AVAudioUnitTimePitch: speeding up introduces artifacts

For an upcoming update of one of my apps, I’m facing an issue:

The .rate parameter of a AVAudioUnitTimePitch allows me to slow down an audio track without any issues: setting .rate to 0.7 or 0.8 results in an almost perfect playback without changing pitch.

However, whenever the .rate parameter is greater than 1 (e.g. 1.1 or 1.15), I’m starting to hear audio artifacts (“flattering”) in the audio output which is not so nice (even at .overlap = 32).

Intuitively, I’d’ve thought that speeding up the file should contain less artifacts than slowing it down??

I’ve tried different sample rates (44.1 kHz and 48 kHz), but same result.

Grateful for any input on this 🙏

AVAudioUnitTimePitch: speeding up introduces artifacts
 
 
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