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I am working on a pitch detection project using Unity3D. I am very new to coding, unity & pretty much everything else I'm currently working on! :-) I came across this web page that helped get me going and am using the FFT code in my project:

http://www.kaappine.fi/tutorials/fundamental-frequencies-and-detecting-notes/

It's mostly working really well, however the frequency detected seems to vary depending on which computer I use. I have tried it on various desktops & laptops (mixture of pc & mac), and on some computers it picks up the correct frequency but on others it gives me a frequency of approx. 1.5 semitones flat. What is interesting though is that out of the 6 computers I’ve tried it on, 3 have been correct and the other 3 have all been the same 1.5 semitones flat.

It can't be down to the microphones as I have tried both the built in mics on some computers as well as separate mics and results have not varied.

Does anyone have any idea what could be the reason for this and how I could solve the issue? Any adjustments I could maybe make to the code? The project I am working on will eventually be distributed as an iPhone app so I need it to work universally across devices.

By the way I can only use C# programming language at the moment.

Many thanks in advance for any help & advice

Best wishes

Phil

Philsko
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    Did you check if the sampling rate you use is within the device min/max supported rates (see http://docs.unity3d.com/ScriptReference/Microphone.GetDeviceCaps.html)? – SleuthEye Jun 16 '14 at 23:58

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1.5 semitones happens to be the same ratio as the ratio between sampling rates of 48 kHz and 44.1 kHz. My guess is that you have hard-coded 48 kHz as your sample rate but that some of your computers are actually using a sample rate of 44.1 kHz (or vice versa). You should use a suitable API to determine the sample rate in use, or explicitly set it yourself.

The math:

  • 1.5 semitones is a ratio of 2^(1.5/12) = 1.09.
  • Ratio between 48 kHz and 44.1 kHz = 48/44.1 = 1.09.
Paul R
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    You Legend! That is spot on, exactly what is happening. Just in case anyone else comes across this with a similar problem, I got round it by setting the sample rate in the Start function using: samplerate = AudioSettings.outputSampleRate; as opposed to setting it manually. Thanks so much for your help Paul! – Philsko Jun 17 '14 at 09:59
  • You're welcome - my psychic powers are evidently working well today - I should probably go and place a bet on a World Cup match while I have the chance... ;-) – Paul R Jun 17 '14 at 10:12