JP3396506B2 - Audio signal compression and decompression devices - 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 signal compressing device and an expanding device for a wireless communication device such as a cordless phone.

[0002]

2. Description of the Related Art When a voice signal is transmitted by a wireless communication device, its band is limited. For example, a cordless phone is limited to a band of 300 Hz to 3 KHz. Since an actual audio signal has a band of 300 Hz to 15 KHz, an audio signal in which a high frequency is cut is transmitted, so that the sound reproduced on the receiving side and the actual sound may feel strange. The current situation. However, even in such a wireless communication device, there is a strong demand for audio reproduction with high fidelity, that is, with so-called high fidelity.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide an audio signal compression apparatus capable of compressing an actual audio signal frequency within a transmittable band, and to set the compressed audio signal frequency to an actual frequency. An object is to provide a decompressor for an audio signal to be returned.

[0004]

An audio signal compression apparatus according to the present invention compares the frequencies of an audio signal, which is an input signal, with a reference signal, and outputs an output corresponding to the difference between the comparison circuit and the output of the comparison circuit. A compression ratio adjusting circuit that compresses according to the set compression ratio, a voltage controlled oscillator whose output frequency changes according to the output of the compression ratio adjusting circuit, and an amplitude that changes according to the amplitude of the audio signal. It has an amplitude adjusting circuit for obtaining an output of the same frequency as the output frequency from the output of the voltage controlled oscillator, and the output of the amplitude adjusting circuit is used as an output signal. By replacing the compression ratio adjusting circuit with the expansion ratio adjusting circuit, the compression device becomes an audio signal expansion device.

[0005]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An audio signal compression apparatus according to an embodiment of the present invention will be described below with reference to the block diagram of FIG.
In FIG. 1, 1 is an input terminal, 2 is an output terminal, 3 is a frequency comparison circuit, 4 is a compression ratio adjusting circuit, 5 is a voltage controlled oscillator (VCO), 6 is an amplitude adjusting circuit, 7 is a reference frequency oscillator, and 8 is It is an amplitude comparison circuit. The compression ratio adjusting circuit 4
May be composed of a linear amplifier. A voice signal from a microphone is added as an input signal to the input terminal 1, and the voice signal is applied to the reference frequency oscillator 7 by the frequency comparison circuit 3.
From the frequency of the reference signal from. The frequency comparison circuit 3 produces an output corresponding to the frequency difference between the audio signal and the reference signal, and this output is applied to the compression rate adjustment circuit 4.

Then, the compression rate adjusting circuit 4 compresses the output of the frequency comparing circuit 3 at a set rate. An example of the equation showing the compression ratio is shown in the equation (1). (F _INA −f _RE ) / 4 (1) where f _INA is the frequency of the audio signal and f _RE is the frequency of the reference signal of the reference frequency oscillator 7. (F _INA −f _RE ) is a value of 0 or more, and when it is negative, the compression operation is not performed.
Therefore, the compression operation is performed for the frequency f _INA of the audio signal exceeding the reference frequency f _RE, and the output of the frequency comparison circuit 3 is compressed to 1/4 by the compression rate adjustment circuit 4. The output of the compression ratio adjusting circuit 4 is applied as a voltage to the voltage controlled oscillator 5. Since the output of the reference frequency oscillator 7 is also added to the voltage controlled oscillator 5, the voltage controlled oscillator 5 produces the output of the frequency f _OUTA shown in the equation (2). f _OUTA = {(f _INA −f _RE ) / 4} + f _RE (2) That is, the frequency output corresponding to the output of the compression ratio adjusting circuit 4 and the frequency f _{RE of the} reference signal are added to produce an output. Therefore, the relationship between the frequency f _OUTA of the output of the voltage controlled oscillator 5 and the frequency f _INA of the audio signal is as shown in Table 1. However,
The frequency f _{RE of the} reference signal is 1 KHz.

[0007]

[Table 1]

The output of the voltage controlled oscillator 5 is the amplitude adjusting circuit 6
In addition, the amplitude adjusting circuit 6 is controlled by the output of the amplitude comparing circuit 8. The amplitude comparison circuit 8 compares the audio signal from the input terminal 1 with the output of the amplitude adjustment circuit 6 to generate an output corresponding to the difference, and the amplitude adjustment circuit 6
The output amplitude of is controlled so as to change according to the audio signal. Therefore, the output of the amplitude adjusting circuit 6 has the same frequency as the frequency f _OUTA of the output of the voltage controlled oscillator 5, and the amplitude becomes the same as the audio signal from the input terminal 1. The output of the amplitude adjusting circuit 6 is used as the output signal of the compression device and is applied to the modulation circuit of the transmitter.

FIG. 3 is a diagram showing the relationship between the frequencies of the input signal and the output signal in FIG. 1. The horizontal axis of the coordinate axis is the frequency f _{INA of the} input signal, the vertical axis is the frequency of the output signal, and the voltage-controlled oscillator 5 is used. The frequency f _OUTA of the output of FIG. The solid line shows how the input signal f _INA is compressed at a rate of ¼ at frequencies above the reference frequency f _RE . In addition,
A dotted line is shown for comparison when the input signal is not compressed, that is, when the input signal and the output signal are the same. It can be seen from Table 1 that this compression device compresses the higher frequency f _INA far from the frequency f _{RE of the} reference signal, and can transmit the frequency of the audio signal in the vicinity of 10 KHz close to the transmission band. A low-pass filter may be connected to the input side of the voltage controlled oscillator 5 to eliminate noise and ripple caused by compression.

