Abstract: 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.

Abstract: 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.

Abstract: A narrowband signal detector has an adaptable filter and controller for controlling the centre frequency and the bandwidth of the filter, to track the narrowband signal. Better control of the filter can be achieved by basing the filter control on a comparison of output and input to the filter. The comparison gives a more direct measure of how well the filter is tracking the narrowband signal. In the case of a notch filter, if there is poor tracking. The control should be biased rapidly towards improved tracking speed. Otherwise, for good tracking, the control should be biased towards accuracy of tracking. This enables speed and accuracy of detection requirements to be met with less computational load. Applications include telecommunications signalling or data tone detection. Multiple narrowband signals can be detected by a cascade of filters.

Abstract: 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.

Abstract: Noise is distinguished from speech signals in a communications network by sampling the traffic to provide consecutive frames of samples. An autocorrelation function is calculated for successive sample frames. Measurements are made of the signal energy and a count of zero crossings of the autocorrelation function for each frame. When the signal is found to comprise white noise/unvoiced speech signals, successive frames are compared so as to determine a measure of similarity of frame energy therebetween, a significant number(e.g. five to ten) of similar frames being indicative of noise. Detection of noise may be used in conjunction with echo cancellation to selectively disable this echo cancellation in the presence of noise and absence of speech.

Abstract: 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.