Phase reversal tone detector using DSP

Details Phase reversal tone detector using DSP Phase reversal tone detector using DSP

1997-12-17

2000-04-25

Isen, Forester W.

Telephonic communications

Echo cancellation or suppression

379410, 379411, 379406, H04M 100

Patent

active

060553103

ABSTRACT:
Apparatus to permit recognition of a G.165 sampled tone to allow for disabling an echo canceller determines a phase change in the sampled tone. The apparatus comprises a FIFO buffer which receives an input sampled tone and temporarily stores samples from the input sampled tone on a FIFO basis presenting a delayed sampled tone to an adaptive filter core. The core is also input by the input sampled tone. The adaptive filter core introduces a variable delay to the delayed sampled tone such that a phase difference between the input sampled tone and the output of the adaptive filter core iteratively achieves an integer multiple of 2.pi.. The apparatus includes a filter freezer for, after the phase difference achieves a multiple of 2.pi., freezing the adaptive filter such that the adaptive filter the delay in the signal imposed by the adaptive filter is set regardless of any phase difference thereafter arising between the input sampled tone and the output of said adaptive filter core. A monitor then monitors the input sampled tone and the output of the frozen adaptive filter for a phase change.

REFERENCES:
patent: 4658420 (1987-04-01), Fukushi et al.
patent: 4836675 (1989-06-01), Hendow et al.
patent: 5029204 (1991-07-01), Shenoi et al.
patent: 5418778 (1995-05-01), Cummiskey et al.
patent: 5420921 (1995-05-01), Lahdemaki et al.
patent: 5625684 (1997-04-01), Matouk et al.
patent: 5748752 (1998-05-01), Reames
"A Simple Phase-Reversal Tone Disabler" ICASSP 86, Tokyo, 1986 by Melsa et al. (pp. 2619-2622).

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