Flutter Soloud Volume Pan

Volume and pan in flutter_soloud are applied to handles (one per playing voice), not to the loaded AudioSource. Loading a sound gives an AudioSource; each play() returns a SoundHandle you control afterwards. Global volume is engine-wide and multiplies with per-handle volume. Fades, oscillations, and scheduled pause/stop run on the engine's internal fader clock, not on Dart timers.

Minimal example

import 'package:flutter_soloud/flutter_soloud.dart';

Future<void> main() async {
  await SoLoud.instance.init();

  final source = await SoLoud.instance.loadAsset('assets/sfx.ogg');

  // volume and pan can be set at play time...
  final handle = SoLoud.instance.play(source, volume: 0.8, pan: -0.5);

  // ...or changed afterwards on the handle.
  SoLoud.instance.setVolume(handle, 0.6);
  SoLoud.instance.setPan(handle, 0); // 0 = centered

  // Fade out over 2 s, then stop 2 s from now.
  SoLoud.instance.fadeVolume(handle, 0, const Duration(seconds: 2));
  SoLoud.instance.scheduleStop(handle, const Duration(seconds: 2));

  SoLoud.instance.setGlobalVolume(0.9); // master volume, all sounds
}

The API shape

All members of SoLoud.instance. Everything throws SoLoudNotInitializedException if init() has not completed.

Per-handle volume / pan:

• void setVolume(SoundHandle handle, double volume) / double getVolume(handle) — 0.0 muted, 1.0 full. Per-voice gain; multiplies with global volume.
• void setPan(SoundHandle handle, double pan) / double getPan(handle) — -1.0 = full left, 0.0 = CENTER, 1.0 = full right. Diverges from audioplayers (whose setBalance uses the same range) and from just_audio (no pan at all), but trips up models assuming 0..1: setPan(handle, 0.5) is half-right, not "half volume". Debug builds assert the range; release builds clamp to -1..1.
• void setPanAbsolute(SoundHandle handle, double panLeft, double panRight) — sets the L/R channel volumes directly (each -1..1). Bypasses the pan law. Does not affect what getPan returns.

Global:

• void setGlobalVolume(double volume) / double getGlobalVolume() — 0.0..1.0, affects every voice.

Fades (signature: (handle, to, Duration time), global variant omits the handle):

• void fadeVolume(SoundHandle handle, double to, Duration time)
• void fadePan(SoundHandle handle, double to, Duration time)
• void fadeRelativePlaySpeed(SoundHandle handle, double to, Duration time) — ramps playback speed (and pitch, since SoLoud resamples).
• void fadeGlobalVolume(double to, Duration time)

Oscillators (signature: (handle, from, to, Duration time) — time is the full period of one from→to→from cycle):

• void oscillateVolume(SoundHandle handle, double from, double to, Duration time)
• void oscillatePan(SoundHandle handle, double from, double to, Duration time)
• void oscillateRelativePlaySpeed(SoundHandle handle, double from, double to, Duration time)
• void oscillateGlobalVolume(double from, double to, Duration time)

Scheduled actions (engine-clock, no Dart Future.delayed needed):

• void schedulePause(SoundHandle handle, Duration time)
• void scheduleStop(SoundHandle handle, Duration time)

Metering:

• double getApproximateVolume(int channel) — per-output-channel post-mix level for VU meters (channel 0 = left, 1 = right in stereo). Only returns non-zero when visualization is enabled: SoLoud.instance.setVisualizationEnabled(true) first. Returns 0 for an invalid channel index.

Traps

• Simultaneous sounds sum and clip. Two voices at volume 1.0 can exceed full scale and distort; lowering volumes per-sound is a losing battle. The intended fix is the global limiter filter, which caps the mixed output:

  await SoLoud.instance.init();
  SoLoud.instance.filters.limiterFilter.activate();
  // Optionally lower the ceiling (dB, should stay < 0):
  SoLoud.instance.filters.limiterFilter.outputCeiling.value = -3;
  

  See the sibling skill flutter-soloud-filters for filter details.

• Fades/oscillations keep running on stopped handles. If a handle is stopped (or scheduleStop fires) mid-fade, the fader is not cancelled; when the same sound is played again and the handle id is recycled, the old ramp can snap the new voice's volume/pan. Reset the parameter explicitly (setVolume/setPan) when starting a new voice if you previously faded.

• getVolume/getPan/getGlobalVolume round-trip through float. Reading back 0.8 can return 0.800000042353. Never compare with ==.

• Handles die. After a sound ends or is stopped, the handle is invalid. setVolume on a dead handle fails silently on the native side; check getIsValidVoiceHandle(handle) if unsure. Don't cache handles across stop()/scheduleStop().

• getApproximateVolume returns 0 forever if visualization was never enabled — it reads the same analysis buffers as the waveform/FFT feature.

• setRelativePlaySpeed(handle, 0) is undefined behavior (likely crash); the lower bound is silently clamped to 0.05. Same applies to fadeRelativePlaySpeed / oscillateRelativePlaySpeed targets.

• Max voice count is 16 by default. Extra play() calls steal the oldest voice of the same sound (or are dropped with a log warning — no exception), so a fade targeting the stolen handle does nothing. Raise with setMaxActiveVoiceCount if needed.

• Fades are synchronous calls, not Futures. fadeVolume returns immediately; if you need to act when the fade finishes, await your own Future.delayed with the same duration.

More depth

• Limiting and other filters: sibling skill flutter-soloud-filters; demo example/lib/filters/limiter.dart.
• Bus-level volume (group many sounds under one fader): example/lib/mixing_bus/mixing_bus.dart.
• Executable usage references: example/tests/tests/volume_controls.dart, example/tests/tests/pan.dart, example/tests/tests/advanced_pan.dart.

Keeping this skill current

This skill ships inside the flutter_soloud package, so upgrading flutter_soloud can carry a newer revision of it than the copy installed in the project. To check, run:

dart run flutter_soloud:skills --check

It reports the installed and bundled skill versions and exits non-zero when an update is available. Offer to update with dart run flutter_soloud:skills (which touches only the skills, never pubspec or build files).