Brian C Prorok

US Patent:

53115899, May 10, 1994

Filed:

Mar 31, 1992

Appl. No.:

7/860937

Inventors:

Raymond W. Bennett - Naperville IL
Joseph G. Klinger - Sandwich IL
Brian C. Prorok - Naperville IL
Rafid A. Sukkar - Aurora IL

Assignee:

AT&T Bell Laboratories - Murray Hill NJ

International Classification:

H04M 300

US Classification:

379386

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.