Method and device for recognizing tones and sequences thereof

摘要

A method for recognizing tones in a signal in a telecommunication transmission uses samples of the signal to determine whether a tone of an expected frequency and wave shape is contained in the signal. If the method accurately predicts the value of the next sample, then a tone of the expected frequency and wave shape has been detected. Another method may be used to recognize sequences of tones comprising intervals with particular frequencies and durations. The method may be applied to the detection of initiation sequences for fax and modem transmissions, for example the ITU-T recommendation T.30 V.21 fax initiation sequence and the ITU-T recommendation V.25 modem transmission preamble. The method may be incorporated in a device for detecting modem or fax transmissions on a line and routing such modem and fax transmissions to a modem/fax relay. Thus the invention can be used with devices which provide voice compression by ensuring that fax and modem transmissions are not corrupted by being passed through the voice compressors.