METHOD FOR DETECTING DUAL TONE MULTI FREQUENCY(DTMF)

摘要

PURPOSE: A method for detecting dual tone multi frequency(DTMF) is provided to quickly and effectively detect a DTMF by analyzing a frequency component of the DTMF tone and detecting the DTMF when the frequency component is over a specific threshold value. CONSTITUTION: A CPU compares that a detecting indicator is greater than a buffer in a buffer indicator of an IIR filter buffer and is less than a buffer indicator+(Bn-1) when the IIR filter performs a filtering(410,411). A test period is set as a T1 when the detecting indicator is existed between 0 to (Bn-1) of the buffer indicator(421). A Bn number of buffer values are read from each IIR filter frequency buffer and a maximum value is stored in a detecting value(412) when the buffer indicator is located at front over Bn(412). Two maximum values are read among values stored in the detecting buffer(413), and it is judged as to whether two maximum values are over a threshold value(414). The detecting indicator is increased by Bn when two maximum values are over the threshold value(420).