Multifrequency detection
First Claim
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1. A method of detecting frequencies in a plurality of stored samples in a memory, comprising:
- (a) selectively processing a first subset of said plurality of stored samples to detect a signal of a particular frequency;
(b) selectively filtering a second subset of said plurality of stored samples;
(c) adding said first subset of said plurality of stored samples to said second subset of said plurality of stored samples and storing a plurality of resultant samples in said memory; and
(d) processing said plurality of resultant samples to verify said signal of a particular frequency.
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Abstract
The detection of DTMF tones is improved in a three-step process: first testing even-numbered samples; then testing odd-numbered samples, and finally testing for tone quality (time interval and frequency stability).
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Citations
25 Claims
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1. A method of detecting frequencies in a plurality of stored samples in a memory, comprising:
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(a) selectively processing a first subset of said plurality of stored samples to detect a signal of a particular frequency; (b) selectively filtering a second subset of said plurality of stored samples; (c) adding said first subset of said plurality of stored samples to said second subset of said plurality of stored samples and storing a plurality of resultant samples in said memory; and (d) processing said plurality of resultant samples to verify said signal of a particular frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. Apparatus for detecting frequencies in a plurality of stored samples in a memory, comprising:
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(a) means for selectively processing a first subset of said plurality of stored samples to detect a signal of a particular frequency; (b) means for selectively filtering a second subset of said plurality of stored samples; (c) means for adding said first subset of said plurality of stored samples to said second subset of said plurality of stored samples and storing a plurality of resultant samples in said memory; and (d) means for processing said plurality of resultant samples to verify said signal of a particular frequency. - View Dependent Claims (14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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Specification