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Automatic Measure and Hold Level Control

IP.com Disclosure Number: IPCOM000091956D
Original Publication Date: 1968-Jul-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 3 page(s) / 48K

Publishing Venue

IBM

Related People

Hellwarth, GA: AUTHOR [+4]

Abstract

In computer-based communication systems, it is often necessary to automatically control the level of incoming signals received from telephone lines. In many automatic level control or gain control devices, controls vary signal amplitude during the presence of the entire signal and introduce a certain amount of signal and spectrum distortions. These result from amplitude changes in the signal.

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Automatic Measure and Hold Level Control

In computer-based communication systems, it is often necessary to automatically control the level of incoming signals received from telephone lines. In many automatic level control or gain control devices, controls vary signal amplitude during the presence of the entire signal and introduce a certain amount of signal and spectrum distortions. These result from amplitude changes in the signal.

This automatic level control does not alter signal amplitude during the time that an utterance is being processed. The initial portion of the signal is utilized for setting the level since this signal portion is not needed for processing. Then the level, once set, is held until the utterance is completed. The portion selected for setting the level is as short as possible. However, it is long enough to provide a meaningful measurement.

The technique selects the first natural amplitude boundary for the measurement period. However, a fixed time can be used following the detection of the beginning of the utterance. During the initial interval, the automatic level control operates in a conventional manner. When the first part of the signal occurs, the gain established by the automatic level control at that time is held constant for the remaining portion of the utterance. Thus, for pattern recognition the analysis begins on that portion of the signal occurring after the first pause which would, at this point, be under a constant gain condition.

A conventional automatic level control circuit of the averaging type is shown. The circuit includes a variable gain amplifier, a full-wave rectifier, an averaging circuit, a reference threshold and a comparator amplifier. Switch S, placed between the full-wave rectifier and the averaging circuit, is an additional element to the conventional automatic level control. Switch S is operated by a timing circuit which closes the switch at the onset of signals and opens it again upon occurrence of the first pause in the...