| 摘要 |
PROBLEM TO BE SOLVED: To provide a DTMF signal detection system that decides the number of DFT(Discrete Fourier Transform) samples and a frequency point from a sampling frequency and a frequency of a tone signal configuring a DTMF signal so as to detect the DTMF signal. SOLUTION: In the case of detecting 8 tone signals with frequencies of 697, 770, 852, 941, 1209, 1336, 1477 and 1633 Hz by using the DFT, a permissible lower limit frequency fl, a permissible upper limit frequency fh, and a sampling frequency fs of the tone signals are set, the number of DFT samples and a frequency point (k) are decided to satisfy conditions of (k-0.5)fs/N<fs and fh>(k+0.5)fs/N so as to detect the DTMF signal within a permissible range of a frequency deviation of the tone signals.
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