JPH01204517A - Noise reduction circuit - Google Patents

Abstract

PURPOSE:To prevent the occurrence of breezing by extracting a noise component at reproduction and adding it to a reproducing signal in opposite phase so as to obtain the reproduced output of an original signal. CONSTITUTION:All analog signal is converted into a 12-bit digital signal by an A/D converter connected to a sample and hold circuit 2, the digital signal is given to a digital subtraction circuit 4 and given also to a digital band pass limiter group 5. The sound signal is split into plural band signals, the noise component included in each band signal is extracted by a digital mixer 6 and a difference signal between the noise component and the sound signal is obtained to eliminate the noise component in the audio signal and the signal is processed by using the digital signal. Thus, breezing is avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] This invention relates to a noise reduction circuit used in a tape recorder.

[Prior art] Conventionally, in tape recorders that process analog signals,
The signal-to-noise ratio (S/N ratio) has become a performance problem, and on top of this, modulated 9i4fL sound occurs during recording and playback, causing a loss in the quality of the playback sound. To this end, various noise reduction circuits have heretofore been devised and put into practical use, and have reached the stage where certain effects have been achieved.

[Problems to be Solved by the Invention] However, such conventional noise reduction circuits have the problem of not being able to avoid the breathing phenomenon, and conventional noise reduction circuits do not use an expander during recording and a compressor during playback. The compander used was one type,
There is a problem that there is no compatibility between various methods. Furthermore, when playing back a tape recorded without passing through a noise reduction circuit,
There was a problem in that the frequency characteristics changed when passing through a sound reduction circuit.

[Means for Solving the Problem] Generally, when a signal is recorded, the reproduced signal becomes a signal in which a noise component is superimposed on the original signal.

Possible noise components include tape-specific hiss noise due to discontinuous coupling of tape magnetic materials, bias noise generated during recording, external noise such as hum induced in the playback head, and noise generated in the playback amplifier circuit. It will be done.

Therefore, this invention focuses on the fact that a horn for reproducing the original signal can be obtained by extracting the noise component during reproduction and applying it to the reproduced signal in reverse phase. , the noise component contained in each band signal is extracted and a difference signal between the ′j4F sound component and the audio signal is obtained, thereby removing the noise component from the audio signal and performing the signal processing using a digital signal. , an A/D converter that converts an analog signal into a digital signal, and a plurality of bandpass limiters connected to the A/D converter and having different passbands that output only the lower bits of the digital signal in the divided band. −
, a digital mixer that mixes the outputs of each of the bandpass limiters, and a digital reduction circuit that creates a difference signal of 1d between the digital mixer output and the A/D converter output;
D converting the output of the digital subtraction circuit into an analog signal
This is a noise reduction circuit equipped with a /A converter.

[Example] This invention will be described with reference to an embodiment shown in FIG.

In the figure, 1 is a low-pass filter, 2 is a sample hold connected to the low-pass filter 1, and 3 is an A/D converter connected to the sample hold 2, which converts an analog signal into a 12-bit digital signal.

The digital signal is input to the digital reduction circuit 4 and also to the digital bandpass limiter group 5.

The digital bandpass limiter group 5 includes a plurality of digital bandpass limiters 51 each having a different passband.
52, 53, . . . 5n, and only the lower two bits in each passing band are output.

S/N days without using conventional noise reduction circuit is 60
Since it is about dB, anything below 11 bits is considered to be a noise level, and each digital bandpass limiter 51, 52, 53
,...5□ output can be regarded as the noise level in each band.

The output of the digital bandpass limiter group 5 is input to a digital mixer 6, and noise components over the entire band are output.

The noise component is input to the digital subtraction circuit 4, and a difference signal from the A/D converter is output.

That is, by taking the difference between the output of the A/D converter 3 and only the noise component included in the output, the noise component of the output of the A/D converter 3 is removed and output.

Then, the output of the digital subtraction circuit 4 passes through a D/A converter 7, a sample hold 8, and a low pass filter 9, and is taken out as an analog signal.

Further, the output of the digital subtraction circuit 4 is supplied to other digital circuits as a digital output signal.

[Effects of the Invention] According to the invention described above, only the noise component contained in the input signal can be caused to occur, and the circuit can obtain a noise reduction effect both during recording and/or playback. Furthermore, since it is processed as a digital signal, it is possible to prevent the occurrence of frequency characteristics fluctuations and breathing phenomena.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a noise reduction circuit according to the present invention.

Claims (1)

[Claims] An A/D converter (3) that converts an analog signal into a digital signal, and a plurality of passbands connected to the A/D converter (3) that output only the lower several bits of the digital signal in the divided band. Different digital bandpass limiters (5_1, 5_2, 5_3,...
...5_n), a digital mixer (6) that mixes the output of each digital bandpass limiter (5_1, 5_2, 5_3, ...5_n), and a digital mixer (6) that mixes the output of the digital mixer (6) with the A/ A noise reduction circuit comprising: a digital subtraction circuit (4) that obtains a difference signal from a D converter output; and a D/A converter (7) that converts the digital subtraction circuit output into an analog signal.