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Product category: Embedded Software and Operating Systems
News Release from: Adaptive Digital Technologies | Subject: DTMF tone detector for TMS320C6000
Edited by the Electronicstalk Editorial Team on 28 March 2003

DSP-based algorithm cuts
DTMF CPU overhead

Adaptive Digital Technologies has ported its carrier-class DTMF (dual-tone multifrequency) tone detector algorithm to the Texas Instruments' TMS320C6000 DSP family

Adaptive Digital's proprietary algorithm, at less than one half the CPU usage measured in MIPS, offers more than twice the channel density compared with the nearest competitor while maintaining strict compliance with industry specifications Bellcore/Telcordia GR506 and ITU Q455. To the customer this translates to two to three times the number of channels per chip, which in turn equals savings by reducing the amount of chips per system.

DTMF refers to the signal generated when you press a digit on a telephone's touch keypad.

The term DTMF stems from the fact that whenever a telephone pushbutton is pressed, the phone generates two specific tone frequencies that are the algebraic summation of the amplitude of the two frequencies.

Four frequencies are used for the rows and four for the columns, for a total of eight frequencies and 16 possible combinations.

So that a voice can't imitate the tones, one tone is generated from a high-frequency group and the other from a low frequency group of tones.

The complex DTMF tone detect algorithm determines the single generated digit by extracting the two frequencies from the input signal, allowing for tolerances such as frequency offset and distortion such as additive noise, and then checking them to see if together they qualify as one of the digits.

A DTMF detector rejects any tone frequency that is not the sum of one high and one low tone.

This prevents speech and noise signals from being interpreted as DTMF tones.

"We've developed this class of detector because telecomms equipment manufacturers demand carrier-class performance.

For them this translates into customer satisfaction and cost savings in site support", said Brian M McCarthy, President.

"With the C6000 family of DSPs we are able to support two DS3s which translates into pennies per channel".

Adaptive Digital's tone detector has been deployed since 1995, hosted on numerous digital signal processors.

Now the algorithm is available on Texas Instruments' highest performance family of DSPs - the TMS320C6000.

The combination of this extremely efficient algorithm and the high performance of the TMS320C6000 DSP family yields DTMF detection for pennies per channel.

Adaptive Digital uses the same proprietary detector technology in its other signalling tone detector products such as R1, R2 and call progress tone detectors.

Furthermore, Adaptive Digital incorporates these detectors in its G.Pak turnkey voice-over-packet DSP software as well as in its tone relay algorithm.

"Whether developing a tone detector or a high fidelity audio system, an engineer has to trade off cost against specifications", said Scott Kurtz, Vice President of Engineering.

" In the DSP arena, the cost of an algorithm is usually measured in terms of its processor utilisation measured in millions of instructions per second.

Using our proprietary detection algorithm, we have exceeded industry specifications while keeping the 'cost' well below that of any competing technologies".

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