Telephonic communications – Supervisory or control line signaling – Signal receiver
Patent
1992-03-31
1994-05-10
Dwyer, James L.
Telephonic communications
Supervisory or control line signaling
Signal receiver
H04M 300
Patent
active
053115899
ABSTRACT:
A method and apparatus for detecting dual-tone, multi-frequency (DTMF) digits and call progress tones by determining the amplitudes of preselected frequencies in a signal over a predetermined time period, and determining a candidate tone by selecting two of the preselected frequencies with the highest amplitudes and comparing the two selected frequencies to known DTMF and call progress tone frequencies. The amplitudes of the two selected frequencies are then tested against predefined thresholds corresponding to a candidate tone having the two selected frequencies. The candidate tone in the current time period is tested against candidate tones in previous time periods for consistency. If the candidate tone is a DTMF digit and passed all of the tests, then the DTMF digit is returned. If the candidate tone is a call progress tone, the pattern of the candidate tone over a plurality of predetermined time periods is recorded and tested against known patterns of the candidate tone. If the candidate tone meets all of the above tests, the call progress tone is returned.
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Linear Prediction Based DTMF Detection for the WEDSP32 Digital Signal Processor Family, 1989 (Submitted in serial #07/857552).
Bennett Raymond W.
Klinger Joseph G.
Prorok Brian C.
Sukkar Rafid A.
AT&T Bell Laboratories
Dwyer James L.
Johannesen Michael B.
Smith Creighton
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