JP3071655B2 - Abnormal noise generation prevention circuit of receiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an abnormal sound generation preventing circuit used in a communication device of a voice coded communication system.

[0002]

2. Description of the Related Art In a voice communication device, due to deterioration of a signal in a transmission path, an abnormal sound (such as an impulsive sound) is generated in a received and reproduced sound.
May occur. In particular, in a speech coding system using a speech codec, this phenomenon appears remarkably. Therefore, an abnormal noise generation prevention circuit is used in the receiver to determine whether the audio signal is an abnormal noise due to a transmission error and to prevent the abnormal noise from being output as it is.

FIG. 2 is a block diagram showing an example of a conventional abnormal noise generation prevention circuit. The received signal “a” output from the demodulator or the audio decoder is input to the continuous overflow detector 1 and the sudden change amplitude detector 5. The continuous overflow detector 1 determines that the input signal a has a normal output dynamic range of the demodulator or audio decoder per unit time (for example, 5 m).
s) Detecting how much the time or the number of times it exceeds, detecting the abnormal sound when the value exceeds a preset threshold value, and outputting a flag b indicating normal sound or abnormal sound I do. The sudden change amplitude detector 5 is provided at a certain interval (for example, 125 μm) within a certain unit time (for example, 5 ms).
When the amplitude difference of the signal sampled in s) exceeds a preset threshold value, a process for deeming an abnormal sound is performed, and a flag f indicating a normal sound or an abnormal sound is output.

In an OR (OR) circuit 6, the input 2
If at least one of the two signals (flags) b and f indicates abnormal noise, the attenuator 4 is operated to output a control signal g for attenuating the input signal a. 4 to output a control signal g for setting the bypass mode. Here, the attenuator 4 outputs the audio output h which gives a certain amount of attenuation to the input signal a in accordance with the control signal g from the OR circuit 6, or enters the bypass mode in which the amount of attenuation becomes zero so that the input signal a As it is as the audio output h.

[0005]

According to such a conventional abnormal sound generation preventing circuit, even if the input signal a is a signal that has already overflowed at the input of the transmitter (for example, an over-input vowel), the abnormal signal is generated. There is a disadvantage that the sound is determined to be sound and the output sound is interrupted.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described conventional circuit, in which a large output vowel is interrupted when a vowel having a high power is input on the transmission side, and the original abnormal noise is eliminated. It is an object of the present invention to provide an abnormal noise generation prevention circuit that can prevent only the generation of (shock noise).

[0007]

According to the present invention, an abnormal sound generation preventing circuit for a receiver outputs an input signal from a demodulator or a speech decoder with a predetermined amount of attenuation in accordance with an externally applied control signal. An attenuator that outputs in the bypass mode or passes as it is, and determines whether or not the input signal exceeds a normal output dynamic range of the demodulator or the audio decoder by a predetermined threshold value, A continuous overflow detector that outputs a flag indicating whether a normal sound is equal to or less than the threshold or an abnormal sound that exceeds the threshold, and a periodicity of the input signal is monitored by monitoring a periodicity of the input signal. A non-vowel detector that outputs a flag indicating whether there is no non-vowel, a flag indicating an abnormal sound is output from the continuous overflow detector, and a flag indicating the non-vowel is output from the non-vowel detector And a logical product circuit for providing a control signal for providing a predetermined amount of attenuation to the attenuator when the attenuator is turned off, and providing a control signal for setting the attenuator to a bypass mode otherwise. It is.

Further, the non-vowel detector uses a part of the algorithm of the speech decoder.

[0009]

FIG. 1 is a functional block diagram showing an embodiment of the present invention. The difference from the prior art is that the non-vowel detector 2 is provided in place of the conventional sudden change amplitude detector 5, and the OR circuit 6 is replaced by the AND circuit 3. Next, the operation of this embodiment will be described. The input signal a output from the demodulator or the audio decoder is input to the continuous overflow detector 1 and the non-vowel detector 2. The continuous overflow detector 1 detects how much the input signal “a” overflows the normal output dynamic range of the demodulator or the audio decoder per unit time (for example, 5 ms), and detects the time or the number of the overflow. When a predetermined threshold value is exceeded, a process for deeming an abnormal sound is performed, and a flag b indicating normal sound or abnormal sound is output. The non-vowel detector 2 detects a certain unit time (for example, 5
In ms), the periodicity is determined by the correlation operation, and if there is no periodicity, a process is considered to be a non-vowel, and a flag c indicating a non-vowel or a vowel is output.

The logical product (AND) circuit 3 receives the input 2
If the two signals (flags) b and c are non-vowels and show abnormal sounds, the attenuator 4 is operated, and if not, a control signal d for setting the attenuator 4 to the bypass mode is output.
Here, according to the control signal d from the AND circuit 3, the attenuator 4 outputs a sound output e that gives a certain amount of attenuation to the input signal a.
Or a bypass mode in which the amount of attenuation becomes zero, and the input signal a is output as it is as the audio output e.

[0011] As described above, in order to prevent the generation of abnormal sounds by monitoring the output level of non-vowels by utilizing the fact that voice does not have much power except for vowels. To avoid the drawback of the technology that even when a signal overflows at the input on the transmitter side (for example, an over-input vowel), the reception side determines that the signal is abnormal and the reproduced output audio is interrupted. Can be.

In a system having a speech decoder, a non-vowel detector can be used by using a voiced / unvoiced decision result (presence or absence of periodicity) which is a part of the next speech codec decoding algorithm. There is also an advantage that the circuit scale can be reduced.

[0013]

As described in detail above, according to the present invention, even when a signal has overflowed at the input of the transmitter (for example, an over-input vowel), the signal is not determined to be abnormal. The reproduction output sound on the receiving side is not interrupted. In a system having a speech decoder, a non-vowel detector can be used by using a voiced / unvoiced decision result (presence / absence of periodicity) which is a part of the next speech codec algorithm. There is also the advantage that it can be reduced.

[Brief description of the drawings]

FIG. 1 is a functional block diagram of an abnormal sound generation prevention circuit according to the present invention.

FIG. 2 is a functional block diagram of a conventional abnormal sound generation prevention circuit.

[Explanation of symbols]

 Reference Signs List 1 continuous overflow detector 2 non-vowel detector 3 AND circuit 4 attenuator 5 sudden change amplitude detector 6 OR circuit

Continuation of front page (56) References JP-A-63-172528 (JP, A) JP-A-64-12658 (JP, A) JP-A-2-299324 (JP, A) JP-A-7-225600 (JP) , A) Fully open 1986-97238 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04B 1/10 H04B 3/20-3/23 H04B 14/00-15/00

Claims (2)

(57) [Claims] 1. An attenuator for outputting an input signal from a demodulator or an audio decoder with a predetermined amount of attenuation in accordance with a control signal given from the outside and outputting the signal in a bypass mode, or outputting the signal in a bypass mode. It is determined whether or not the signal exceeds a normal output dynamic range of the demodulator or the audio decoder by a preset threshold value, and a normal sound below the threshold value or an abnormal sound exceeding the threshold value is determined. A continuous overflow detector that outputs a flag indicating whether the input signal is periodic, and a non-vowel detector that monitors the periodicity of the input signal and outputs a flag indicating whether it is a periodic vowel or non-periodic non-vowel. A control to provide a predetermined amount of attenuation to the attenuator when a flag indicating abnormal noise is output from the continuous overflow detector and a flag indicating the non-vowel is output from the non-vowel detector And an AND circuit for providing a control signal for setting the attenuator to the bypass mode at other times. 2. The circuit according to claim 1, wherein said non-vowel detector uses a part of an algorithm of said speech decoder.