JP3284176B2 - Audio equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an audio apparatus capable of listening to audio sound equivalent to a quiet environment even when used in a vehicle or the like where the external noise level (noise) changes greatly, for example.

[0002]

2. Description of the Related Art In a compact disk (CD) player for a vehicle or the like, or an audio device used outdoors, a listening environment changes greatly depending on a surrounding noise state, and it is difficult to always output good sound. For example, when music of a CD is reproduced in a running car, or in the case of a quiet tune, the noise caused by the running of the car (hereinafter, not caused by the audio device) even at a normal reproduction volume level. An external noise or the like is referred to as external noise).

FIG. 6 shows the measurement of loudness (loudness) of a pure tone under noise.

FIG. 6 is a loudness curve accompanying a change in the level of 1000 Hz when white noise of various levels is added to a pure tone of 1000 Hz. The horizontal axis is the actual sound pressure level (physical quantity, unit dB), and the vertical axis is the vertical axis. It shows the loudness of the sound (the loudness of the sound (amount of sensation), unit thorn). The unit of loudness for human perception is 1
The volume of a pure tone of 000 Hz and 40 dB is one thorn.

[0005] In FIG. 6, the noise level is set to 50 dB, 60 dB, 70 dB when there is no noise (only pure tone) and there is noise.
dB, 80dB, 90dB, 100dB,
It can be seen from the figure that the higher the noise level, the harder it is to hear a pure tone. That is, from FIG. 6, the loudness is
It can be seen that it decreases sharply as it approaches the minimum audible limit, and the degree depends on the noise level. This indicates a masking effect due to white noise.

Therefore, as described in, for example, Japanese Patent Application Laid-Open No. 7-235850, an audio apparatus has been proposed which can obtain a dynamic range compressed audio output signal when the external noise level is high. ing. In this method, when the frequency characteristic of external noise is flat (white), for example, when the noise level is high, the signal level of the small level becomes high, and good audio reproduction can be performed according to the noise level.

[0007]

FIG. 7 shows that a narrow band noise of 70 dBSPL centered at 1000 Hz is 500 to 2 dB.
The vertical axis indicates the amount of partial masking that affects the loudness of the pure tone in the range of 500 Hz, ie, the amount of partial masking, that is, the two tones when the pure tone without the masking tone and the masked pure tone sound equally loud. Shows the level difference. The parameter indicates the level of the loudness of the masked pure tone.

As is apparent from FIG. 7, for example, a pure tone of 1000 Hz that can be heard with 5 horns without masking has a higher sound pressure level of 62 dB than a pure tone that can be heard with a magnitude of 5 horns without masking. I have. Conversely, it indicates that in order to hear a sound that sounds as large as 5 horns without noise and at the same level with masking, it is necessary to increase the volume by 62 dB. And in the figure, for example, 1000H
It also shows that the pure tone audible at 5 horns at z receives 62 dB of masking, but only 2000 dB at 16 Hz. As described above, it is known that the range of frequencies that can be masked is limited in the case of narrow-band noise.

From this fact, when the frequency characteristic of the external noise is not flat, the masking amount changes for each band. Therefore, if the dynamic range is changed at once regardless of the band, the loudness differs from the original sound depending on the band, and as a result, the loudness does not change. There was a problem with natural sound quality. That is, when noise is concentrated in the low frequency range, the loudness of the audio signal in the high frequency range is increased. Conversely, when noise is concentrated in the high frequency range, the loudness of the audio signal in the low frequency range is increased. In conventional audio devices, it was possible to solve this problem by using a glico.However, since the user had to manually operate the device, it was difficult to make optimal settings for ever-changing external noise. It was very difficult.

[0010] From the above, it is an object of the present invention to automatically perform sound control according to the noise level for each band and compensate for loudness, so that music can be enjoyed under noise even as in a quiet state. It is to provide an audio device.

[0011]

SUMMARY OF THE INVENTION An audio apparatus according to the present invention comprises a means for inputting a signal from an audio source and outputting sound.
Band and the level of the input signal from the audio source.
Means to calculate each time, and to detect external noise and
Noise level calculating means for calculating the noise level for each band,
Outside based on the noise level calculated by the level calculation means.
Increase in minimum audible limit from silence for each band due to local noise
Means for calculating the amount of audio, and audio software for each calculated band.
Source and noise level calculation means.
To the minimum audible rise calculated based on the
Volume adjusting means for adjusting the sound output for each band in accordance with
And the volume adjustment means includes the calculated minimum audible value.
The amount of increase in the input signal from the audio source
Higher levels compress the dynamic range
Based on the volume rise amount conversion table formed
The volume level is adjusted for each region .

