Algorithms for Multi-channel DTMF Detection for the WE DSP32 Family

Steven L. Grant, Missouri University of Science and Technology
J. Hartung
G. L. Smith

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The authors describe two DTMF (dual-tone multiple frequency) detection algorithms that are highly efficient in the use of both real time and memory. The first algorithm is based on linear prediction (LP) and can be used to implement up to 32 DTMF detectors on a single 25-MHz NMOS WE DSP32. Using a 50-MHZ WE CMOS DSP32C, up to 45 detectors can be implemented. The second algorithm is based on a slight modification of the Goertzel algorithm and can be used to implement up to 16 DTMF detectors on a single DSP32 and up to 32 detectors on a DSP32C. In each of these implementations no external memory is used. Thus, for DSP32 implementations, the small 40-pin DIP package can be used. While the LP based algorithm is the more efficient of the two, the modified-Goertzel-based detector performs better in the presence of speech.