AudioStreamPlayer - `pitch_scale` introduces aliasing

[yankscally]

Tested versions

all versions

System information

win10

Issue description

When using pitch_scale because of the way playback rate resampling works this can introduce audible aliasing artifacts

For example at a sample rate of 44100 the Nyquist frequency is 22050

When pitching audio upward spectral content is pushed beyond this allowed range of 22050 and without a proper band limiting filter these frequencies fold back (Nyquist reflection) into the audible range causing inharmonic distortion

Additionally the current use of linear interpolation for fractional sample positions introduces further waveform distortion generating harmonics even from simple signals like sine waves

A proper solution would require band limited resampling instead of linear interpolation.

In simple terms, adding a special filter before the resample step will fix this

Steps to reproduce

play a sine wave and loop it (runtime/editor doesnt matter)
modulate pitch_scale down to hear crunchy aliasing.
module it up to hear nasty aliasing

Minimal reproduction project (MRP)

n/a

[goatchurchprime]

I made my own audio sine wave generator and I'm not able to recreate the same bad audio we saw on yours.
https://github.com/yankscally/audio_playground/blob/main/audioresample

Try updating that one off the audio playground and checking if that nasty little ringing is still in there.

Is it possible that the sine wave generator you had was bodged or had a little step in it somewhere.

2026-02-09.15-44-43.mp4

[yankscally]

Is it possible that the sine wave generator you had was bodged or had a little step in it somewhere.

Yes. That is what it is
🤦