Touchtone Phone Code
The touchtone phone is also known as a dual-tone multi-frequency (DTMF) transmitter/receiver.
Each keypress on the keypad generates the sum of two audible sinusoidal tones, where the two
frequencies uniquely define the key that was pressed, as shown below
![](dtmf3.gif)
The A, B, C, D keys appear on service keypads. The tones are typically implemented with
a sampling frequency of 8 kHz.
References
- S. L. Freeny, J. F. Kaiser, and H. S. McDonald, "Some Applications of Digital Signal
Processing in Telecommunications", p.1 in Applications of Digital Signal Processing, A.V.Oppenheim, ed.,
Prentice-Hall, Englewood Cliffs NJ, 1988.
- J. R. Boddie, N. Sachs, and J. Tow, "Receiver for TOUCH-TONE Service",
Bell Syst. Tech. J, 60, 1573 (1981).
- P. Mock, "Add DTMF Generation and Decoding to DSP-microprocessor Designs", EDN,
March 21, 1985.
- A. Mar, ed., Digital Signal Processing Applications Using the ADSP-2100 Family,
Prentice-Hall, Englewood Cliffs NJ, 1990.
Maintained by John
Loomis, last updated 6 Nov 1997