kent@tfd.COM (Kent Hauser) (03/03/91)
Could anyone point me to a sample implementation for toll-quality
tranceivers? Any or all of the above standards would be great.
It would be nice if the implementation used PCM coded data for I/O.
Thanks.
Kent
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Kent Hauser UUCP: {uunet,sundc,uupsi}!tfd!kent
Twenty-First Designs INET: kent@tfd.com
(202) 408-0841 phil@east.Berkeley.EDU (Phil Lapsley) (03/04/91)
If you want chips to do this, several companies make them. The transmitters usually take in four or five bits and produce the analog tones, while the receivers take in the analog tones and produce four or five bits of data. Silicon Systems is one company that comes to mind, but there are others. If you want to implement a transceiver on a general purpose DSP chip, it's not too hard. For the transmitter you just need two tone generators. The receiver is trickier. One possibility is to use ganged bandpass filters followed by a power estimator. Another is to use the Goertzel algorithm, which is essentially a "single frequency" FFT/DFT, on the frequencies of interest. Motorola's "Dr. Bub" bulletin board has the source to a DTMF receiver using the Goertzel algorithm. (I implemented an MF receiver using this technique with Gabriel on a DSP56001 last summer, so I could decode the MF signals at 3:14 into the Pink Floyd song "Young Lust", from their album _The Wall_. If you're curious, the numbers were something like KP + 044 + 831 + ST). References: 1. Geoffrey Smith, "DSP Workshop: DTMF Receiver Using the WE DSP16 Product Family", AT&T DSP Review, Summer 1989, Vol. 2, Issue 3. This is a pretty good overview of the implementation of the Goertzel algorithm for DTMF reception on a DSP16. You can probably get a copy from AT&T at (201) 949-3409. 2. Oppenheim and Schaeffer, _Digital Signal Processing_, Prentice Hall, NJ, 1975, pp. 287-289. Explanation of the Goertzel algorithm. 3. Silicon Systems Communications Products Databook, 1991, Ch. 4 and 5. Data sheets on SSI's DTMF and MF transmitters/receivers/transceivers. You can probably get a copy from SSI at (714) 731-7110. Phil Lapsley phil@ucbarpa.Berkeley.EDU ...!ucbvax!phil