LMMS / LMMS/lmms

ZynAddSubFx glitch on high sample rate

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bug
Dominant language
C++
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Description

A rare glitch appears with ZynAddSubFx with very specific scenarios. It Might be related to the envelopes in ZynAddSubFx, but it happens too randomly to be sure.

Steps to reproduce:
- Set the playback sample rate to 192 kHz (currently doable in .lmmsrc.xml)
- Open [this](https://github.com/LMMS/lmms/files/15379792/zyn-bug.mmp.zip) project. (Updated)
- Enable the oscilloscope and press play

Expected behavior:
The sound sounds, then goes to silence.

Actual behavior:
You can see a gradually appearing DC offset in the output.
Putting in a reverb in Zyn produces even more crazy things.

Tested in 1.3.0-alpha.1.606+g75d6be2ea (Linux/x86_64, Qt 5.15.13, GCC 14.1.1 20240507)

Contributor guide

No contributing guide indexed for this repository

Research direction

Start by configuring the playback sample rate to 192 kHz in .lmmsrc.xml, opening the linked zyn-bug.mmp project, enabling the oscilloscope, and pressing play. Compare the output with and without reverb in ZynAddSubFx; done means the gradual DC offset and resulting glitch no longer occur.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
audio-video-rtc
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Needs clarification
Newbie friendliness
30/100

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