Telephonic communications – Supervisory or control line signaling – Signal receiver
Patent
1996-01-18
1997-12-02
Zele, Krista M.
Telephonic communications
Supervisory or control line signaling
Signal receiver
379282, 379283, H04M 150
Patent
active
056944667
ABSTRACT:
An improved dual tone multifrequency (DTMF) or multitone signal detector which more efficiently and reliably detects DTMF signals. The present invention performs twist computations only when the signal has become stable, thus achieving more accuracy and reliability. The DTMF detector receives a plurality of digital samples of a received signal and calculates energy values for each of the plurality of different uncorrelated frequencies. The DSP then determines maximum values of the energy values for each of the two or more frequency groups, referred to as M(1) and M(2), to detect the plurality of tones in the received signal. The DTMF detector then performs improved twist computation and thresholding. The DTMF detector first determines if the M(1) and M(2) values of the respective frame being examined have the same indices. If so, the DTMF detector compares each of the M(1) and M(2) values of the respective frame being examined with the M(1) and M(2) values of the immediately prior frame, referred to as M'(1) and M'(2), and determines if the M(1) and M(2) values of the current frame are greater than the M'(1) and M'(2) values of the prior frame. If the M(1) and M(2) values of the current frame are greater than the M'(1) and M'(2) values of the prior frame, then the DTMF detector calculates a twist value using the maximum energy values M(1) and M(2) for the current frame being examined.
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Bartkowiak John G.
Xie Zheng-yi
Advanced Micro Devices , Inc.
Hood Jeffrey C.
Saint-Surin Jacques M.
Zele Krista M.
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