Classification of audio signals on a telephone line
AssigneeInternational Telesystems Corporation
InventorCharles A. Baldi
Life of this patent
Estimating the term…
Abstract
This telephone solicitation system provides automatic dialing and call-progress detection. Audio signals on the line are analyzed to recognize network operation tones, noise bursts, and speech. A "sample" is the total number of crossings during a 25 millisecond period. A "window" is a sequence of eight samples analyzed for spectral and time patterns.
Claims21
A method of classification of audio signals, including call progress tones and voice, on a telephone line comprising the steps of:
- sampling an audio signal by counting the number of zero crossings of the signal during a predetermined time period to generate a first value;
- using said first value as an index into a first array in which are stored band numbers corresponding to a plurality of possible values to produce a band number corresponding to said first value;
- addressing with said band number of second array in which are stored counts corresponding to said band numbers to increment a count corresponding to said band number;
- testing said count to determine if a threshold is exceeded to classify the audio signal as a call progress tone;
- and
- examining a number of bands and directions of changes of bands to classify the audio signal as voice.
A method of classification of an audio signal on a telephone line comprising the steps of:
- analyzing a predetermined number of successive samples of the audio signal, said predetermined number of successive samples defining a window;
- assigning a band number to each of said samples of said window based on said step of analyzing;
- and
- using said band numbers to classify said window into one of several possible results including an answer, a telephone call progress signal, a computer modem or facsimile tone, or noise.
A method of timing the progress of tones on a telephone line to classify the outcome of a call from a range of possibilities including answer, busy, ringing or noise comprising the steps of:
- analyzing all possible progress of tones on the telephone line as a hierarchy with a large number of results possible at the start of a call but a greatly reduced number of results after only one or two instances of tone/quiet times;
- determining from a duration of said tone/quiet times a progress analysis path to follow in said hierarchy;
- and
- returning within a predetermined period of time a classification of the outcome of the call, otherwise returning a timeout indication.
A method for classifying as an audio signal within a predefined frequency bandwidth comprising the steps of:
- dividing said predefined frequency bandwidth into a plurality of smaller frequency ranges called bands;
- sampling said audio signal and assigning each sample to one of said bands corresponding to its frequency;
- analyzing a number of times successive samples change direction from a higher to a lower frequency band or from a lower to a higher frequency band;
- and
- analyzing the width of a frequency range of said samples and classifying said audio signal according to said number times successive samples change direction and said frequency range width.
Dependencies are inferred from the claim text.