The preenFM engine needs a "power of 2" number of samples. The goal of this interpolation is to make it accept any size of waveform.
If your number of sample is a power of 2 (32, 64, 128, 256, 512, 1024), there is no interpolation.
For the rest it interpolates to the closer bigger power of 2.
Source between 33 & 63 => processed waveform will contain 64 samples.
Source between 65 & 127 => processed waveform will contain 128 samples
...
Source between 513 & 1023 => processed waveform will contain 1024 samples
Just realilzed that in 2.02 waveform smaller than 32 are not accepted.
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