Subtle transient distortion when time-stretching percussive WAV Drum loops

[samialmesbahi]

first of all, thank you for the library, it’s one of the best time-stretching solutions I’ve tested.

I trying to build application plays drum-only WAV loops.

As soon as the tempo is changed — even by a single BPM increase or decrease — a subtle but audible distortion appears across the entire signal.

The artifact presents itself as transient smearing: the transients are still present, but their clarity is slightly degraded, resulting in a faint residual spectral roughness across the sound.
The closest analogy is the subtle residue left after aggressive noise-reduction processing — the main signal remains intact, but a light digital texture becomes audible.

This artifact appears immediately with any tempo adjustment.

[kupix]

That sounds like expected behaviour, to be honest, for Bungee or indeed any of the open source stretch algorithms. If you could share an example, we can try to improve things.

[samialmesbahi]

I've attached an audio file for you. It plays within the app using the library. At the beginning of the audio clip, the beat plays at its original speed of 90 BPM. In the next clip, I changed the speed by only +1 to 91 BPM. Notice the difference.

wahdeh_by_bungee.wav

[kupix]

Agreed, transients suffer in this example. I don't think this is a bug, it's a limitation of the algorithm: as soon as there's a tempo change, the crispness of transients is lost. Many listeners wouldn't even notice this.

For reference here is the same tempo change with Bungee Pro.

wahdeh_by_bungeepro.wav