JPH06276163A - Digital audio transmitting device and receiving device - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To provide a digital audio transmitter and a receiver having a small number of circuits, which are compatible with encoding systems of different sampling frequencies. [Structure] The transmission signal is a digital low-pass filter 2
A band conversion unit 2 including 4 and 1/2 thinning circuits 25,
It is supplied to the high quality speech encoder 27. Band conversion unit 2
Output signal is provided to a telephone quality speech encoder 26. The output signals of the telephone quality speech encoder 26 and the high quality speech encoder 27 are supplied to the selector 28. The received signal is also supplied to the telephone quality speech decoder 32 and the high quality speech decoder 36. The output signal of the telephone quality voice decoder 32 is a sampling frequency conversion unit 10 including a double interpolation circuit, a digital low-pass filter 34, and an amplifier 35.
Is supplied to. Output signals of the sampling frequency conversion unit 10 and the high-quality speech decoder 36 are supplied to the selector 37.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital audio transmitting apparatus and a receiving apparatus corresponding to a plurality of encoding systems having different reproduction frequency bands in, for example, digital audio communication, and particularly to a reproducing frequency depending on the compression encoding system. Even if there are differences in band and sampling frequency,
The present invention relates to a digital audio transmitting device and a receiving device for directly using an A / D converter, a D / A converter, or the like that uses a single sampling frequency by converting the sampling frequency.

[0002]

2. Description of the Related Art Telephone voice quality and high-quality voice quality are known as voice quality of a voice encoding system used for transmitting a digital audio signal. Different sampling frequencies are used for telephone voice quality and high quality voice quality. Therefore, it is necessary to change the signal transmission rate according to the difference in the encoding method. In particular, when performing asymmetrical communication with different qualities between transmission and reception, for example, telephone quality is used as the transmission voice and high-quality voice quality is used as the reception voice, the A / D conversion unit and the D / A conversion are performed. Separate devices must be used to vary the sampling frequency between sections. However, increasing the number of devices leads to higher costs, resulting in a single A / D
There is a demand for a method capable of performing asymmetric communication and the like in the conversion unit and the D / A conversion unit.

As a conventional digital audio transmitter and receiver, the one shown in FIG. 5 is known. In FIG. 5, the transmitter comprises 50 to 59, and the receiver comprises 5.
5, 60-68. That is, the transmitting unit includes the input terminal 50, the low-pass filter 51A, and the low-pass filter 5
1B, A / D converter 52 for telephone voice, A / for high-quality voice
D converter 53, selector 54, echo canceller 55,
Telephone quality speech encoder 56, high quality speech encoder 5
7, a selector 58 and an output terminal 59. In addition, the receiving unit includes an input terminal 60, a telephone quality voice decoder 61,
High-quality voice decoder 62, selector 63, echo canceller 55, telephone quality voice D / A converter 64, high-quality voice D / A converter 65, low-pass filter 66A, low-pass filter 66B, selector 67 and output Terminal 68
Consists of.

A case of transmitting and receiving a digital audio signal using the digital audio transmitting apparatus and the receiving apparatus will be described below. At the time of transmission, the transmitted voice is input from the input terminal 50 as an analog signal. This analog signal is supplied to the low-pass filters 51A, 5A and 5A.
1B, to the A / D converter 52 (sampling frequency is, for example, 8 kHz) and the A / D converter 53 (sampling frequency, for example, 16 kHz) corresponding to the frequency band and the sampling frequency of the encoding method. To be done. A / D converter 5
The digital output signal 2 and the digital output signal of the A / D converter 53 are supplied to the selector 54. Selector 5
The digital signal selected by 4 is input to the echo canceller 55. At this time, the echo canceller 55
Then, receiving the encoding method information on the transmitting side, the transmission / reception speed of the input / output signal is changed in accordance with a predetermined encoding method.

The digital signal from the echo canceller 55 is supplied to a telephone quality speech coder 56 (sampling frequency is, for example, 8 kHz) and a high-quality speech speech coder 57 (sampling frequency is, for example, 16 kHz). In these encoders 56 and 57, the supplied signal is code-compressed, and a code corresponding to the digital signal is selected by a selector 58 according to a predetermined encoding method.
Output to. The selector 58 selects one of the code codes and transmits the code code via the output terminal 59 and a digital line (not shown).

