JPH04252521A - Adaptive noise reducing device - Google Patents

Abstract

PURPOSE:To realize the adaptive noise reduction device able to reduce noise due to a code error even in any code error rate by discriminating the code error rate in real time and adjusting an output level in response to the discrimination level. CONSTITUTION:A code error detection section 5 detects a code error in an input data and a timer section 6 measures a code error lapse time T1 based on the detection and a latch section 7 obtains a time interval T2 from a preceding code error and compares the times T1, T2 to discriminate a bit error rate and the result of discrimination controls a D/A converter and an amplifier section 9 receiving the relevant input data.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adaptive noise reduction device used to reduce audio noise caused by code errors in the encoding section of an audio PCM transmission device.

0002

2. Description of the Related Art Conventionally, there are two typical noise reduction devices for reducing voice noise caused by code errors in a decoding section of a voice PCM transmission device.

The first method is to control the output signal only when a code error (for example, a parity error) is detected. This method replaces (pre-holds) the audio data with the original audio data.

The second method is to control the output signal when the bit error rate exceeds a certain value. For example, when the bit error rate exceeds a certain value, the output signal is fixed and only the DC component is controlled. This method performs mute processing as follows.

[0005]

[Problem to be Solved by the Invention] Since the conventional noise reduction device is configured as described above, in the first example shown as a representative example, if the code error rate is low, it is useful for reducing voice noise. However, when the bit error rate becomes high, there is a problem in that even if the pre-hold is used, the noise is not reduced much. In the second example, when the bit error rate is below a certain level, the audio noise is output as is, and there are problems such as it takes time to calculate the bit error rate. There was a problem that it could not be applied.

[0006] This invention was made to solve the above problems, and by determining the code error rate in real time and adjusting the output level according to the determination level, it is possible to Another object of the present invention is to obtain an adaptive noise reduction device that can reduce noise caused by code errors.

[0007]

[Means for Solving the Problems] An adaptive noise reduction device according to the present invention has a code error detection unit and a timer unit that measures the time since the error detection, and the code The elapsed time T1 since the error,
A bit error determination circuit is provided to obtain the time interval T2 of code errors and calculate the bit error rate based on these,
The output signal is controlled according to the determination result.

[0008]

[Operation] The bit error rate determining circuit according to the present invention can determine the bit error rate in real time based on the elapsed time T1 from the code error and the time interval T2 between the code errors. Furthermore, since the output signal is controlled based on the determination result, noise such as audio noise in the case of various bit error rates can be reduced.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is an encoding section of the PCM transmission apparatus, 2 is a decoding section of the PCM transmission apparatus, and 3 is an encoding section 1.
This is a transmission path for transmitting audio data as input data from the decoder 2 to the decoder 2.

In the decoding unit 2, 4 is a transmission line interface to which the audio data from the transmission line 3 is input, 5 is a code error detection unit that detects code errors in the audio data from the transmission line interface 4, and 11 is a code error. The code error detection pulse obtained from the detection unit 5, 6 is a timer unit which is operated by the code error detection pulse 11 and outputs the code error elapsed time T1, and 7 is operated by the code error detection pulse 11 and is before the code error elapsed time T1. The time interval T from the code error of
2, a latch unit 8 compares T1 and T2, determines the larger range, and outputs a control signal 12 according to the determination result; 9 receives audio data from the transmission line interface 4; After converting into an analog audio signal, it is amplified and the D/A conversion and amplification part is controlled by the control signal 12 as an output signal control section, 10 is D
This is an analog audio signal output from the /A conversion and amplification section 9. Note that the bit error rate determination circuit is constituted by each section 5, 6, 7, and 8.

FIG. 2 shows the configuration of the timer section 6, in which 21, 2
2...26 are retriggerable monostable multivibrators whose time constants are set successively smaller.

FIG. 3 shows monostable multivibrators 21 to 2.
6 is a timing chart showing the output pulse of No. 6 and the code error detection pulse of No. 6;

Next, the operation will be explained.

Digital audio data input through the transmission line 3 is terminated at a transmission line interface section 4. A code error detection unit 5 detects a code error from the terminated audio data. When a code error is detected, the code error detection pulse 11 is loaded into the timer unit 6, and the code error elapsed time T1 is measured. Further, the elapsed time T1 outputted from the timer section 6 is latched by the latch section 7 by the code error detection pulse 11. This latched value becomes the time interval T2 from the previous code error. The comparison/determination section 8 compares the code error elapsed time T1 outputted from the timer section 6 and the code error time interval T2 outputted from the latch section 7, and selects the larger value. Then, by checking in which range the selection result falls, a real-time bit error rate (error detection rate) is determined, and a corresponding control signal 12 is input to the D/A conversion and amplification section 9. The D/A conversion and amplification section 9 performs D/A conversion on the audio data output from the transmission line interface section 4, and then amplifies it. In addition, the judgment result (control signal 1
2) The output signal is controlled based on. Then, an analog audio signal 10 is output from the D/A conversion and amplification section 9.

As shown in FIG. 2, for example, the timer unit 6 is composed of monostable multivibrators 21 to 26 having a retrigger function operated by the code error detection pulse 11, and the output pulse width of each monostable multivibrator 21 to 26 is This can be easily achieved by sequentially reducing the size of the image as shown in FIG.

The simplest method for controlling the output signal (analog audio signal 10) is to control the gain of the output signal amplifier of the D/A conversion and amplification section 9. In this method, the gain may be increased as the code error elapsed time T1 or the code error time interval T2 becomes larger.

In the above embodiment, in order to determine the real-time bit error rate, the code error elapsed time T1
The bit error rate is determined by comparing the code error time interval T2 and the range in which the larger value falls, but it is also possible to compare the values obtained by multiplying T1 and T2 by the coefficient α (α≠0). good.

In addition to the method of changing the amplitude of the analog signal as a method of controlling the output signal, the following two methods are effective.

One method is to change the cut-off frequency of the low-pass filter at the output stage. Since noise becomes high frequency due to code errors, lowering the cutoff frequency in proportion to the bit error rate is quite effective in reducing noise and allows a constant audio signal to be transmitted.

The second method is to control the input data of the D/A converter. For example, shift the upper bits to the lower bits by several bits depending on the bit error rate,
A fixed bit is inserted into the blank upper bit. This allows the output level to be adjusted.

Further, in the above embodiment, the case of an audio signal has been explained, but a video signal may also be used, and the same effects as in the above embodiment can be obtained.

[0023]

[Effects of the Invention] As described above, according to the present invention, the code error rate is determined based on the elapsed time from a code error in input data and the code error time interval, so the circuit configuration is simple. This has the effect of reducing noise caused by code errors at low cost.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a noise reduction device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a timer section of the device.

FIG. 3 is a timing chart showing output pulses of the timer section.

[Explanation of symbols]

5 Code error detection unit 6. Timer section 6. Timer section 7 Latch part 8 Comparison and judgment section 9 D/A conversion and amplification section 10 Analog audio signal 11 Code error detection pulse 12 Control signal T1 Code error elapsed time T2 Code error time interval In addition, in the figures, the same reference numerals indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A code error detection section for detecting a code error in input data, and a timer section operated by the detection, and detecting a previous code error based on the code error elapsed time obtained from the timer section and the detection. a bit error rate determination circuit that determines the bit error rate from the code error elapsed time and the time interval; An adaptive noise reduction device comprising an output signal control section that is controlled according to a determination result of a determination circuit.