during the rapid acceleration, and decelerates during the rapid deceleration. A sound quality correction parameter based on the speed of change, which is the content of the time constant memory, is determined, and the digital signal processing integrated circuit 11 is instructed that the change in the bass boost correction ratio of the audio signal is delayed relative to the change in vehicle speed.

FIG. 16 schematically shows these actions.
17 and FIG. In these figures, among the three characteristic curves, the lowermost part shows the vehicle speed, the uppermost part shows the running noise, and the central part shows the sound quality correction rate.

FIG. 16 is a diagram showing the control characteristics at the time of sudden acceleration, where the transmission time point t ₀ and the acceleration end time point are t ₁ . The main point of the operation of the third embodiment is that the change in the sound quality correction rate, in this case, the increasing speed is made slower than the change in the vehicle speed.
That is, the time t _{2 at} which the change in the sound quality correction rate ends is sufficiently delayed from t ₁ .

FIG. 17 is a diagram showing the control characteristics at the time of sudden deceleration. In this case, the correction is performed at the change (attenuation) speed of the sound quality correction rate that substantially follows the change of the vehicle speed. That is, the end time t ₂ ′ of the change in the sound quality correction rate is set to be substantially the same as t ₁ . Specifically, it is preferable that the time constant during sudden acceleration is about 1.5 to 3 times the time constant for changing vehicle speed, and the time constant during sudden deceleration is about the same as the time constant for changing vehicle speed.

FIG. 18 shows a control processing flow corresponding to vehicle speed acceleration and deceleration in the third embodiment. The microcomputer 9 first measures the vehicle speed X ₁ at a time t ₀ by a predetermined means. The measured X ₁ is stored in the memory (A) in the control unit, and after the time Δt has elapsed, the vehicle speed X ₂ is measured again. Next, the magnitudes of the values of X ₂ and A are compared. If X ₂ > A, the running condition is acceleration, X ₂ <
If A, it can be determined that the vehicle is in the deceleration state. In the acceleration state, the sound quality correction rate Δg / Δt per unit time is set to the value of T ₁ to increase the sound quality correction rate. On the other hand, if the vehicle is in the deceleration state, Δg / Δt is set to T ₂ to decrease the sound quality correction rate. Here, since T ₁ is set to be larger than T _2, it is attempted to change the sound quality correction rate gently during acceleration and promptly during deceleration, as shown in FIGS. Can be realized. Such a function can be realized by programming the microcomputer 9, and by using the means as described above, an effect of reducing a sense of discomfort due to a sudden change in sound quality correction can be obtained.

In the first and second embodiments, the sound quality correction rate is changed according to the level of the audio reproduction signal. However, in part, the following problem occurs due to the circuit configuration. There is. As understood from the graph of FIG. 4, the sound quality correction rate is basically high in the low-level signal region. Extremely low levels of this low-level signal include silent portions such as pauses in music and voice interruptions. In an ideal audio reproducing circuit, these parts are almost zero signals, and in this case, even if correction processing is performed, the zero signal state does not change, and there is no sense of discomfort in hearing.

However, in a normal reproducing circuit, signals such as electrical noise are superimposed, so that in this case, only the noise component is enhanced by the sound quality correction process, and it is inevitable that a feeling of strangeness such as noise is generated. .

Further, in the sound part following the silent part, the response of the change in the volume correction ratio in the level detection circuit 14 for detecting the level of the reproduction signal is delayed, so that a large volume reproduction state is temporarily generated and the audible feeling is generated. It is not preferable.

Example 4. The fourth embodiment of the present invention solves the above problems. FIG. 19 is a block circuit diagram of the fourth embodiment, and the same reference numerals as those in FIG. 1 denote the same parts, and 31 denotes a silence detecting circuit. In the fourth embodiment, a pause phrase or a silent portion of a voice in a music signal is detected and identified by the silence detecting circuit 31 and the micro computer 9, and when the audio signal below a predetermined level continues for a predetermined period, the noise adaptive control is suspended. It was done like this.

