Audio signal transmission system having noise reduction means

Details Audio signal transmission system having noise reduction means Audio signal transmission system having noise reduction means

1984-11-07

1987-06-30

Safourek, Benedict V.

Pulse or digital communications

Repeaters

Testing

333 14, 375 25, 375 34, 455 72, 381106, H04B 1202

Patent

active

046776451

ABSTRACT:
An audio signal transmission system having a noise reduction circuit, which includes a transmission medium such as a magnetic tape to be used to transmit a digital signal converted from an input audio signal and thereafter to output the audio signal reproduced from the digital signal, a digital signal transmitter having a pulse-code modulator and demodulator (MODEM). The noise reduction circuit includes a compressor for compressing the dynamic range of the input audio signal according to the detection level obtained by detecting at least the high-frequency components thereof in order to supply the output from the compression to the digital signal transmitter and an expander for expanding the dynamic range of the demodulated signal from the transmitter according to the detection level of at least the high-frequency components thereof. The transmission system has a low-pass fitler which limits the frequency band of the input signal to be supplied to the dynamic-range compressor to at most half the sampling frequency of the MODEM and thus permits the noise reduction circuit to compress and expand signals supplied thereto in the same frequency band without causing any erroneous operation.

REFERENCES:
patent: 2390641 (1945-11-01), Chatterjea et al.
patent: 3806655 (1974-04-01), Hekimian et al.
patent: 4030129 (1977-06-01), Whitlock
patent: 4271499 (1981-06-01), Leveque
patent: 4381525 (1983-04-01), Senoo et al.
patent: 4404602 (1983-09-01), Hoshimi et al.
patent: 4493091 (1985-01-01), Gundry

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