Noise reduction system having specific encoder circuitry

Details Noise reduction system having specific encoder circuitry Noise reduction system having specific encoder circuitry

1977-10-21

1980-02-05

Gensler, Paul L.

Wave transmission lines and networks

Amplitude compression and expansion systems

307264, 325 62, 328168, 330126, 330295, H04B 164

Patent

active

041874781

ABSTRACT:
A noise reduction system is provided with an encoder for compressing the dynamic range of an audio input signal in accordance with the amplitude of the input signal and recording the compressed one into a tape-recorder, and a decoder for expanding the dynamic range of a reproduced audio signal from the tape-recorder to the original one in accordance with the amplitude of the reproduced audio signal. The encoder includes a first controlled amplifier circuit in which, when the input audio signal is low- and middle-levels, sufficient emphasis is made to the signal at high-frequencies, and when it is in high-level, the emphasis quantity at high-frequencies is restrictive. The decoder includes a second controlled amplifier circuit having a transfer function related to the character of the first controlled amplifier circuit substantially in inverse-function manner. The first controlled amplifier includes a variable response amplifier having a first resistor connected at one end to an input terminal, a current amplifier with variable gain amplifying current extracted from the other end of the first resistor, a series circuit having a second resistor and a capacitor and connected at one end to the input terminal, and means for adding an output current of the other end of the series circuit with an output current of the current amplifier and means for converting the summed current into voltage directed to an output terminal.

REFERENCES:
patent: 3795876 (1974-03-01), Takahashi et al.
patent: 3815039 (1974-06-01), Fujisawa et al.

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