FIG. 20 is a diagram showing a specific circuit example of the silence detecting circuit 31. This circuit is similar to the level detecting circuit 14 for the audio reproduction signal shown in FIG. 2 and has a predetermined voltage at the subsequent stage. A comparator circuit Q4, which is an operational amplifier for comparing with, is provided, and a significant signal output, that is, a silence determination signal is obtained when the level is equal to or lower than a predetermined level.

FIG. 21 is a flow chart of the microcomputer operation in the fourth embodiment. In the figure, the process from "Silence detection?" Is the same as that in FIG. Although the gain α, the D range compression β, and the low boost γ are determined by the operation described in FIG. 11, when the audio signal level is 0, that is, in the silent state, this control parameter is not transmitted to the DSP and is temporarily held. Is the main point of this embodiment. As shown in the flow chart, a flow for determining whether or not there is a silent state is added before the parameter is set in the DSP after the control amount is determined. When the state determined to be silent continues twice, the rewriting of the control parameter to the DSP for the audio signal determined from noise is postponed, and when the silent state is released in the subsequent cycles, the noise amount according to the noise amount at that time is canceled. It operates to set a new control amount determined by the DSP. By doing so, it is possible to solve the problem that occurs when the sound quality correction rate is changed according to the level of the audio reproduction signal.

[0057]

According to the present invention, when the level of the audio output signal is large, the volume and dynamic range expansion and the bass correction are suppressed and excessive correction is not performed. Does not cause discomfort in hearing.

Further, since the traveling noise adaptive correction is performed at the output level of the audio output signal whose audibility is corrected, the correction of the volume and the dynamic range and the boost correction of the low range are performed in accordance with the audible volume sensitivity characteristic. Discomfort in hearing is less likely to occur.

Further, the change of the sound quality correction rate at the time of sudden deceleration is made slightly slower than the change of the vehicle speed and further made slower at the time of sudden acceleration, so that the sound quality correction rate suddenly changes at the time of sudden acceleration, resulting in an uncomfortable feeling. Is less likely to occur.

Further, since the correction state immediately before that is maintained during the silence period when the audio output signal is silent or close to it, only noise is not increased, and at the time of transition from silence to voice. It is possible to prevent the volume from becoming excessively high temporarily.

[Brief description of drawings]

FIG. 1 is a block circuit diagram of a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration example of a level detection circuit according to the first exemplary embodiment.

FIG. 3 is an input / output characteristic diagram of the level detection circuit of FIG.

FIG. 4 is a sound quality control characteristic diagram of the first embodiment.

FIG. 5 is a characteristic diagram of the volume level control (amplitude amplification factor) of the first embodiment.

FIG. 6 is a diagram showing an example of a digital signal processing flow of volume level control according to the first embodiment.

FIG. 7 is a bass boost control characteristic diagram of the first embodiment.

FIG. 8 is a diagram showing an example of a digital signal processing flow of bass boost control according to the first embodiment.

FIG. 9 is a diagram showing a waveform compression control characteristic of the first embodiment.

FIG. 10 is a diagram showing an example of a flow of digital signal processing of waveform compression control according to the first embodiment.

FIG. 11 is a flowchart of the first embodiment.

FIG. 12 is a block circuit diagram of a second embodiment of the present invention.

FIG. 13 is a characteristic diagram of the auditory sense correction filter according to the second embodiment.

FIG. 14 is a diagram showing a configuration example of an auditory sense correction filter according to a second embodiment.

FIG. 15 is a block circuit diagram of Embodiment 3 of the present invention.

FIG. 16 is a control characteristic diagram at the time of sudden acceleration according to the third embodiment.

FIG. 17 is a control characteristic diagram during rapid deceleration of the third embodiment.

FIG. 18 is a flowchart of Example 3.

FIG. 19 is a block circuit diagram of Embodiment 4 of the present invention.

FIG. 20 is a diagram illustrating a configuration example of a silence detection circuit according to a fourth embodiment.

FIG. 21 is a flowchart of Example 4.