Here, when the minimum audibility limit for each band due to external noise is calculated, and the sound output is adjusted for each band based on the amount of increase in the minimum audibility limit from silence, it is more preferable that the sound quality does not deteriorate. Also, for example, if the minimum audibility increase due to noise is large and the level of the input signal from the audio source is large, if the dynamic range is formed so as to be compressed, it is similar to a quieter state even under noise. An audio device that can enjoy music can be provided. Further, the calculation of the level of the input signal is performed by calculating a level for each of the divided bands when the audio source is divided into bands in advance, or
When the audio source is divided into bands in advance, the volume adjusting unit can provide an audio device that achieves high quality by reducing the processing amount by adjusting the volume for each of the divided bands.

[0013]

FIG. 1 shows an embodiment of the present invention.

In FIG. 1, reference numeral 10 denotes an audio source such as a CD reproducing device, an MD reproducing device, a tape reproducing device, and a radio tuner. Reference numeral 11 denotes an A / D conversion unit, which converts an analog signal output from the audio source 10 into a digital signal by an A / D conversion circuit 11 and calculates an average signal level through a BPF circuit 12 that performs band division. The signal is output to the signal level calculator 13 and the volume controller 14. If the audio source 10 is a CD playback device or an MD playback device, and its output signal has already been D / A converted to an analog signal, it is input to the BPF circuit 12 via the A / D conversion circuit 11. However, when the digital signal is output as it is, the A / D conversion circuit 11 is passed. The volume control unit 14 controls the level of the band-divided signal based on the output of a volume adjustment unit 23 described later. The synthesizing unit 15 is a filter for synthesizing the band-divided signal. The signal is converted into an analog signal by the D / A conversion circuit 16, amplified by the power amplifier 17, and subjected to electroacoustic conversion by the speaker 18.

Reference numeral 19 denotes a noise detection circuit which constantly detects the level of external noise. The detected noise is converted into a digital signal by an A / D conversion circuit 20, and the BPF circuit 2
After the band division by 1, the average noise level calculator 22 calculates an average noise level for each band. Volume adjuster 23
Sets the audio signal volume for each band based on the set value of the volume adjuster 24 that can be set by the user and the calculated average signal level and average noise level, and outputs the audio signal to the volume control unit 14.

The entire processing is controlled by the CPU 25.

Note that the average noise level calculating section 22 simultaneously grasps the output voice level and detects a value obtained by subtracting the output voice level from the detected surrounding voice level as the noise level. I do. In the case of a headphone-type player, the speaker 18 is replaced with a headphone, but since the output sound does not overlap with external noise, the above-described subtraction processing is not necessary.

As described above, the audio device is provided with the volume control unit 23 for each band, and is configured to automatically control the volume according to the noise level for each band. Can automatically change the volume of the output signal so that the sound is always obtained in the best listening state. In other words, depending on the type of noise, there are bands where the audio signal is easy to hear and bands where it is hard to hear, resulting in unnatural audio playback. , The listening state can be improved.

In order to always obtain the best listening state, the sound volume for each band may be changed stepwise according to the frequency characteristics of the external noise level. The operation of the volume adjustment unit 23 will be described in more detail with reference to the flowchart of FIG.

Step S1: Set value v of volume controller 24
(0 ≦ v ≦ 1) and an external noise level Nn for each band
And inputs the signal level Sn. Note that n is a band number.

Step S2: The noise level Nmin of the band with the lowest noise level is calculated.

Step S3: A normalized noise level Nn is calculated from the noise level of each band by the following equation.

Nn = (Nn-Nmin) * v Step S4: A volume increase Xn for each band is calculated from Nn and Sn using the conversion table shown in Table 1.

[0024]

[Table 1]

Step S5: Xn is output to the volume controller 14.

With the above processing, the sound volume for each band is set.
For example, according to Table 1, the noise level in a certain band is 20
When the signal level is 30 dB and the signal level is 30 dB, the signal level is set to 1
It will increase by 5 dB. In addition, Table 1 considers that the loudness rapidly decreases as approaching the minimum audible limit as described above, and as a result, a loudness that is the same as that in a quiet time even under noise can be obtained. That is, in Table 1, when the amount of increase from the minimum audible limit due to noise is large and the level of the input signal from the audio source 10 is large, the dynamic range is formed so as to be compressed, and the noise is more quiet under noise. The music can be enjoyed in the same way as the state.

Since the external noise level usually fluctuates finely, the signal divided by the BPF 20 is appropriately filtered to obtain the average noise level at a certain point in time, and the volume is adjusted. It is desirable to supply it to the unit 23.

FIG. 3 shows a second embodiment for estimating the minimum audibility increase due to external noise and setting the volume in order to further improve the quality.

This is different from FIG. 1 in that the BPF 20 and the average noise level calculator 22 are replaced by a minimum audibility calculator 26.
Is different. An example of a minimum audibility calculation procedure performed by the minimum audibility calculation unit 26 will be described with reference to the flowchart of FIG.

Step S11: A / D converted noise is input. Step S12: FFT analysis is performed at 512 points. X (i) is a spectrum line, and i represents a spectrum line number.

Step S13: Calculate the sound pressure of each band (F
FT output maximum value).

Step S14: All the spectral lines are added in each critical band to obtain Xn (z) (j). Note that z (j) represents the bark value of the j-th critical band.

