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Audio Signal Conditioning Circuit

IP.com Disclosure Number: IPCOM000091074D
Original Publication Date: 1969-Oct-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Abbiate, JC: AUTHOR [+2]

Abstract

The circuit provides for the automatic conditioning of audio signals Discrimination between speech signals and noise is achieved by disconnecting an automatic gain control AGC device when speech is not present The input signal is fed to AGC and also to a full-wave rectifier FWR followed by a smoothing low-pass filter LPF. The output signal of LPF is fed to a maximum follower circuit which detects and holds the maxima of the rectified input signal and to a minimum follower circuit which records the minima of the rectified input signal, i.e., the mean level of noise. The minimum follower circuit output controls variable resistor R1. The latter, together with resistor R2, at the output of the maximum follower circuit is a dividing circuit. Its output is used as a variable threshold input to comparator C.

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Audio Signal Conditioning Circuit

The circuit provides for the automatic conditioning of audio signals Discrimination between speech signals and noise is achieved by disconnecting an automatic gain control AGC device when speech is not present The input signal is fed to AGC and also to a full-wave rectifier FWR followed by a smoothing low-pass filter LPF. The output signal of LPF is fed to a maximum follower circuit which detects and holds the maxima of the rectified input signal and to a minimum follower circuit which records the minima of the rectified input signal, i.e., the mean level of noise. The minimum follower circuit output controls variable resistor R1. The latter, together with resistor R2, at the output of the maximum follower circuit is a dividing circuit. Its output is used as a variable threshold input to comparator C. This receives at its other input the output signal of LPF which is the rectified original input signal. Whenever the rectified original input signal is over the threshold value, switch S is open and AGC transmits an output signal which is speech. However, when the original input signal falls under the threshold value, the input signal is considered as noise. Then comparator C sends an output signal to close switch S and the AGC input is thus grounded.

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