FIG. 22 is a block circuit diagram of a conventional audio signal processing device of a noise adaptive control system.

FIG. 23 is a diagram showing a general sound volume sensitivity characteristic of a human.

[Explanation of symbols]

 3 Amplifier 4 Speaker 5 Vehicle Speed Signal Detection Circuit 8 Microphone 9 Microcomputer (Control Device) 10 A / D Converter 11 Digital Signal Processing Integrated Circuit (DSP) 12 D / A Converter 13 Audio Signal Processing and Reproduction System 14 Level Detection Circuit 15 Microphone amplifier 16 Band division filter 17 Audio signal control system 27 Listening correction filter 28 Vehicle speed change estimation circuit 29 Acceleration volume adjustment time constant memory 30 Deceleration volume adjustment time constant memory 31 Silence detection circuit

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[Procedure amendment]

[Submission date] July 6, 1993

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

Also, the volume level of the audio output signal
The audibility is corrected and the corrected volume level
To adjust the volume increase rate of the audio output signal.
It is the one.

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0017

[Correction method] Change

[Correction content]

Further, the volume level of the audio output signal is audibly corrected, and the bass range component of the audio output signal and the increase rate of the waveform compression rate are adjusted by the corrected volume level.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Kenichi Taura, Kenichi Taura, No. 1 Baba-Zou, Nagaokakyo City Electronic Product Development Laboratory, Mitsubishi Electric Co., Ltd. (72) Masahiro Tsujishita, No. 1, Keio Nagaoka-Kiba Ichiba, Mitsubishi Electric Co., Ltd. (72) Inventor Atsushi Ishikawa 2-33 Miwa, Mita-shi Mita Manufacturing Co., Ltd. (72) Inventor Yutaka Otani 2-33 Miwa, Mita-shi Mita Mitsubishi Electric Corporation Inside the production facility

Claims (8)

[Claims] 1. A volume level of an audio output signal of an audio device provided in a vehicle is controlled according to a running noise level of the vehicle, and the volume level of the audio output signal is detected. An audio signal processing method, characterized in that the increase rate of the volume of the audio output signal is reduced as the detected volume level increases. 2. A low-frequency range component of an audio output signal of an audio device provided in a vehicle is controlled according to a running noise level of the vehicle,
An audio signal processing method, characterized in that a volume level of an audio output signal is detected, and an increase rate of a bass component of the audio output signal is reduced as the detected volume level is increased. 3. A device for controlling the waveform compression rate of an audio output signal of an audio device provided in a vehicle according to the level of a running noise level of the vehicle,
An audio signal processing method, wherein a volume level of an audio output signal is detected, and an increase rate of a waveform compression rate of the audio output signal is reduced as the detected volume level is higher. 4. The audio signal according to claim 1, wherein the volume level of the audio output signal is audibly corrected, and the increase rate of the volume of the audio output signal is adjusted according to the corrected volume level. Processing method. 5. A volume level of an audio output signal is audibly corrected, and an increase rate of a bass range component of the audio output signal is adjusted according to the corrected volume level. Audio signal processing method. 6. A volume level of an audio output signal is audibly corrected, and an increase rate of a waveform compression rate of the audio output signal is adjusted according to the corrected volume level. Audio signal processing method. 7. A means for correcting the volume of an audio output signal of an audio device provided in a vehicle according to the vehicle speed,
Means for detecting sudden deceleration and sudden acceleration of the vehicle, means for changing the sound quality correction rate of the audio output signal slightly slower than the change in the vehicle speed when the vehicle rapidly decelerates, and means for adjusting so as to change even more slowly when the vehicle suddenly accelerates. An audio signal processing device characterized by being provided. 8. A means for correcting the volume of an audio output signal of an audio device provided in a vehicle so as to increase as the running noise level of the vehicle increases, and detects silence or a state close to the audio output signal. means,
From the time when the silence is detected or a state close to this is detected by the detecting means until the voiced state is detected, the correction state of the audio output signal by the correcting means is set immediately before the silence or a state close thereto is detected. An audio signal processing device comprising means for holding a state.