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Frequency domain incorrect in FFT output - DTMF Decoding program

I am writing a VI to decode a DTMF signal received through the PC microphone.  The frequency domain data is always showing less than 1 Hz.  I am using the Sound Card AutoPower spectrum VI as my building block.
 
 
Thanks!
 
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Hi

I was not able to access the Vi by the path you have mentioned.

I had similar problems with FFT which was showing the maximum peak at another freq. one thing which comes into my mind is are you using the same sampling freq which you used to acquire the data.

Regards,

Nitin


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(VI is apparently located at www.crazymansales.com/ni/dtmffft.vi ,note the extra "f". ;))
 
Anyway, you feed it only a simple 1D array, which has no time information (assumes dt=1).
 
Try to built a waveform containing the correct dt as in the image. See if things improve! 🙂
 
 
 
 

Message Edited by altenbach on 04-17-2006 09:23 AM

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Thanks - looks like that worked.   I appreciate it!!

Eric

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