Further, at the time of reception, the code code received through the digital line and the input terminal 60 is in accordance with each coding system, and the telephone quality speech decoder 6
1 (sampling frequency is 8 kHz, for example) and is supplied to the high-quality speech decoder 62 (sampling frequency is 16 kHz, for example). In the telephone quality speech decoder 61 and the high-quality speech decoder 62, the supplied code code is decoded and expanded, and the digital signal is supplied to the selector 63. The digital signal selected by the selector 63 is input to the echo canceller 55 and subjected to predetermined processing according to the encoding method information on the receiving side.

The digital output signal of the echo canceller 55 is a D / A converter 64 (with a sampling frequency of 8 kHz, for example).
z), D / A converter 65 (sampling frequency is, for example, 16 k
Hz), and D according to the encoding method, respectively.
/ A converted. The digital output signal of the D / A converter 64 is supplied to the low-pass filter 66A, and D / A
The digital output signal of the A converter 65 is supplied to the low pass filter 66B. Low pass filters 66A, 66
One of the B output signals is selected by the selector 67 and supplied to the input terminal 68. In this way, the receiving state is established.

[0008]

By the way, in the above-mentioned digital audio transmitter and receiver, an independent low-pass filter must be provided for each encoding system having a different reproduction frequency band. Further, when trying to perform asymmetric communication, since the sampling frequency is different between the transmitting side and the receiving side, independent A / D converters and D / A converters are required.

Further, when directly connected to another signal processing device such as an echo canceller, the transmission rate of the signal changes depending on the encoding system having different sampling frequencies. Therefore, it is necessary to convey the information of the encoding method to the echo canceller and the peripheral device. Especially for asymmetric communication,
Since it is necessary for the transmitting side and the receiving side to independently provide information on the encoding method, the addition of the interface at the input / output portion becomes very large.

Therefore, an object of the present invention is to provide a digital audio transmitting apparatus and a receiving apparatus which can reduce the circuit scale by unifying the sampling frequencies.

[0011]

According to the present invention, there is provided a band conversion section for reducing a band and a sampling frequency of a digital audio signal, a low sampling frequency coding section for a first voice quality, and a second sampling frequency coding section. Is a digital voice transmitting apparatus including a high sampling frequency coding unit for the voice quality, and a selector for selecting a code code from the low sampling frequency coding unit and the high sampling frequency coding unit.

The present invention also provides a low sampling frequency decoding unit for the first voice quality, a high sampling frequency decoding unit for the second voice quality, and a low sampling frequency decoding unit. Of the sampling frequency conversion unit for increasing the sampling frequency of the output signal, and a selector for selecting the digital signals from the low sampling frequency decoding unit and the high sampling frequency decoding unit.

[0013]

During transmission, the transmission signal output from the A / D converter or the echo canceller in the high sampling frequency format is supplied to the band conversion section or the high sampling frequency encoding section. The transmission signal input to the band conversion unit has its sampling frequency reduced, and is output as a code code from the low sampling frequency encoding unit. On the other hand, the transmission signal directly input to the high-sampling frequency encoding unit also outputs a code code. These code codes are supplied to the selector.
The selector selects a predetermined encoding method and outputs it as transmission data.

Further, at the time of reception, the code code is input to the low sampling frequency decoding unit or the high sampling frequency decoding unit, and is decoded and expanded by each coding method. The output signal of the low sampling frequency decoding unit is supplied to the sampling frequency conversion unit because its sampling frequency becomes equivalent to the high sampling frequency. The sampling frequency of the signal supplied to the sampling frequency conversion unit is equal to the high sampling frequency. The output signal of the sampling frequency converter is output to the selector. On the other hand, the signal output from the high sampling frequency decoding unit is directly output to the selector. In the selector, the signal decoded and expanded by the predetermined encoding method is selected and supplied to the echo canceller or the D / A converter.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the principle of a digital audio transmitter and receiver according to the present invention. Note that FIG. 1A is a block diagram showing the configuration of the transmitting side, and FIG. 1B is a block diagram showing the configuration of the receiving side. In FIG. 1A, the digital audio signal input from the input terminal 1 is supplied to the band conversion unit 2 and the high sampling frequency encoding unit 3. In addition,
In the band conversion unit 2, the input signal is subjected to band reduction and sampling frequency reduction. Further, as will be described later, the band conversion unit 2 includes a digital low pass filter and a thinning circuit. The output of the band conversion unit 2 is supplied to the low sampling frequency encoding unit 4.

The low sampling frequency encoding unit 4 has, for example, a sampling frequency of 8 kHz and a reproduction frequency upper limit of 3.4 kHz.
Is a telephone quality voice coding system. In addition, the high sampling frequency encoding unit 3 has, for example, a sampling frequency of 16k.
Hz, and the reproduction frequency upper limit is 7.0 kHz. In any encoding method, if the sampling frequency is a sampling frequency of an A / D conversion unit and a D / A conversion unit, which will be described later, or a divisor of the operating frequency of the echo canceller. The coding method and its sampling frequency are not limited.

