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Dual-Tone Multi-Frequency Receiver for Compressed Data

IP.com Disclosure Number: IPCOM000059999D
Original Publication Date: 1986-Feb-01
Included in the Prior Art Database: 2005-Mar-08
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Blokkum, DR: AUTHOR [+2]

Abstract

A dual-tone multi-frequency (DTMF) receiver is a device used to detect touch tones from a telephone. Most PBXs installed use hardware detectors. The figure is a function block diagram of a DTMF receiver which is implemented by mapping into a programmable signal processor. Only one of three samples is used, which reduces the processor time by two-thirds. It also induces a problem of aliasing. That is, all energy over 1600 Hz is folded back into the pass band, and can thereby induce error, degrading performance. It was proven imperially that no errors do occur and that the performance degradation is minor. The decision machine compares the largest input to the sum of the rest. This has two purposes: 1) it rejects voice, and 2) it saves an additional 40% of a traditional decision machine.

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Dual-Tone Multi-Frequency Receiver for Compressed Data

A dual-tone multi-frequency (DTMF) receiver is a device used to detect touch tones from a telephone. Most PBXs installed use hardware detectors. The figure is a function block diagram of a DTMF receiver which is implemented by mapping into a programmable signal processor. Only one of three samples is used, which reduces the processor time by two-thirds. It also induces a problem of aliasing. That is, all energy over 1600 Hz is folded back into the pass band, and can thereby induce error, degrading performance. It was proven imperially that no errors do occur and that the performance degradation is minor. The decision machine compares the largest input to the sum of the rest. This has two purposes: 1) it rejects voice, and 2) it saves an additional 40% of a traditional decision machine. In addition, the dominant tone pairs must pass a minimum threshold to be considered at all. A traditional decision process compares the largest to the next largest and the tone is valid if it is dominant by a factor of 3 or more. The band-edge resonators were designed heuristically, in that they were adjusted about 0.4% to achieve optimum results. The reasons for the design adjustments concerns frequency tolerance. Tones within +/-.5% of nominal must be accepted, and any tone outside 3 3.5% must be rejected. In a mid-band resonator, if a tone is at +3.8% of spec of the 770 Hz tone, the 770 resonator will respond, but the 852 re...