Quote:
Originally Posted by kamocat
I'm trying to make a DTMF decoder with LabVIEW. However, I want it to be able to handle the possibility of several signals overlapping, instead of just assuming it's the first one it finds.
To do that, I need to find the amplitude of a 7 predefined frequencies.
My question is, what is the most efficient way of doing this?
Should I separately filter out each frequency with strict tolerances, and then analyze each filtered waveform to find the frequency of greatest amplitude?
(Doesn't sound very efficient)
Or should I use "Extract single tone information.vi" without filtering, and just enter the frequency I'm looking for in the "advanced" cluster? (I'm assuming a +- 5% band would be tight enough)
Or should I look for the highest peak in the waveform, generate a waveform of the desired frequency, and somehow correlate the two waveforms? (say, subtract or divide, and then look at the remaining variation in frequency)
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I think you are looking for a "Fourier Transform". It converts a time-domain signal to a frequency-domain signal. Basically, it is the efficient method of "separately filter out each frequency with strict tolerances, and then analyze each filtered waveform to find the frequency of greatest amplitude" you mentioned.
You may see it refered to as "FFT" for "
Fast Fourier Transform". For whatever reason, that extra F got into the lexicon.
Apply an FFT to your signal, and look at the amplitudes of the frequencies you care about. Remember to take the absolute value of the amplitude, because you don't care about phase information.