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DTMF Signalling


DTMF Signalling

DTMF stands for Dual Tone Multiple Frequency. It is a tone consisting of two frequencies superimposed. Individual frequencies are chosen such that it is easy to design filters and easy to transmit the tones through a telephone line having bandwidth of approximately 3.5 kHz. DTMF was not intended to be used for data transfer, it was meant to be used for sending the control signals along the telephone line. With standard decoders it is possible to send 10 beeps per second i.e., five bits per second. DTMF standard specifies 50ms tones and 600ms duration between two successive tones.