Method and apparatus for detecting dual tone alerting signal in telephone systems
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United States of America Patent
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-
Nov 2, 2004
Grant Date -
Oct 25, 2001
app pub date -
Dec 5, 2000
filing date -
Dec 11, 1999
priority date (Note) -
Expired
status (Latency Note)
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Abstract
An apparatus for detecting a dual tone alert signal in a telephone system capable of at least off hook mode operation includes a processing channel for each tone. Each channel consists of a bandsplit filter for extracting the tone of interest and attenuating the other tone; a comparator for comparing the output of said bandsplit filter with a threshold value; and an adaptive threshold generator for generating said threshold value adapted to the amplitude of the output of said bandsplit filter to reject speech and music imitations. The apparatus offers improved talkdown and talkoff immunity.
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