I'm using Math.net and Bass.Net to write FX effects for guitars. I'm currently stuck on the the pitch shifter. I have to implement a custom DSP callback function which provides the guitar PCM data and the length in bytes (the sample rate is 44100 Hz). I currently use the FFT implementation of Math.Net, but I don't know what to do with the complex output. My code is the following:

        //buffer (IntPtr) contains the PCM data in 32-bit floating point samples
        //length (int) is the number of bytes to process

        Complex[] cOutput = new Complex[length/4]; //allocate the buffer to store the complex numbers 
        float* data = (float*)buffer;
        for (int i = 0; i < (length / 4); i++)
            cOutput[i] = new Complex((double)data[i], 0.0); //fill the Complex array

        Fourier.Forward(cOutput); //apply the FFT to the filled Complex array and overwrite its data

So I'm now have an array of Complex, but I don't know what part of this array I have to modify to change the pitch. So what comes next in the pitch shifting algorithm?

Thanks for your help


closed as too broad by hotpaw2, MBaz, jojek Aug 21 '17 at 14:49

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  • $\begingroup$ Have you looked up the different methods of time-pitch modification and chosen one? $\endgroup$ – hotpaw2 Aug 20 '17 at 12:15
  • $\begingroup$ No, I haven't found any. Where can I find those? $\endgroup$ – Tom Stuart Aug 20 '17 at 12:33
  • $\begingroup$ Maybe start with dsp.stackexchange.com/questions/tagged/pitch $\endgroup$ – MBaz Aug 20 '17 at 15:26
  • $\begingroup$ I looked there, but I couldn't find anything that could help me with my problem. $\endgroup$ – Tom Stuart Aug 20 '17 at 15:38
  • 1
    $\begingroup$ You will have to do a lot more than "look". Try studying: time pitch modification, PSOLA, phase vocoder, etc. Follow the references. $\endgroup$ – hotpaw2 Aug 20 '17 at 16:50

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