The signals code-compressed in the high sampling frequency encoding unit 3 and the low sampling frequency encoding unit 4 are supplied to the selector 5, respectively. Either one of the signals is selected by the selector 5 and is output as a code through the output terminal 6.

In FIG. 1B, the code code input from the input terminal 7 is supplied to the low sampling frequency decoding unit 8 and the high sampling frequency decoding unit 9 to be decoded. The output of the low sampling frequency decoding unit 8 is supplied to the sampling frequency conversion unit 10. As will be described later, the sampling frequency conversion unit 10 includes a double interpolation circuit, a digital low pass filter, and an amplifier. The sampling frequency converter 10 increases the sampling frequency of the supplied signal. The respective outputs of the high sampling frequency decoding unit 9 and the sampling frequency converting unit 10 are supplied to the selector 11, and one of them is selected. The selected signal is output from the output terminal 12 as an audio signal.

FIG. 2 is a detailed circuit block diagram of the digital audio transmitter and receiver according to the present invention. In FIG. 2, the transmitting unit includes 21 to 29, and the receiving unit includes 31 to 39. That is, the transmission unit includes the input terminal 21, the A / D converter 22, the echo canceller 23, the band conversion unit 2, the telephone quality speech encoder 26, the high-quality speech encoder 27, the selector 28, and the signal multiplexer 29. Consists of. Further, the receiving section includes a signal separating section 31, a telephone quality speech decoder 32, a sampling frequency converting section 10, a high quality speech decoding section 36, a selector 37, an echo canceller 23, a D / A converter 38 and an output terminal. It consists of 39.

Hereinafter, a case where a digital audio signal is transmitted and received using the above-mentioned digital audio transmitter and receiver will be described. At the time of transmission, the transmitted voice that is an analog signal is input from the input terminal 21 to the A / D
It is supplied to the converter 22. This analog signal is A / D
After being converted into a digital signal by the converter 22, it is supplied to the echo canceller 23. The echo-removed analog signal output from the echo canceller 23 is converted into the band conversion unit 2 and the high-quality speech encoder 2 according to the encoding method used.
7 is supplied.

As described above, the band conversion unit 2 comprises the band-limiting digital low-pass filter 24 and the 1/2 thinning circuit 25. Only a predetermined band of the signal supplied to the digital low-pass filter 24 is supplied to the 1/2 thinning circuit 25. It should be noted that although the actual sampling frequency becomes low due to the 1/2 decimation circuit 25, the 1/2 decimation circuit 2 is required to satisfy the sampling theorem at that time as well.
A digital low-pass filter 24 is provided in the preceding stage of 5 to limit the band. The band-limited sampling frequency is
For example, the digital signal having a frequency of 8 kHz is code-compressed by the telephone quality voice encoder 26 and supplied to the selector 28 as a code code of 64 kbps.

On the other hand, the digital signal supplied to the high-quality speech coding unit 27 having the same frequency as the operation frequency of the echo canceller 23 (sampling frequency is 16 kHz) is code-compressed and directly usable. Therefore, the code code of 64 kbps coded by the high-quality speech coder 27 is directly supplied to the selector 28.

The code code selected by the selector 28 is supplied to the signal multiplexer 29, multiplexed with the video signal, and output from the digital line via the digital line interface 30.

On the other hand, at the time of reception, the received signal input to the signal separation unit 31 via the digital line interface 30 is separated into a video signal and a code code (audio signal). The code is supplied to the telephone voice decoder 32 and the high-definition voice decoder 36 according to its type, and is decoded and expanded.

The digital audio signal output from the telephone voice decoder 32 is supplied to the sampling frequency converter 10 and converted into the operating frequency of the echo canceller.
As a result, this digital audio signal has the same sampling frequency as that of the digital audio signal output from the high-quality audio decoding unit 36.

As described above, the sampling frequency converter 10
Is a double interpolation circuit 33 and a digital low-pass filter 3.
4 and an amplifier 35. The double interpolation circuit 33 inserts a zero value between the respective sample values in order to formally double the sampling frequency. In this state, a high frequency component is added to the signal. Therefore, the high frequency component is removed by inputting this signal to the digital low pass filter 34 for removing the high frequency component. Further, the output of the digital low pass filter 34 is supplied to the amplifier 35 in order to recover the gain lost by the digital low pass filter 34. This gives a signal of 2
The gain before being input to the double interpolation circuit 33 can be obtained. The output of the amplifier 35 is supplied to the selector 26.

