JPH0645836A - Noise reducing device - Google Patents

Abstract

PURPOSE:To provide a noise decreasing device which can effectively decrease noise dispensing with any expensive high-performance A/D converter. CONSTITUTION:This device is provided with an absolute value circuit 2 to be supplied with a digital signal prepared by sampling an analog signal at a prescribed frequency and to obtain the absolute value of this digital signal, integration circuit 3 to integrate the output of the absolute value circuit 2, detection circuit 4 to detect that the output of the integration circuit 3 is lower than a prescribed signal level, and muting circuit 5 to mute the digital signal with the detected output of the detection circuit 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device for improving sound quality in audio equipment and the like.

[0002]

2. Description of the Related Art Audio devices have a problem of noise, which must be reduced as much as possible in order to improve sound quality. On the other hand, in recent years, the digitization of audio equipment has progressed, and so-called DS
Audio signals have come to be digitally processed using P (Digital Signal Processor). This D
In order to perform digital signal processing by SP, an A / D (analog / digital) converter is required as a precondition, but in order to improve the quality of signal processing, a high performance A / D converter should be used. Had to use. Especially when there is no signal, the error of the A / D converter may be emphasized by the DSP and output as noise. To deal with this, an A / D converter having an S / N characteristic with a wide dynamic range is required.

[0003]

However, such a high performance A / D converter is expensive, and there is a problem that the entire apparatus is expensive. This invention
The present invention has been made in order to solve such a problem, and an object thereof is to obtain a noise reduction device that can effectively reduce noise without using an expensive high-performance A / D converter.

[0004]

A digital signal produced by sampling an analog signal at a predetermined frequency is supplied, and an absolute value means for obtaining an absolute value of the digital signal and an output of the absolute value means are integrated. Integration means to
By providing detection means for detecting that the output of the integration means has become smaller than a predetermined signal level and muting means for muting the digital signal by the detection output of the detection means, noise in the absence of signal is provided. Is to reduce.

[0005]

According to the above means, when the analog signal disappears, the noise component is digitally converted and supplied, but the output of the integrating means for integrating the absolute value of the digital signal is higher than that when the signal is present. Since it becomes smaller, the detection output is generated from the detection means. As a result, the muting means mutes the digital signal and outputs it, so that the noise level when there is no signal is reduced.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention,
It is a system configured inside the DSP. Reference numeral 1 is an input terminal to which a digital signal is applied, 2 is an absolute value circuit that takes the absolute value of the input digital signal, 3 is an integrating circuit, 4 is a detecting circuit, and 5 is a muting circuit.

The digital signal of the digitally converted audio signal is converted into an absolute value in the absolute value circuit 2. The absolute value circuit 2 performs, so to speak, rectification, and outputs it as it is when the sign bit of the digital signal is positive data, and when the sign bit is negative data, adds +1 to the complement of the data. Add and output. The integrating circuit 3 to which the output of the absolute value circuit 2 is applied has two delay elements 3-1, 3-2 and three multiplication elements 3-3, 3-4, 3
It is a digital filter composed of -5 and an addition element 3-6, and integrates the output of the absolute value circuit 2.

The detection circuit 4 holds, as reference digital data, a signal level slightly higher than the signal level output from the integration circuit 3 when only a noise component is input, that is, when there is no signal, and the detection circuit 4 stores When the output is smaller than the reference digital data, it is determined that there is no signal, and the detection output is output to the muting circuit 5. The muting circuit 5 performs muting by multiplying the digital signal applied to the input terminal 1 by a predetermined coefficient, and outputs the digital signal as it is when the detection output is not supplied from the detection circuit 4. Then, when the detection output is supplied, the digital signal is multiplied by a constant less than 1 and output. Especially, in the case of completely muting, 0 is multiplied.

Therefore, when an audio digital signal is applied to the input terminal 1, the integrated value of the absolute value of the digital signal is larger than the reference digital data set in the detection circuit 4, and therefore the mu The muting circuit 5 outputs the digital data as it is, but when the result of the integration becomes smaller than the reference digital data in a no-signal state, the muting circuit 5 attenuates the digital signal and outputs it. Therefore, noise is cut. Will be.

It is also conceivable to set a plurality of reference digital data in the detection circuit 4 and change the constant of the muting circuit 5 according to the set reference digital data. In this case, when the integrated value of the integrating circuit 3 becomes smaller than the first reference digital data,
When the constant of the muting circuit 5 is set to a value slightly smaller than 1, and when the integrated value of the integrating circuit 3 becomes smaller than the second reference value, the constant of the muting circuit 5 is further decreased. The muting can be smoothly performed by gradually reducing the constant of the muting circuit 5 each time the reference value becomes small. On the other hand, when the audio signal is applied from the no-signal state, the muting can be smoothly canceled by gradually increasing the constant of the muting circuit 5 by the operation opposite to the above. it can.

[0011]

As described above, according to the present invention,
Since muting is effectively performed when there is no signal, there is no need to use an expensive high-performance A / D converter in the digital audio processing device, and there is an effect that cost can be reduced.

[Brief description of drawings]

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

[Explanation of symbols]

 1 Input terminal 2 Absolute value circuit 3 Integration circuit 4 Detection circuit 5 Muting circuit

Claims (2)

[Claims] 1. An absolute value means that is supplied with a digital signal created by sampling an analog signal at a predetermined frequency, and an integrating means that integrates the output of the absolute value means. A noise reduction device comprising a detection means for detecting that the output of the integration means has become smaller than a predetermined signal level, and a muting means for muting the digital signal by the detection output of the detection means. 2. The detection means has a plurality of detection levels, and the muting level of the muting means is changed according to the detection levels.
The described noise reduction device.