How do GameMaker audio buses work?

AudioBus assets define a signal chain of effects (gain, lowpass, reverb, etc.). Sounds played with a bus parameter route through that chain before mixing to master. Buses can also send to other buses for complex routing.

Why does the bus effect not affect my sound?

Most likely: audio_play_sound was used without the bus parameter, so the sound bypasses the bus and goes straight to master. Use audio_play_sound_ext or set the sound’s default bus in the sound asset properties.

What's audio_bus_get_emitters?

Returns the audio emitters currently routed through a specific bus. Useful for debugging routing: if the array is empty, your sounds aren’t actually using the bus you think they are.

Fix: GameMaker Audio Bus Effect Not Applied

Quick answer: Use audio_play_sound_ext with the bus parameter, or set Default Audio Bus on the sound asset itself. Sounds without an assigned bus skip the effects chain entirely.

An underwater area should apply a low-pass filter to all sound effects. You created an AudioBus with a LowPass effect; routed master through it. Sounds play but unfiltered. The bus exists; the effect is configured; the routing doesn’t reach the sounds.

How Buses and Sounds Connect

An AudioBus is a routing destination. Sounds choose their bus either:

Per-play via audio_play_sound_ext(sound, priority, loop, gain, offset, pitch, listener_mask, audio_bus).
Per-asset via the sound’s Default Audio Bus property in the IDE.

Without one of these, the sound routes directly to the master output, bypassing your filter bus.

Fix 1: audio_play_sound_ext

var snd = audio_play_sound_ext(
    snd_splash,
    1,           // priority
    false,       // loop
    1.0,         // gain
    0,           // offset
    1.0,         // pitch
    0,           // listener mask
    audio_bus_lowpass   // bus reference
);

The sound now routes through audio_bus_lowpass and inherits its effects.

Fix 2: Per-Asset Default Bus

Open the sound asset in the IDE. Find the Audio Bus property. Set to audio_bus_lowpass. Save. Now plain audio_play_sound calls on this sound also route through the bus — no per-call argument needed.

Switching Bus at Runtime

/// On entering underwater area
for (var i = 0; i < array_length(active_sfx_emitters); i++) {
    var e = active_sfx_emitters[i];
    audio_emitter_bus(e, audio_bus_underwater);
}

For currently-playing sounds, re-route via the emitter API. New plays use the default bus (or the per-play argument).

Verify the Effect Chain

Open the AudioBus asset. Inspector shows the effect chain. Each effect has parameters — LowPass with cutoff at 22000 Hz (sample rate ceiling) is effectively bypassed. Set cutoff to 800 Hz for a noticeable muffled effect.

Diagnose with audio_bus_get_emitters

var emitters = audio_bus_get_emitters(audio_bus_lowpass);
show_debug_message("Active emitters on lowpass: " + string(array_length(emitters)));

Run during play. Empty array = no sounds routed = the bus isn’t being used. Confirms the routing layer is broken, not the effect parameters.

Verifying

Play a sound while underwater. With the bus routing fixed and the LowPass at low cutoff, the sound should be muffled. Switch to a normal area; subsequent plays route through the dry bus and sound clear.

“Effects live on buses. Sounds need to opt into the bus. Without opting in, they bypass and you hear nothing applied.”

Set Default Audio Bus on sound assets where the bus is permanent — saves per-call arguments at every play site.