[Danielku15]

Note

AI-authored disclosure (alphatab-ai-authored-v1)

Portions of this content were authored by an AI agent. The agent has read
AGENTS.md and the human submitter accepts responsibility for
compliance with the rules in that document.

Issues

Fixes #2978

Proposed changes

Fade in, fade out and volume swell ramped the channel volume (CC7) and never restored it. After a fade out or volume swell the rest of the track was silent, and changeTrackVolume could not help because it scales that zeroed volume. Fades also ramped from or to the static track volume, ignoring volume automations.

Fades now ramp the expression controller (CC11) instead. The synth multiplies volume and expression, so a fade scales whatever volume is in effect, and volume automations and the track volume keep working. This is also the usual split in MIDI (CC7 for the mixer level, CC11 for performance dynamics), so exported MIDI files behave the same way in other software.

After a fade out or volume swell, the expression is restored when the same voice plays its next non-rest beat, at that beat's real start tick. Restoring at the end of the faded beat would make the release of the faded note audible again (about −7 dB for roughly 250 ms with the default SoundFont) whenever a rest follows. Because generation follows play order, repeats, jumps, triplet feel and grace notes need no extra handling. A following fade beat sets the expression with its own ramp. Single-beat playback restores at the end of the beat.

Known limitations, accepted to keep this simple:

• Expression is per channel: other voices or staves of the same track stay faded until the fading voice plays its next note.
• A note tied out of a faded beat comes back at full level at its tie destination.

Tests cover the fade ramps, the restore after rests across bars, repeats, Scottish triplet feel, a fade out into a fade in, volume automation staying intact, and an audio render checking that the rest after a fade out stays silent and the following notes are audible.

Checklist

• I consent that this change becomes part of alphaTab under its current or any future open source license
• This PR is linked to an accepted issue (see above)
• Changes are implemented
• New tests were added
• I have read AGENTS.md if an AI helped draft any part of this PR

AI authorship disclosure

• No AI agent authored any part of this PR (description, code, tests, or commit messages)
• An AI agent contributed to this PR. The AI-authored disclosure block
  (alphatab-ai-authored-v1) is present at the top of this body, and I have
  personally reviewed every change and can explain each one

Further details

• This is a breaking change
• This change will require update of the documentation/website