Method and apparatus for detecting dual tone alerting signal in telephone systems
AssigneeZarlink Semiconductor Inc.
InventorPhilip Ching
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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.
Claims35
An apparatus for detecting a dual tone alert signal in a telephone system capable of at least off hook mode operation comprising a processing channel for each tone, each processing channel comprising:
- a bandsplit filter for extracting the tone of interest and attenuating the other tone;
- a comparator for comparing the amplitude of 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 such that said comparator rejects speech and music imitations of said tone.
An apparatus for detecting a dual tone alert signal in a telephone system capable of at least off hook mode operation comprising:
- a prefilter for boosting frequencies between the tones to be detected;
- a processing channel for each tone, each processing channel comprising 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;
- and
- a timing circuit for determining whether detected tones meet predetermined timing criteria.
A method of detecting a dual tone alert signal in a telephone system capable of at least off hook mode operation comprising the steps of:
- for each tone, extracting the tone of interest and attenuating the other tone;
- and
- comparing the amplitude of each extracted tone with a threshold value adapted to the amplitude of the output of said bandsplit filter so as to reject speech and music imitations.
Dependencies are inferred from the claim text.