Step S15: The masking threshold in each critical band is obtained by the following equation.

[0034]

(Equation 1)

Step S16: Total masking amount LTg
(I) is obtained by the following equation.

[0036]

(Equation 2)

Here, m represents the number of critical bands.

Step S17: LTg (i) for each band
Then, a value Nn obtained by subtracting the minimum audibility during silence in Table 2 from the maximum value (minimum audibility) of the above is output to the volume adjustment unit 23 as a noise level.

[0039]

[Table 2]

With the above processing, the minimum audible increase is calculated. However, this is a simplified version of the psychoacoustic analysis method used in audio encoding such as MPEG, but is not limited to this algorithm, and another algorithm may be used.

Although this embodiment requires a larger amount of calculation than the embodiment of FIG. 1, since the influence of masking is strictly taken into account, the deterioration of sound quality due to the influence of noise can be further suppressed.

In the embodiment shown in FIG. 3, a table as shown in Table 1 is employed. If the above-mentioned increase in the minimum audible limit due to noise is large and the level of the input signal from the audio source 10 is large, the dynamic range becomes large. If formed so as to be compressed, it is possible to provide an audio device that can enjoy music in the same manner as in a quiet state even under noise.

Next, the case where the audio signal is band division coded data such as MD or MPEG will be described. FIG.
3 relates to an improvement of the embodiment of FIG. 3. In this case, as shown in FIG. 5, the BPF 12 shown in FIG. 3 is unnecessary, and the average signal level calculating unit 13 and / or the volume adjusting unit 23 By calculating the average signal level and / or adjusting the volume of the band-divided signal for each band, the amount of calculation can be reduced as compared with FIG. It is clear that the embodiment shown in FIG. 1 can be similarly configured without the need for the BPF 12.

[0044]

As described above, the audio apparatus of the present invention automatically controls the volume according to the noise level for each band, and compensates for the loudness so that the music can be reproduced in the same manner as in the quiet state even under noise. You can enjoy. In other words, since the volume is automatically increased mainly in the band that is easily masked by noise as compared to the one that simply increases the overall volume level during noise, the best audio playback is always possible even if the type of noise changes Therefore, it is effective for in-vehicle audio and portable headphones.

[Brief description of the drawings]

FIG. 1 is a block diagram of an audio device showing one embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation of a volume adjustment unit.

FIG. 3 is a block diagram of an audio device showing another embodiment of the present invention.

FIG. 4 is a flowchart illustrating a procedure for calculating a minimum audibility limit.

FIG. 5 is a block diagram of an audio device according to still another embodiment of the present invention.

FIG. 6 is an explanatory diagram of a loudness curve affected by white noise.

FIG. 7 is an explanatory diagram of masking of a pure tone by narrow-band noise.

[Explanation of symbols]

 Reference Signs List 10 audio source 11 BPF 13 average signal level calculation unit 14 volume control unit 18 speaker 19 noise detection circuit 21 BPF 22 average noise level calculation unit 23 volume control unit 25 CPU 26 minimum audible limit calculation unit

Continuation of front page (56) References JP-A-5-175772 (JP, A) JP-A-5-37270 (JP, A) JP-A-61-90508 (JP, A) JP-A-5-299957 (JP) JP-A-7-307632 (JP, A) JP-A-7-7350 (JP, A) JP-A-7-235850 (JP, A) JP-A-7-66651 (JP, A) 60-35624 (JP, U) (58) Fields studied (Int. Cl. ⁷ , DB name) H03G 3/32 G10K 15/04 304 G10L 21/02

Claims (4)

(57) [Claims] 1. A means for inputting a signal from an audio source and outputting a sound, a means for calculating a level of an input signal from the audio source for each band, and a noise for detecting external noise and calculating a noise level for each band. Level calculating means and a noise level calculated by the noise level calculating means.
Means for calculating the minimum audible increase from the quiet time for each band due to external noise, and the calculated audio source level and noise for each band.
Based on the noise level calculated by the noise level calculation means.
Depending on the amount of increase of the calculated minimum audible, and a volume adjustment means for adjusting for each band the sound output, the sound volume adjusting means, a lot amount of increase in minimum audible calculated, audio source higher the level of the input signal from the large based on the formed volume increased amount conversion table as dynamic range is compressed, the volume record for each band
An audio device characterized by adjusting a bell . 2. When the input signal from the audio source is band division coded data, the sound volume adjustment means includes:
2. The audio device according to claim 1, wherein the sound volume is adjusted for each band with respect to the signal that has been subjected to band division in advance. 3. The apparatus according to claim 1, wherein the means for calculating the level of the input signal for each band calculates a level corresponding to each of the divided bands of an audio source that has been divided into bands in advance. The audio device according to claim 2. 4. The sound volume adjusting means for adjusting the sound output for each band adjusts the sound output corresponding to each divided band of the audio source divided in advance. Alternatively, the audio device according to claim 2.