FIG. 2 shows a block diagram of a decompression device of the present invention, and the same parts as those in FIG. 1 are designated by the same reference numerals. The difference from FIG. 1 is that the expansion rate adjusting circuit 9 is used instead of the compression rate adjusting circuit 4, and the frequency of the audio signal can be expanded by this circuit 9. Normally, the compression device of FIG. 1 and the decompression device of FIG. 2 are used as a pair.
The decompressor is used on the receiver side. The compressed audio signal from the detection circuit is input to the input terminal 1, and the output terminal 2
A circuit for reproducing sound such as a speaker is connected to the.

Therefore, if the frequency f _RE is made the same and the expansion rate is set so as to expand by the compression rate set by the compression rate adjusting circuit 4, the frequency band of the audio signal input from the microphone in FIG. 1 can be reproduced. The expansion ratio corresponding to the equation (1) is set as in the equation (3). 4 (f _INB −f _RE ) (3) where f _INB is the frequency of the audio signal applied to the frequency comparison circuit 4 from the input terminal 1 in FIG. (F _INB
-F _RE ) is a value of 0 or more, and if it is negative, the expansion operation is not performed. The frequency f of the output of the voltage controlled oscillator 5 of FIG.
_OUTB is expressed by equation (4). f _OUTB = 4 (f _INB −f _RE ) + f _RE (4) Therefore, the relationship between the frequency f _OUTB of the output of the voltage controlled oscillator 5 and the frequency f _INB of the audio signal in the expansion device of FIG.
It becomes like Table 2. However, the frequency f _{RE of the} reference signal is shown in FIG.
It is 1 KHz, which is the same as the compression device of.

[0012]

[Table 2]

When a compression device and a decompression device are used in a pair, f _outA = f _INB and f _INA = f _OUTB , so that the voice signal input to the compression device on the transmission side is accurately _detected by the decompression device on the reception side. However, it is clear from Tables 1 and 2 that such a relationship is established. FIG. 4 is a diagram showing the relationship between the frequencies of the input signal and the output signal of FIG. 2, where the horizontal axis of the coordinate axis is the frequency f _{INB of the} input signal and the vertical axis is the frequency of the output signal, which is the frequency of the output of the voltage controlled oscillator 5. f _OUTB
Is represented. The solid line shows that the input signal f _INB is expanded four times at a frequency exceeding the frequency f _RE . The dotted line is shown for comparison when the input signal is not expanded, that is, when the input signal and the output signal are the same.

Therefore, by using the transmission device and the decompression device of the present invention to compress and transmit a voice signal to 1/4, and reproduce it, almost all the band of the voice signal is transmitted, and the high fidelity of the voice signal is obtained. Playback is possible. The compression rate of the transmission device of the present invention and the expansion rate of the decompression device can be set freely, and may be adjusted according to practical use. Further, the setting of the frequency of the output of the voltage controlled oscillator 5 need not be limited to the expressions (2) and (4). For example, the frequency f _{RE of the} reference signal is (−f _RE ), (× f _RE ) instead of (+ f _RE ).
_RE ) may be present in the formula.

[0015]

As described above, by using the audio signal compressing device and the expanding device of the present invention, almost all the audio signal band is transmitted even in a wireless communication device having a limited transmission band. It is possible to play. Therefore,
High-fidelity audio signals can be reproduced and meet market demands. Further, the band of the audio signal being transmitted is compressed differently from the band of the input audio signal, and the compression ratio can be different depending on the frequency. This is a very convenient advantage for maintaining confidentiality.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of an audio signal compression apparatus of the present invention.

FIG. 2 is a block diagram showing an embodiment of an audio signal expansion device of the present invention.

FIG. 3 is a diagram showing a relationship between frequencies of an input signal and an output signal of FIG.

FIG. 4 is a diagram showing a relationship between frequencies of an input signal and an output signal of FIG.

[Explanation of symbols]

1 input terminal 2 output terminals 4 Compression rate adjustment circuit 9 Expansion rate adjustment circuit

Claims (2)

(57) [Claims] 1. A comparison circuit for comparing frequencies of an audio signal which is an input signal and a reference signal and obtaining an output according to the difference, and a compression ratio adjusting circuit for compressing the output of the comparison circuit according to a set compression ratio. , A voltage-controlled oscillator whose output frequency changes according to the output of the compression ratio adjusting circuit, and an amplitude whose amplitude changes according to the amplitude of the audio signal, and which has the same frequency as the output frequency of the voltage-controlled oscillator. An audio signal compression device having an amplitude adjusting circuit obtained from an output, wherein the output of the amplitude adjusting circuit is used as an output signal. 2. A comparison circuit for comparing the frequencies of an audio signal which is an input signal and a reference signal and obtaining an output according to the difference, and an expansion rate adjusting circuit for expanding the output of the comparison circuit according to a set expansion rate. , A voltage-controlled oscillator whose output frequency changes according to the output of the expansion rate adjusting circuit, an amplitude which changes according to the amplitude of the audio signal, and which has the same frequency as the output frequency of the voltage-controlled oscillator. An audio signal decompressing device having an amplitude adjusting circuit obtained from an output, wherein the output of the amplitude adjusting circuit is used as an output signal.