US 5,311,589 AGranted

Apparatus and method for audible signaling tone recognition

AssigneeAT&T Bell Laboratories

InventorsRaymond W. Bennett, Joseph G. Klinger, Brian C. Prorok, Rafid A. Sukkar

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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.

Claims16

Dependent claims

A method of detecting dual-tone, multi-frequency (DTMF) indicators and single-tone indicators, said indicators being used in a telephone system to represent unique ones of a plurality of possible audible signaling tones, said method comprising the steps of:

monitoring digitally sampled signals on a digital channel of said telephone system, said monitoring including collecting a frame having a predetermined number of said samples;
determining amplitudes for a preselected plurality of frequencies in said digitally sampled signals;
determining which two of said preselected plurality of frequencies have the highest amplitudes during said frame;
determining from said two determined frequencies having the highest amplitudes whether a DTMF indicator or a single tone indicator is likely to be present in said signals;
if it is determined that a DTMF indicator is likely to be present, comparing said two determined frequencies having the highest amplitudes to a plurality of predefined pairs of frequencies, each of said predefined frequency pairs defining one of said DTMF indicators, and selecting as a multi-frequency candidate the DTMF indicator having as its defining frequency pair, the frequency pair matching said two determined frequencies having the highest amplitudes;
if it is determined that a single tone indicator is likely to be present, comparing a selected one of said two determined frequencies having the highest amplitudes to a plurality of predefined frequencies, each of said predefined frequencies defining one of said single tone indicators, and selecting as a single tone candidate the single tone indicator having as its defining frequency the frequency matching the one selected frequency;
comparing the amplitude of said digitally sampled signals in said frame to an amplitude threshold dependent in a predetermined fashion upon the indicator corresponding to said candidate;
determining a cadence of said digitally sampled signals;
and
delivering an identification of said indicator corresponding to said candidate if said digitally sampled signals satisfies said amplitude threshold and has a cadence corresponding to a predefined cadence for said indicator.

7 more elements

A method for detecting the presence of one of a plurality of dual-tone multi-frequency (DTMF) digits and a plurality of call progress tones in a digital signal and identifying said one of said DTMF digits and said call progress tones if present in said digital signal, said DTMF digits and said call progress tones having one or more predefined frequency components and said call progress tones having a characteristic predefined pattern, said method comprising the steps of:

determining an amplitude for each of a predefined plurality of frequencies in said digital signal;
selecting two frequencies in said signal with the highest amplitudes;
comparing said two selected frequencies with said predefined one or more frequency components of each of said DTMF digits and each of said call progress tones to identify a candidate tone corresponding to one of said DTMF digits or call progress tones;
comparing the amplitude of said digital signal to a predefined amplitude threshold, said predefined amplitude threshold being based on said candidate tone;
determining a measured continuity period of said digital signal;
if said digital signal satisfies said amplitude threshold and is continuous for a predetermined time period, and said candidate tone comprises one of said plurality of DTMF digits, generating an output signal representing said candidate tone;
and
if said digital signal satisfies said amplitude threshold and is continuous for a predetermined time period, and said candidate tone comprises a call progress tone, determining whether a pattern of said digital signal over time matches a predefined pattern, said predefined pattern dependent in a predetermined fashion upon said candidate tone, and generating an output signal representing said candidate tone if said pattern of said digital signal matches said predefined pattern.

5 more elements

Telephone station set apparatus connectable to one or more subscriber channels, said apparatus comprising:

audio means for transmitting and receiving audible voice communication;
switch means for selectively interconnecting said one or more subscriber channels to said audio means;
control means responsive to user actions for controlling the selective interconnection effected by said switch means;
and
digital signal processing means connectable under control of said control means to said one or more subscriber channels, said signal processing means responsive to said control means for detecting and reporting the presence of dualtone, multi-frequency (DTMF) digits and call progress tones in a digital signal on said one or more subscriber channels, said DTMF digits and said call progress tones having one or more predefined frequency components and said call progress tones having predefined patterns, said predefined patterns defining a specific call progress tone when a plurality of call progress tones have the same frequency components, said signal processing means having:
means for determining two frequencies in said signal with the highest amplitudes;
means for comparing said two determined frequencies with said predefined one or more frequency components of each of said DTMF digits and each of said call progress tones to identify a candidate tone comprising one of said DTMF digits and call progress tones;
means for comparing the amplitude of said determined two frequencies to a predefined amplitude threshold, said predefined amplitude threshold being dependent in a predetermined fashion upon said candidate tone;
means for determining a continuity period of said candidate tone;
means for generating an output signal representing said candidate tone, responsive to said candidate tone comprising a DTMF digit, satisfying said amplitude threshold and being continuous for a predetermined time;
means for determining whether a pattern of said candidate tone matches a predefined pattern, said predefined pattern being dependent in a predetermined fashion upon said candidate tone;
and
means for generating an output signal to said control means representing said candidate call progress tone responsive to said candidate tone satisfying said amplitude threshold, being continuous for a predetermined time, and matching one of said predefined patterns.

10 more elements

A telephone switching system comprising:

a plurality of channels;
switch means for selectively interconnecting said plurality of channels;
control means responsive to user actions for controlling the selective interconnections effected by said switch means;
and
digital signal processing means connectable under control of said control means to said one or more channels, said signal processing means responsive to said control means for detecting and reporting the presence of dual-tone, multi-frequency (DTMF) digits and call progress tones in a digital signal on said one or more subscriber channels, said DTMF digits and said call progress tones having one or more predefined patterns, said predefined patterns defining a specific call progress tone when a plurality of call progress tones have the said frequency components, said signal processing means having:
means for determining two frequencies in said signal with the highest amplitudes;
means for comparing said two determined frequencies with said predefined one or more frequency components of each of said DTMF digits and each of said call progress tones to identify a candidate tone comprising one of said DTMF digits and call progress tones;
means for comparing the amplitude of said two determined frequencies to a predefined amplitude threshold, said predefined amplitude threshold being dependent in a predetermined fashion upon said candidate tone;
means for determining a continuity period of said candidate tone;
means for generating an output signal representing said candidate tone, responsive to said candidate tone comprising a DTMF digit, satisfying said amplitude threshold and being continuous for a predetermined time;
means for determining whether a pattern of said candidate tone matches a predefined pattern, said predefined pattern being dependent in a predetermined fashion upon said candidate tone;
and
means for generating an output signal to said control means representing said candidate call progress tone responsive to said candidate tone satisfying said amplitude threshold, being continuous for a predetermined time, and matching one of said predefined patterns.

10 more elements

Dependencies are inferred from the claim text.