Nortel Networks Corporation

Masoud Ahmadi

Joachim Fouret

Mohamed Samy El-Hennawey

Can Liao

A fast DTMF detector for filtering a packetized linear voice signal to identify whether the voice signal contains a DTMF tone. The detector includes a plurality of parallel notch filters for knocking down DTMF tones. The energies of the filtered signals output by the notch filters are calculated and criteria based upon the calculated energies are applied to determine if the voice signal contains a DTMF tone. The criteria include an energy differential test, a twist test, a low frequency tolerance test, a high frequency tolerance test, a packetized linear voice signal energy level test, a dial tone filtered signal energy level test, and a 1004 Hz filtered signal energy level test.

Method and apparatus for fast DTMF detection

A signalling tone detector for use in a communications network for the detection of dual frequency multi-tone (DTMF) pairs of signal tones in a time division multiplex (TDM) signal. The detector comprises first and second arrays of adaptive notch filters corresponding to the rows and columns of a subscriber's pushbutton key set. Each said notch filter responds to a respective signal tone by the generation of a corresponding output signal. A logic circuit identifies from a combination of output signals from the adaptive notch filters the presence or absence of a pair of signal tones and, when the presence of a pair of signal tones has been identified, for decodes that pair of tones to corresponding digit information. The detector is used in an arrangement for compressing and packetising TDM traffic for transport over a connectionless network. To prevent distortion, the DTMF tones are decoded to digit information prior to transport over the connectionless network.

Dual tone multi frequency signal detection

Tone detection in a telecommunication system uses an auto correlation algorithm to detect pitch period, then matches this with known pitch periods for the tones. Enhanced reliability or speed of detection and reduction in computational load can be achieved. This can improve quality of echo cancellation where cancellers treat tones differently to speech. Similarly with speech coding, since implementation of some coding standards involves tones being treated differently to speech. The auto correlation output can be used both for noise detection and tone detection, to save computational resource.

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Harlow, United Kingdom

Masoud Ahmadi