Every audio file I've played generated by this (fantastic) extension has had crackling in the first few seconds of music. Try e.g. https://en.wikipedia.org/wiki/User:MarkAHershberger/Music_Sandbox : wait for the player to appear and click play. I'm on Ubuntu and so far only other developers on Linux have confirmed hearing a crackle, so it might be Linux only.
It's not the MediaWiki media player; other .ogg files play fine e.g. https://commons.wikimedia.org/wiki/Audio_files_of_medieval_music , and if I download the .ogg generated by Score it crackles whether I play it in Firefox's built in .ogg player, the rhythmbox player, or the gstreamer pipeline. If I download the .midi file and generate it myself using the same "timidity" MIDI converter that the Score extension uses (e.g. /usr/bin/timidity -Ov --output-file=timidity_out.ogg sample.midi) it has the same crackle. It's not the OGG format: other .ogg files such as /usr/share/sounds/ubuntu/stereo/desktop-logout.ogg play fine, and the crackle remains if I convert to a .wav file instead of a .ogg file.
The real proof that the problem lies in timidity would be to inspect the waveform of the raw output file for crackles.
timidity bug reports suggest using its --output-24bit option for higher quality. For that one sample file the crackle went away if I used both --output-24bit and convert to a .wav file.
Version: master
Severity: major
See Also:
https://bugzilla.wikimedia.org/show_bug.cgi?id=40590