LMMS / LMMS/lmms

Valve Saturation causes FPE when input signal is very low

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bug upstream
Dominant language
C++
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Description

Steps to reproduce:

  • Drag LB302 to the editor
  • Put Valve Saturation effect on it
  • Set distortion level to maximum and distortion character to minimum.

As soon as you press a note in LB302, there is some slight crackling and then the output of the effect goes completely silent. There is no ILS or NaN on the output, it just simply stays at 0. The only way to restore from this state is to reload the effect.
This happens always if LB302 is producing the sound, no matter how much processing it goes thru before the saturator effect. There is some artifact with OpulenZ and Mallets as well, but at least they don't kill it completely.

Tested on 1.2.2 and master.

Update: Turns out it's not specific to said instruments, it happens generally when the input signal amplitude is very low.

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First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Reproduce the failure in LMMS using LB302 and the Valve Saturation effect with maximum distortion level, minimum distortion character, and a very low input signal. No source file or test is named; trace the effect processing from this reproduction and verify that the output no longer becomes silent or triggers an FPE.

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
35/100

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