Method for DTMF tone detection, detection apparatus and telephone device therefor

摘要

The dual tone multi-frequency detection method involves a search being carried out in a low frequency range to find the four frequencies associated with the maximum power output. The process is repeated in a high frequency range. The sum of the maximum power is then compared with the total input power (51) to determine whether the maximum power is nearly equal to the input power to denote a valid tone.