David Van Horn wrote:

> Decoders are a bit more, but I think you'd be hard pressed to get equal
> performance in all respects, from a software solution, especially if you
> are looking to do anything else in the same processor. Making something
> that sort of works is one thing. Making something that works with good
> dynamic range, twist tolerant, capable of detecting in 40mS, tolerant of
> noise.. That is likely to involve significant development time if it can
> be done at all.

I agree with you Dave, dedicated decoders make the most sense. But, if 
you lack sense or cents, then get insensed here:

http://www.dattalo.com/technical/theory/dtmf.html

I used this technique a long time ago and found that some hardware 
support was still needed to achieve good twist performance and voice 
rejection. Since doing this I've come across another algorithm for the 
magnitude estimator that I suspect will significantly improve the 
performance, but I haven't tried it out.

Scott
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