Unity Workflow LibraryUWLAbout

Topic 11 · Audio

Mixers, snapshots, ducking and loudness

Route sounds through mixer groups, switch moods with snapshots, duck by routing and keep master below clipping.

Markdown version

How the mixer works

  • An Audio Mixer is an asset with a tree of groups under an always-present Master group. Each AudioSource routes to a group; effects, sends and returns process the group's signal. A mixer's output can be routed into a group of another mixer.
  • Snapshots capture all of a mixer's parameter values; transitioning between them changes mood or theme. AudioMixerSnapshot.TransitionTo(timeToReach) interpolates to the snapshot over that time (reference).
  • Ducking changes one group based on what another group is doing, for example lowering ambience while something else plays.
  • Exposed parameters and snapshots don't mix. Per the SetFloat reference, once AudioMixer.SetFloat sets an exposed parameter, snapshots no longer control it. Do not call it in Awake, OnEnable or AfterSceneLoad; call it in Start or later. It returns false when the parameter is not found.
  • Settings sliders. Expose one volume parameter per user-facing category (music, effects, voice) on the parent group, and drive it with SetFloat. Leave other parameters to snapshots.

MIXER-GRAPH-FROM-CODE

  • There is no public API to add mixer groups or effects. The Editor's internal UnityEditor.Audio.AudioMixerController does it with the calls the Audio Mixer window makes: CreateNewGroup + AddChildToParent; new AudioMixerEffectController(name) + AssetDatabase.AddObjectToAsset + PreallocateGUIDs + AudioMixerGroupController.InsertEffect; SetValueForParameter with names from MixerEffectDefinitions.GetEffectParameters. A Send needs sendTarget plus SetValueForMixLevel(0): it defaults to -80 dB, which is silent. Read the mixer back from disk after saving.
  • Shape that worked: a compressor on Master after the fader as a safety limiter (threshold -6 dB, attack 10 ms, release 150 ms, no make-up gain); under SFX, a Combat group carrying Duck Volume (threshold -30 dB, ratio 4, attack 0.05 s, release 0.6 s) and a Moments group with a 0 dB Send into that ducker. High-priority moments route to Moments and duck combat in the mixer, with no code timer. Keep the exposed volume parameter on the parent group so the settings slider still covers both children. Measured after: master peak -8.2 dBFS, 0 clipped frames.

NEW-GAIN-FIELD-IS-DB

  • A new serialized field loads as 0 on every existing row. A linear "volume" multiplier added that way silences the whole bank. Author per-row gain in dB (0 = unchanged) and jitter as +/- dB and +/- pitch fraction, so the default is today's behaviour.