| 摘要 |
The number of zero-crossings in each band of a dual-tone multifrequency (DTMF) signal is counted and compared with that in immediately preceding measurement periods. The magnitude of any difference is established and when it is at least equal to a threshold value, pref. one, the input signal is considered to be a DTMF signal. - The energy parameter, representative of the tone energy in a signal, is measured in real time in each band, and three threshold values for the difference from average values determined. The measured difference values are compared with the thresholds to determine if a DTMF signal exists. An interference frequency is accepted when occurring in successive measuring periods. |