On the other hand, since the sampling frequency of the digital audio signal output from the high-quality audio encoder 36 matches the operating frequency of the echo canceller 23, it is directly supplied to the selector 37. Selector 37
Then, the signal is selected according to the type of encoding method. The selected digital audio signal is output as the received voice from the output terminal 39 via the echo canceller 23 and the D / A converter 38.

FIG. 3 shows a digital low-pass filter 2
The output signal waveforms of the 4 and 1/2 decimation circuits 25 are shown. The waveform shown in FIG. 3A is the waveform of the digital audio signal from the echo canceller 23. FIG. 3B shows the output signal waveform of the digital low pass filter 24. As can be seen from FIG. 3B, the digital low-pass filter 24 outputs a signal having a predetermined band or less. FIG. 3C shows an output signal waveform from the 1/2 thinning circuit 25. In this way, by thinning the sampling frequency of the digital audio signal from the echo canceller 23 by the 1/2 thinning circuit 25, a telephone quality digital audio signal can be formed.

FIG. 4 shows output signal waveforms of the double interpolation circuit 33 and the digital low-pass filter 34. The waveform shown in FIG. 4A is the output signal waveform of the telephone speech decoder 32. FIG. 4B shows the output signal waveform of the double interpolation circuit 33. In FIG. 4B, the waveform indicated by the solid line is the waveform after double interpolation. As can be seen from this waveform, there is a band component (high frequency component) in the signal which is unsuitable for a telephone quality voice signal. FIG. 4C shows the output signal waveform of the digital low pass filter 34. That is, a digital audio signal waveform from which the high frequency components have been removed is shown. This digital audio signal is supplied to the amplifier 35 and its gain is doubled.

The present invention is not limited to this embodiment, and, for example, three sampling frequencies are different.
For digital audio transmitters and receivers that have more than one type of audio encoding system, sampling frequency converters are provided for each and a single echo canceller or an A / D converter or a D / A converter is used. Various modified devices can be implemented.

[0031]

According to the present invention, since the sampling frequencies of the encoding systems having different sampling frequencies can be originally unified, even if the reproduction frequency band is different for each encoding system, one type can be used. It suffices to use only the digital low pass filter of. Further, even if the sampling frequency is different between the transmitting side and the receiving side, the sampling frequency can be unified by using the thinning circuit and the interpolation circuit.
Thereby, the common A / D converter and D / A converter can be used. Therefore, even when performing asymmetric communication,
This circuit can be used. Furthermore, regarding the connection with the outside, the sampling frequency is constant regardless of the encoding method, so even when the signal is directly connected to another signal processing apparatus such as an echo canceller, the information of the encoding method is transmitted to the echo canceller and peripheral devices. Need not tell.

[Brief description of drawings]

FIG. 1 is a principle block diagram of a digital audio transmitter and receiver according to the present invention.

FIG. 2 is a block diagram of a digital audio transmitting device and a digital audio receiving device.

FIG. 3 is a waveform diagram of a band conversion unit.

FIG. 4 is a waveform diagram of a sampling frequency converter.

FIG. 5 is a block diagram showing a configuration of a conventional digital audio transmitter and receiver.

[Explanation of symbols]

 2 band conversion unit 10 sampling frequency conversion unit 24 band limiting digital low pass filter 25 1/2 thinning circuit 33 double interpolation circuit 34 high frequency component removing digital low pass filter

Claims (4)

[Claims] 1. A band conversion means for reducing the band and a sampling frequency of a digital audio signal, a low sampling frequency coding means for a first voice quality, and a high sample for a second voice quality. A digital audio transmitting apparatus comprising: an encoded frequency encoding means; and a selecting means for selecting an encoding code from the low sampling frequency encoding means and the high sampling frequency encoding means. 2. The digital audio transmitter according to claim 1, wherein said band conversion means comprises a digital low-pass filter and a thinning circuit. 3. A low sampling frequency decoding means for the first speech quality, a high sampling frequency decoding means for the second speech quality, and an output signal of the low sampling frequency decoding means. Of the sampling frequency conversion means for increasing the sampling frequency and the selection means for selecting the output signals of the low sampling frequency decoding means and the high sampling frequency decoding means. 4. The digital audio receiving apparatus according to claim 3, wherein said sampling frequency conversion means comprises an interpolation circuit and a digital low pass filter.