Four Ways To Write A Pitch-Shifter example code
This is the code used to produce the audio demos for the ADC22 presentation: Four Ways To Write A Pitch-Shifter. It aimes for simplicity rather than performance.
Organisation
All the different stretching methods are packed into one file. It definitely could be tidier, and I hope to get to that soon - in the meantime, do get in contact if you have any questions about it.
Each class uses a similar streaming-style API. You should be able to instantiate them simply:
HybridPhaseStretch stretch;Configure them with channel-count and block sizes:
double blockMs = 120;
int blockSamples = int(sampleRate*0.001*blockMs);
stretch.configure(channels, blockSamples, blockSamples/4);
Then process blocks:
stretch.setTimeFactor(timeFactor);
stretch.setFreqFactor(freqFactor);
// For `outputBufferSize` output samples, how many input samples should we have?
int inputBufferSize = processor.samplesForOutput(outputBufferSize);
processor.process(inputBufferSize, inputSamples, outputBuffers, outputBufferSize);
processBlocks(stretch, timeFactor);
If you're not performing a time-stretch, then inputBufferSize will always match outputBufferSize.
Dependencies
It depends on my DSP library for a couple of things (to get delay-buffers, FFT and Kaiser windows).
Building
The main logic is in shift-stretch.h.
If you use make, it compiles main.cpp which produces a command-line interface, with built-in help. (I wouldn't recommend focusing on that code - the main stuff is in shift-stretch.h).
FFTs
It's currently written to use a Modified Real FFT, which has a half-bin offset (so we have N complex bins/bands, instead of N-1 complex and 2 real ones). I'd like to change this in future because it's probably more confusing than necessary.
It should be easy to write adapt this to a more typical Real FFT - the main difference should be in bandToFreq(), and perhaps handling the fact that the 0Hz and Nyquist bands will be real.