AudioEffectPitchShift deteriorates sample quality "without being used"

[rokasv]

Godot 3.0.2 stable + Windows 10

Continuously playing the same sound through the "Effect" bus in this configuration:

...results in the sample changing sound over time, without ever touching pitch_scale, i.e. it's always = 1.0.

[smeikx]

As soon as you activate the effect audio gets processed by an additional algorithm which transforms the original sound; regardless of the effect’s configuration, the input is changed.
A cheap workaround would be to bypass the effect as long as the value is 1. But users could also just not activate the effect as long as they don’t change its value.

Maybe we could tweak the pitch shifting algorithm instead?

For pitch shifting Godot uses SMBPitchShift (servers/audio/effects/audio_effect_pitch_shift.cpp), which states the following:

osamp is the STFT oversampling factor which also determines the overlap between adjacent STFT frames. It should at least be 4 for moderate scaling ratios. A value of 32 is recommended for best quality.

Currently the recommended minimum, 4, is being used. I tried beefing it up to 32 which improved the overall sound quality noticeably, but also added some other artefacts.

I’ll keep playing with the algorithm’s settings until I understand them. Maybe we could expose them in the editor in some way? Maybe through a quality slider?

[smeikx]

I tried beefing it up to 32 which improved the overall sound quality noticeably, but also added some other artefacts.

Turns out these artefacts come from clipping, as the effect makes the output louder.

[SubSage]

Confirming this issue is still alive as of today, using Godot v3.2.stable.official on linux.

[EviTRea]

Just notice this should be the same issue causing #55090

[Calinou]

I can confirm this on master 9d1626b. The audio gets louder and quality is reduced, which is especially noticeable if you accumulate several AudioEffectPitchShift effects together.

Increasing the oversampling value on each of the AudioEffectPitchShifts from 4 to 16 increases CPU usage significantly, causes audible hitches and doesn't improve quality much.

Minimal reproduction project: test_audioeffectpitchshift_master.zip

Original (good)

simplescreenrecorder-2022-02-09_20.20.55.mp4

4 AudioEffectPitchShifts (bad, and gets worse over time)

Volume was manually reduced in the AudioStreamPlayer node to roughly match the original.

simplescreenrecorder-2022-02-09_20.19.41.mp4

[akien-mga]

Reopening as #57985 was reverted due to regressions.

[ronyeh]

Hi!

If any devs on the Godot Audio / Pitch Shifting system need me to help with testing or bug repros, please @ or message me. I've been running into issues with my app regarding pitch shifting and rapidly repeating sound effects, so I am very much interested in seeing the audio system improved.

Thanks for all your hard work. Godot is awesome. :-)