JPH05206956A - Pcm signal/sb-adpcm signal identification circuit - Google Patents

Abstract

PURPOSE:To identify a PCM signal and a B-ADPCM signal so as to prevent the deterioration of sound quality by converting an input signal into a linear code, permitting it to pass through a band pass filter and detecting a signal component in a band except for a specified frequency band. CONSTITUTION:When the PCM signal is converted into the linear code in a non-linear/linear conversion circuit 11, the signal component in the band except for 0.3KHz to 3.4KHz frequency bands does not exist. When the SB-ADPCM signal is converted into the linear code in the circuit 11, the signal component in the band except for the 0.3KHz to 3.4KHz bands exists. A difference between a signal passing the band pass type digital filter 12 with the output signal of the circuit 11 is taken. When the size of differential output is detected in a power detection circuit 14, the input signal can be discriminated to be the PCM signal or the SB-ADPCM signal. A switch circuit 15 changes over a system to a PCM signal output terminal 2 or an SB-ADPCM signal output terminal 3 so as to output the signal. Thus, the signal can automatically be discriminated and the deterioration of sound quality can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a discriminating circuit for discriminating between a PCM coded signal and a high-efficiency voice coded signal, and particularly to a PCM signal recommended by CCITT G711 and G722. The present invention relates to a PCM signal / SB-ADPCM signal discrimination circuit for discriminating an SB-ADPCM signal.

[0002]

2. Description of the Related Art Conventionally, this type of PCM signal / SB-AD is used.
An example as shown in FIG. 2 is known as a PCM identification circuit.

In FIG. 2, on the transmission side, a PCM signal is input from the input terminal 4 and SB-ADP is input from the input terminal 5.
CM signal is input and PCM signal and SB are input from the input terminal 6.
A selection signal that determines which of the ADPCM signals is selected is input, and the selection circuit 21 selects the PCM signal and SB-A.
One of the DPCM signals is selected, the bit steal circuit 22 puts the selection signal "1" or "0" in the LSB of the lower bit of the 8 bits, and the signal is sent from the output terminal 7.

On the receiving side, the LSB detection circuit 23 detects the value of LSB from the PCM signal or SB-ADPCM signal input via the input terminal 1, and according to the detection result,
In the switching circuit 15, the PCM signal is output from the output terminal 2, and the SB-ADPCM signal is output from the output terminal 3.

[0005]

However, in the above-mentioned conventional PCM / SB-ADPCM identification circuit, the LS
Since B is bit stealed, there is a drawback that the voice quality is deteriorated.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore, the object of the present invention is to provide a novel PCM capable of eliminating the above-mentioned drawbacks inherent in the prior art.
A signal / SB-ADPCM signal identification circuit is provided.

[0007]

In order to achieve the above object, a PCM signal / SB-ADPCM signal identifying circuit according to the present invention uses a linear code for a PCM signal or an SB-ADPCM signal sent to a receiving side. From the non-linear / linear code conversion circuit for converting into the linear code and the signal of the linear code, 0.
A bandpass digital filter for passing a frequency band of 3 kHz to 3.4 kHz, and a difference circuit for taking a difference between a signal output from the bandpass digital filter and a signal output from the nonlinear / linear code conversion circuit, A configuration is provided that includes a power detection circuit that detects the magnitude of the differential output from the difference circuit, and a switching circuit that sends out a signal input based on the detection result of the power detection circuit to the PCM signal side or the SB-ADPCM signal side. To be done.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will now be described in detail with reference to the accompanying drawings with reference to the accompanying drawings.

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

Referring to FIG. 1, reference numeral 1 is an input terminal to which a PCM signal or an SB-ADPCM signal is input,
11 indicates the signal input from the input terminal 1 by CCITT G
A non-linear / linear code conversion circuit for converting a non-linear code into a linear code by 711, 1.3 kHz to 3.4 kHz.
A band pass type digital filter circuit for passing the z frequency band, 13 is a difference circuit for taking the difference between the output signal of the nonlinear / linear code conversion circuit 11 and the output signal of the band pass type digital filter circuit 12, and 14 is the power of the signal. A power detection circuit for detecting the signal, 15 is a switching circuit for switching the signal input from the input terminal 1 to the PCM signal side or the SB-ADPCM signal side, and 2 is a PC
An output terminal 3 for outputting an M signal is an output terminal for outputting an SB-ADPCM signal.

The operation of one embodiment according to the present invention will be briefly described below.

The PCM signal of CCITT G711 is
Since the signal in the frequency band of 0.3 kHz to 3.4 kHz is represented by a non-linear code of 8 bits, even if the non-linear / linear code conversion circuit 11 converts the signal to a linear code, it is 0.3 kHz.
There are no signal components other than the frequency band of Hz to 3.4 kHz. Meanwhile, SB-ADPC of CCITT G722
The low frequency band of the M signal is 6 bits (5
Bit, sometimes 4 bits), 2 bits A for high band
Since the SB-ADPCM signal is linearly code-converted by the non-linear / linear code conversion circuit 11 as it is because it is converted to a DPCM code and coded to have a total of 8 bits, a frequency of 0.3 kHz to 3.4 kHz is obtained. Signal components are generated in addition to the band.

Therefore, if the signal input from the input terminal 1 is a PCM signal, the bandpass digital filter circuit 1
Since the input signal and the output signal of 2 are almost the same signal, when the power of the difference signal is detected by the power detection circuit 14, a relatively small power is detected.
The PCM signal is determined, and the switching circuit 15 inputs the input terminal 1
The signal input from is output to the output terminal 2 as a PCM signal.

On the other hand, the input signal is SB-ADPCM.
If it is a signal, the input signal and the output signal of the band-pass digital filter circuit 12 are different signals. Therefore, when the power of the difference signal between them is detected by the power detection circuit 14, a relatively large power is detected. , SB-AD
The PCM signal is determined, and the switching circuit 15 inputs the input terminal 1
The signal input from is output to the output terminal 3 as an SB-ADPCM signal.

[0015]

As described above, according to the present invention,
0.3 considering the input signal as a PCM signal
It is possible to detect whether the input signal is a PCM signal or an SB-ADPCM signal by detecting whether or not there is a signal component other than the frequency band of kHz to 3.4 kHz. To not do
The effect that the voice quality is not deteriorated is obtained.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing a conventional example.

[Explanation of symbols]

 1, 4, 5, 6 ... Input terminals 2, 3, 7 ... Output terminals 11 ... Non-linear / linear code conversion circuit 12 ... Band pass digital filter 13 ... Difference circuit 14 ... Power detection circuit 15 ... Switching circuit 21 ... Selection Circuit 22 ... Bit steel circuit 23 ... LSB detection circuit

Claims (1)

[Claims] 1. A non-linear / linear code conversion circuit for converting a PCM signal or an SB-ADPCM signal sent from the receiving side to a linear code, and a frequency band of 0.3 kHz to 3.4 kHz from the signal of the linear code. A band-pass digital filter for passing the signal, a difference circuit for taking the difference between the signal output from the band-pass digital filter and the signal output from the nonlinear / linear code conversion circuit, and the difference from the difference circuit A power detection circuit that detects the magnitude of the output, and a switching circuit that outputs a signal input according to the detection result of the power detection circuit to the PCM signal side or the SB-ADPCM signal side are provided.
CM signal / SB-ADPCM signal discrimination circuit.