VoIP Voice and Fax Signal Processing

7.5 TONE DETECTION USING TEAGER AND KAISER ENERGY OPERATOR

The TK energy operator is used for generic tone detection. TK is an efficient method that provides faster detection than traditional methods based on Fourier transforms and on the Goertzel algorithm. The TK operator is a frequency modulation (FM)–amplitude modulation (AM) demodulation technique for detecting the presence of a tone with arbitrary frequency and amplitude. It is mainly useful as a DTMF early warning detector to help with DTMF rejection. The design of Teager and Kaiser is given in [Pessoa et al. (2004), Emiya et al. (2004), Kaiser (1990), Fiebrink (2004)]. The TK algorithm is based on a differentiating technique and is hence sensitive to speech and noisy conditions. Some important features of the TK detector relevant to DTMF detection are as follows:

• The TK operator can extract localized frequency of the tone with few samples.
• It can work as a FM demodulator. It can extract localized amplitude envelope and can simultaneously work as an AM–FM detector.
• It works on every new sample.
• It can start working on a minimum of three samples of data. It is a differentiator type of operation. Hence, it cannot add any improved signal-to-distortion discrimination. If the tone is presented along with background noise or disturbance, the analysis is degraded because of the differentiation operation of TK detectors.
• It cannot discriminate between multiple tones in the original form. If two or more tones are presented, it gives ...