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selecting the best chip

Started by npp January 18, 2006
how do i decide which is the best chip for detection of DTMF tones?
and what does "early" and "delayed" detection mean??

npp wrote:

>how do i decide which is the best chip for detection of DTMF tones? >and what does "early" and "delayed" detection mean?? > > >
Early detection means producing a DTMF event before the length of the digit, and its true validity, can be tested. 10-15ms of tone seems to be the typical point at which these early detectors trigger. There are two reasons I can think of to want early detection. The first is to mute the channel, so the DTMF is not passed through. The second is to create things like RFC2833 events for VoIP. Delayed detection is the normal form, where the true validity of the digit is tested before declaring it to exist. This can be expected to be considerably more resistant to false indications than the early form. DTMF "chips" don't usually offer these features. DTMF software packages to run on general purpose DSPs increasingly do. Regards, Steve
Steve Underwood <steveu@dis.org> wrote in news:dqksgc$slq$1
@home.itg.ti.com:

> npp wrote: > >>how do i decide which is the best chip for detection of DTMF tones? >>and what does "early" and "delayed" detection mean?? >> >> >> > Early detection means producing a DTMF event before the length of the > digit, and its true validity, can be tested. 10-15ms of tone seems to
be
> the typical point at which these early detectors trigger. There are two > reasons I can think of to want early detection. The first is to mute
the
> channel, so the DTMF is not passed through. The second is to create > things like RFC2833 events for VoIP. > > Delayed detection is the normal form, where the true validity of the > digit is tested before declaring it to exist. This can be expected to
be
> considerably more resistant to false indications than the early form. > > DTMF "chips" don't usually offer these features. DTMF software packages > to run on general purpose DSPs increasingly do. > > Regards, > Steve >
The one point that Steve didn't make is that virtually any current DSP has plenty of MIPs to perform DTMF detection. If you are using a programmable DSP, you would pick the DSP for other reasons, (cost, support, additional software requirements, power consumption, etc) -- Al Clark Danville Signal Processing, Inc. -------------------------------------------------------------------- Purveyors of Fine DSP Hardware and other Cool Stuff Available at http://www.danvillesignal.com

Al Clark wrote:


> > The one point that Steve didn't make is that virtually any current DSP > has plenty of MIPs to perform DTMF detection. If you are using a > programmable DSP, you would pick the DSP for other reasons, (cost, > support, additional software requirements, power consumption, etc) >
There is no need for DSP. Any microcontroller will do the DTMF detection algorithm. The lazy folks can use the traditional 8870 clones. VLV
Hello Vladimir,

> > There is no need for DSP. Any microcontroller will do the DTMF detection > algorithm. The lazy folks can use the traditional 8870 clones. >
For those interested in how to squeeze that into a bare bones uC look at TI app note SLAAE16. It's under MSP430. Regards, Joerg http://www.analogconsultants.com