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Topic: FFT on Arduino, the audio spectrum is cluttered? (Read 6078 times) previous topic - next topic

robtillaart

@ aydingulgun
Please start your own thread and point to this thread (if needed), that way there is only one thread owner.

Thanks,
Rob Tillaart

Nederlandse sectie - http://arduino.cc/forum/index.php/board,77.0.html -
(Please do not PM for private consultancy)

bosleymusic

You should read the appendix of the "Computer Music Tutorial" by Curtis Roads or Appendix C of my master's thesis: http://www.bosleymusic.com/Papers/DonBosleyThesis_06172013_Edit.pdf

Despite some good information in here, there seems to be some broad misconceptions about what the FFT does, and what the resulting numbers actually mean.

polymorph

A word on lowpass filtering for Nyquist: Nyquist essentially says that you should have no (negligible) frequency content at or above 1/2 the sample frequency.

So if the sample frequency is 39ksps, you can't just use an 18.5kHz cutoff filter, because that is only -3dB down at the corner frequency of 18.5kHz, and lets through quite a bit above that.

You need a lower corner frequency and a high enough order filter to drop down the filter passthrough to probably -40dB at 1/2 of the sample rate.
Steve Greenfield AE7HD
Drawing Schematics: tinyurl.com/23mo9pf - tinyurl.com/o97ysyx - tinyurl.com/q7uqnvn
Multitasking: forum.arduino.cc/index.php?topic=223286.0
gammon.com.au/blink - gammon.com.au/serial - gammon.com.au/interrupts

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