Zerberus: use of filter sometimes causes pop noise at the beginning of sample playback

• Jun 8, 2018 - 05:50
S4 - Minor

Sometimes when a filtered sample begins playback, a loud pop is heard at the start of the sample. The pop is loudest when using the 1-pole filters (tested with lowpass and highpass), but it still happens with the 2-pole filters as well, albeit much quieter.

The pops would appear seemingly at random, and usually after playing an instrument for a while via live MIDI input. It took me a while, but I was finally able to make a MuseScore file that reproduces the issue.

Steps to reproduce:
1. Download and extract the following test project: https://drive.google.com/file/d/1DYxi6hmj21uDdXznUO0V6Lf3Nhv0TWtn/view?…
2. Copy "MDL_DrumSet.sfz" and the "MDL_samples" folder to your MuseScore Soundfonts folder.
3. Open "Zerberus_popping_test_03.mscz" in the latest MuseScore nightly.
4. Go to "View" -> "Synthesizer" and click "Load from Score" to load the samples.
5. Play the project in its entirety. There will be no popping noises the first time through.
6. After playback has finished, play the project again.

Result: On the second playthrough, second-to-last line, you will begin to hear loud popping noises at the beginning of each note. The archive includes a video showing this bug in action.

This bug seems similar to the popping issue we were experiencing in Fluidsynth, which was caused by the filter level being set after sample playback had begun. Perhaps it is a similar issue here?

The note that repeats throughout most of the test project is playing the "Snare Rim" articulation, which you can find by searching the MDL_DrumSet.sfz file.