资 源 简 介
Dual-tone Multi-Frequency (DTMF) signalling is used worldwide in modern telephony to dial numbers and configure
switchboards. It is the tones that you hear when dialling using a standard touch tone telephone.
A DTMF signal consists of the sum of two simultaneous sinusoids - or tones - with frequencies taken from two
mutually exclusive groups. These frequencies were chosen to prevent any harmonics from being incorrectly detected by
the receiver at some other DTMF frequency. Each pair of tones contains one frequency of the low group (697Hz,
770Hz, 852Hz, 941Hz) and one frequency of the high group (1209Hz, 1336Hz, 1477Hz) and represents a unique
symbol. The frequencies allocated to the push-buttons of the telephone pad are shown below:
