JPH07202819A - Audio signal compression/expansion device - Google Patents

Abstract

PURPOSE:To eliminate a sense of incongruity of a reproduced sound by adding a signal at a proper level whose partial frequency band is eliminated to a signal subject to compression/expansion processing. CONSTITUTION:An input signal is given to a BPF 4, in which a setting band component signal not requiring compression/expansion processing is extracted and the signal is fed to a subtractor 5. The subtractor 5 subtracts the signal extracted by the BPF 4 from the input signal and a signal from which a setting band component is eliminated is fed to a voltage controlled amplifier 1. An output voltage level of a level detector 2 is received by a controller 3, a gain of the amplifier 1 is adjusted by a control voltage of the controller 3, and an output of the amplifier 1 is fed to an adder 6. A multiplier 7 multiplies a prescribed coefficient with the setting band component signal extracted by the BPF 4. The adder 6 adds an output signal of the multiplier 7 to the signal resulting from eliminating the setting band component and subject to level adjustment and the sum signal is transmitted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to audio signal compression /
The present invention relates to a decompression device, and more particularly to an audio signal compression / decompression device that performs compression or decompression processing that does not cause discomfort in reproduced sound.

[0002]

2. Description of the Related Art For example, in an on-vehicle audio system, running noise generated by running a vehicle masks a low level reproduced sound by hearing, so that the reproduced sound level is raised or lowered to raise the hearing level. Audio signal compression / decompression devices that perform dynamic range compression and decompression such as the above have been put into practical use.

FIG. 4 shows a basic block diagram of a conventional audio signal compression / decompression device. In FIG. 4, the input signal is directly input to the voltage controlled amplifier 1, and its output is input to the level detector 2 to detect the average voltage level. The gain adjustment in the voltage controlled amplifier 1 is
This is performed based on the input / output characteristics set by the compression process or the expansion process set by the user. FIG. 5 shows the normal characteristic and the extension characteristic of this input / output characteristic example.
The controller 3 obtains the gain according to the input / output characteristics based on the voltage level from the level detector 2 and outputs the gain according to the voltage control amplifier 1
Set to.

[0004]

As described above, the compression or expansion processing of the dynamic range in the conventional audio signal compression / expansion device is applied to the entire frequency band of the input signal. Therefore, processing may be performed on a signal in a band that is not desired to be processed, and reproduced sound may be uncomfortable. For example, when a decompression process is performed on a vocal sound such as a human voice, there is a problem that the processed vocal sound is swayed like a breath sound, resulting in an unnatural sound.

SUMMARY OF THE INVENTION An object of the present invention is to provide an audio signal compression / expansion device capable of performing compression or expansion processing which does not cause a feeling of strangeness in reproduced sound.

[0006]

In order to solve the above-mentioned problems, an audio signal compression / expansion device of the present invention includes a filter for extracting a predetermined band signal from an input signal, and a filter for extracting the predetermined band signal from the input signal. A subtractor for subtracting and outputting the predetermined band signal, a level variator for amplifying or attenuating the output of the subtractor with variable gain, and a level detector for detecting an output level or an input level of the level variator, A controller that controls the gain of the level variable device according to the level detected by the level detector; and an adder that adds the output component of the filter to the output of the level variable device and outputs the result. Composed.

[0007]

In the present invention, the signal from which the frequency band unnecessary for the compression / expansion effect is removed is subjected to the compression / expansion process, and the removed frequency band is added to the signal compressed / expanded at an appropriate level to obtain a natural effect. Get the effect.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a configuration block diagram showing an embodiment of an audio signal compression / decompression device according to the present invention. In FIG. 1, the components designated by the same reference numerals as those in FIG. 4 indicate components having the same function. From the input signal, a bandpass filter 4 extracts a set band component signal that does not require compression or decompression processing and supplies the signal to a subtractor 5.
The subtractor 5 subtracts the extracted signal from the bandpass filter 4 from the input signal, and sends the signal from which the set band component has been removed to the voltage controlled amplifier 1.

