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Does anybody know what the frequency range of auriotouch is in FFT mode? Also, where is it defined in the code if possible. I've been digging through it, but am not very familiar with FFT or frequency calculation so am not having much luck. I've also done some googling and searching on stackoverflow and have not found results there either. Thanks for the help in advance.

Ian Oswald
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  • You might try here first: http://stackoverflow.com/questions/1447059/auriotouch-fft-for-an-instrument-tuner – iwasrobbed Jul 29 '10 at 19:30
  • I read through that one before posting but couldn't really understand it, I thought I would try to just modify the auriotouch to gain a basic understanding of it before I dove in and wrote one from scratch. – Ian Oswald Jul 29 '10 at 20:00

2 Answers2

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An FFT's frequency range is (sampleRate/2)/nbins - (sampleRate/2)

The aurioTouch code doesn't set the sampleRate, but it does get the hardware's sample rate at aurioTouchAppDelegate.mm:300

So, in the case of aurioTouch, the frequency range is going to be half whatever the current hardware sample rate is.

Art Gillespie
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  • So is there a way to set the hardware sample rate within this, I am wanting to sample from 20Hz to 20kHz. – Ian Oswald Jul 29 '10 at 19:58
  • when i execute it and ran a sweep through it, it didn't look like it was displaying the lower frequencies on the graph, almost like it was displaying from 1k - 20k – Ian Oswald Jul 29 '10 at 20:30
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    This is probably because the display scale in aurioTouch is linear instead of logarithmic—a curious choice. – Art Gillespie Jul 31 '10 at 23:00
  • How would I go about converting from a linear scale to a logarithmic scale? Is there a formula that is used or is it just how it is processed within the fft? – Ian Oswald Aug 02 '10 at 14:08
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The default range on the app is from 0 to 22050 but the amplitude around 22050Hz is not accurate. Also, not every frequency is displayed, only every other 21.53Hz (22050/1024) is calculated.

The defaults can be modified from the auriohelper file but doubt you can go anywhere higher than 22.05KHz.

ssj
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