An efficient algorithm for DTMF decoding using the subband NDFT

An algorithm based on the subband nonuniform discrete Fourier transform (SB-NDFT) is proposed for decoding dual-tone multi-frequency (DTMF) signals. To decode a DTMF signal, its energy at the eight DTMF frequencies must be determined by evaluating samples of the NDFT at these frequencies. In the proposed SB-NDFT algorithm, these NDFT samples are computed by decomposing the input signal into two subbands. Since DTMF signals occupy the low-frequency part of the telephone bandwidth, the higher subband can be discarded for a fast, approximate computation. A performance comparison between algorithms based on the NDFT, SB-NDFT, DFT, and SB-DFT shows that the SB-NDFT requires the lowest number of computations to attain a specified level of performance