SYSTEM UND VERFAHREN ZUR DOPPELTENVIELFACHFREQUENZDETEKTION DURCH VERWENDUNG VON VARIABLEN RAHMENLÄNGEN

• Main Authors: XIE, ZHENG-YI, BARTKOWIAK, G
• Format: Patent
• Language: German
• Published: 19.09.2002
• Edition: 7
• Subjects: ELECTRIC COMMUNICATION TECHNIQUE; ELECTRICITY; SELECTING

An improved dual tone multifrequency (DTMF) signal detector which uses the Goertzel DFT algorithm and which utilizes variable or differing frame widths that are frequency dependent for improved detection and reduced error. The DTMF detector includes a codec receiver which receives signals from the transmission media, and a digital signal processor (DSP) coupled to the codec. The DSP receives the digital samples and preferably applies the Goertzel DFT algorithm using differing frame lengths according to the present invention. The DTMF detector utilizes a different frame width for different tones of the possible tone frequencies according to the present invention. Thus the calculation uses a different frame length N for different ones of the uncorrelated frequencies, wherein the different frame lengths comprise at least a subset N of the number of digital samples. The different frame lengths N are designed to optimally align the calculated frequency spectrum at each of the different uncorrelated frequencies. The calculation produces an energy value for each of the different uncorrelated frequencies. The DTMF detector preferably multiplies a gain value with each of the energy values to adjust the gain of each of the energy values. After the frequency domain calculation, i.e., after energy values have been calculated for each of the different uncorrelated frequencies, and after any desired gain adjustment, the DSP determines maximum values of the energy values for each of the two or more frequency groups to detect the plurality of tones in the received signal. The DTMF detector also performs various other calculations to ensure valid tone detection.