finding amplitude of a specific frequency

[Alan Anderson]

Originally Posted by EricVanWyk

You may see it refered to as "FFT" for "Fast Fourier Transform". For whatever reason, that extra F got into the lexicon.

The Fast Fourier Transform is a specific implementation, based on powers of two and something called a "butterfly" operation. It's very well optimized for digital computers.

For DTMF decoding, there is an even more specific implementation called the Goertzel algorithm. It simultaneously computes the "DFT" for "Discrete Fourier Transform" at all seven (or eight) frequencies of interest. It's a lot faster than doing a full FFT over the entire range of frequencies.

A quick Google search shows that there's a goertzel MathScript function in LabVIEW. The book Digital signal processing system-level design using LabVIEW appears to have a complete DTMF decoder as one of its lab exercises.