The output of the voltage controlled amplifier 1 whose gain is adjusted by the control voltage from the controller 3 which receives the output voltage level from the level detector 2 is supplied to the adder 6. The multiplier 7 multiplies the set band component signal extracted by the band pass filter 4 by a predetermined coefficient. The adder 6 adds the output signal of the multiplier 7 to the level-adjusted signal from which the set band component has been removed, and outputs the added signal.

FIG. 2 shows the L channel (c
FIG. 7 is a block diagram of a configuration in which the present embodiment is applied to an h) signal and an R channel (ch) signal. The bandpass filter 4 extracts the vocal band component from the Lch signal and the Rch signal supplied from the terminals Lin and Rin, and the subtracter 5
L and 5R, and multipliers 7L and 7R. Subtractor 5
In L and 5R, L with the vocal band signal removed respectively
The ch and Rch signals are output to the voltage controlled amplifiers 1L and 1R. Amplifiers 1L and 1 detected by the level detector 2
The level of the signal obtained by adding the output of R by the adder 8 is supplied to the controller 3, and the control voltage from the controller 3 controls the gains (coefficients) of the voltage controlled amplifiers 1L and 1R. The outputs of the amplifiers 1L and 1R are extracted by the bandpass filter 4 by the adders 6L and 6R, and added by the signals multiplied by the predetermined coefficient by the multipliers 7L and 7R, and the added signals are Lch and Rch.
Is output as the output signal of.

In this embodiment, the voltage controlled amplifier 1L
The output including the vocal range is obtained by expanding the sound with the gains of 1R and 1R and returning the vocal sound with the multipliers 7L and 7R, but the output level of the amplifiers 1L and 1R is lower than the normal level. I will end up. At this time, if the coefficients of the multipliers 7L and 7R are set to 1.0, the expanded sound that has fallen below the normal level has a lower level than the sound in the vocal band, and the stereo feeling is impaired.

Therefore, in this embodiment, when the expansion processing is not performed, the coefficient of 7R of the multiplier 7L is set to 1.0, and when the expansion processing is applied, the coefficient is reduced according to the degree of expansion. Change to a value.

FIG. 3 shows still another embodiment of the present invention,
In addition to the components of the embodiment shown in FIG. 1, by providing the low pass filter 9 in the preceding stage of the band pass filter 4,
The filter accuracy is improved.

In the above embodiments, the voltage control amplifier may not only amplify the input signal but also attenuate it.
Further, although the level detector 2 detects the output level of the voltage controlled amplifier 1, it may detect the input level of the voltage controlled amplifier, or may detect the input level of the input signal or the output signal level. You can

[0015]

As described above, according to the present invention,
It is possible to prevent the reproduced sound from feeling uncomfortable even if the compression or expansion processing is performed, for example, to prevent the sound fluctuation phenomenon due to the expansion processing of the vocal sound.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment of an audio signal compression / decompression device according to the present invention.

FIG. 2 is an L channel (ch) signal and R of a stereo signal
It is a block diagram of a configuration in which this embodiment is applied to a channel signal.

FIG. 3 is a configuration block diagram showing another embodiment of the present invention.

FIG. 4 is a configuration block diagram of a conventional audio signal compression / decompression device.

5 is a diagram showing an input / output characteristic example of the audio signal compression / decompression device shown in FIG.

[Explanation of symbols]

 1,1L, 1R Voltage control amplifier 2 Level detector 3 Controller 4 Bandpass filter 5,5L, 5R Subtractor 6,6L, 6R Adder 7,7L, 7R Multiplier 8 Adder 9 Lowpass filter

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[Procedure amendment]

[Submission date] June 23, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 4]

[Figure 5]

[Figure 3]

Claims (1)

[Claims] 1. A filter for extracting a predetermined band signal from an input signal, a subtractor for subtracting and outputting the predetermined band signal extracted by the filter from the input signal, and an output of the subtractor with a variable gain. A level variator that amplifies or attenuates, a level detector that detects an output level or an input level of the level variator, and a controller that controls the gain of the level variator according to the level detected by the level detector And an adder which adds the output component of the filter to the output of the level variable device and outputs the added component.