Efficient robust DTMF decoding using the subband NDFT

Abstract

Digital dual-tone multi-frequency (DTMF) decoding is often performed by applying a frequency transformation to the received DTMF signal to measure the energies present at the DTMF frequencies. A DTMF decoding algorithm is developed using the concepts of non-uniform frequency sampling and subband decomposition. Since DTMF signals occupy the low-frequency band of the telephone bandwidth, an efficient computation is achieved by retaining only the higher subband in a two-band decomposition of the received signal. Simulations based on the AT&T TouchTone standard are presented to compare the performances of DTMF decoding algorithms based on the subband non-uniform discrete Fourier transform (SB-NDFT), NDFT, SB-DFT and DFT. Results show that the SB-NDFT-based algorithm is more robust to the variation of DTMF frequencies within the specified tolerance bands. Besides, it also requires a significantly lower computational effort to attain a specified level of performance.