simply using Shannon's law at twice the frequency of the highest component, you won't be able to track the on frequencies near it very well. Sure you can force a result... but it may also respond to whistling and barking dogs. :)

And, what will be left for the microprocessor to do with the remaining activity dutytime? If the micro were cheaper than a DTMF detector maybe... if you didn't need any sort of real accuracy, maybe.

-Jay C. Box