Change sounds with parameters.

A parameter is a value the graph can read. Footstep uses Surface to choose grass, stone, or wood. Campfire uses Intensity to change the crackle’s volume. The graph defines what each value means.

Choose the right type

Type	Use it for	Example from the supplied graphs
Float	A number with a fractional part.	Campfire Intensity: 0.35f. The f marks a C# float.
Int	A whole number, often a choice.	Footstep Surface: 0 grass, 1 stone, 2 wood.
Bool	A yes/no choice: true or false.	LaunchSequence ClampsOpen.
Asset	An AudioClip chosen from the graph’s allowed list.	Jukebox Track.

Use the type declared in the graph. Passing 1f to an Int parameter is not the same as passing 1. A wrong type or unknown parameter is rejected. Valid numeric values are clamped to the declared range. Float values must be finite; asset values must belong to the graph’s allowed clip list.

Supply the value before the graph starts

The following is an excerpt for a method on your own footstep component. It needs the registered Footstep event, generated keys, and a Vector3 footPosition containing the contact position.

One stone footstep · excerpt

var context = SoundPlayContext.At(footPosition)
    .With(SoundParameters.Footstep.Surface, 1);
var result = SoundBus.Play(Sounds.Footstep, context);

A context is the set of choices for this play: where it happens, what it follows, and its starting parameter values. The initial Surface value is applied before On Start, so the graph selects stone on its first decision. Setting the value after Play is too late for a branch that already ran.

The Footstep demo’s gameplay surface enum uses different numbers: Unknown 0, Grass 1, Stone 2, Wood 3. Map that enum to the graph’s 0/1/2 choices; do not cast it directly.

Keep the context returned by With

With returns a changed copy of the context. Chain it as above, or assign the result:

Keep the added value · excerpt

context = context.With(SoundParameters.Footstep.Surface, 2);

Calling context.With(...) on its own and discarding the returned copy does not change context. Each call adds one entry, even if it names a parameter already added. A fifth With call throws InvalidOperationException.

More than four starting values

Use TypedParameters for a larger list. This excerpt shows the format with two values from Engine; add more only when the event actually declares them. The public typed-array constructor accepts the parameter name.

An array of initial values · excerpt

var context = SoundPlayContext.At(transform.position);
context.TypedParameters = new[]
{
    new SoundParameterOverride("Rpm", SoundValue.Float(0.4f)),
    new SoundParameterOverride("Load", SoundValue.Float(0.2f))
};
var result = SoundBus.Play(Sounds.Engine, context);

This belongs in a component method with Engine registered. Creating an array uses managed memory; reuse an array when it suits your code. The service reads its values during the call and does not keep the array, even if the play is queued. Changing that array later will not change the play.

If the same parameter is supplied more than once, the last applied value wins. The order is: graph defaults → context Parameters float array → TypedParameters array → With entries → the additional float span on the service’s TryPlay overload. Every supplied entry must still be valid; a later good value does not rescue an earlier wrong type.

Change a running sound

Keep the returned handle when a play is accepted. Then update it instead of starting the event again. Here fire is the saved Campfire handle:

Change crackle intensity · excerpt

bool changed = SoundBus.SetFloat(
    fire, SoundParameters.Campfire.Intensity, 0.35f);

changed is false if there is no suitable play, the parameter is missing, or the value is refused. For a non-float type, use SetParameter with SoundValue.Int, .Bool, or .Asset. Updating a clip parameter changes the value the graph will read; it does not by itself restart an already playing voice with the new clip.

Why the value may change gradually

A Float parameter can have a rise rate and fall rate, measured in value units per second. These make it move smoothly toward the requested value. Campfire’s rates are 0.5: moving from 0.65 to 0.35 takes about 0.6 seconds of unpaused graph time.

An initial value is applied immediately before On Start. Later Float changes use smoothing when the relevant rate is positive. A zero rate changes immediately. Int, Bool, and Asset changes do not use Float smoothing.

To inspect this in code, use the active service’s TryGetParameter. Its Current is what the graph reads now; Target is what you requested. The parameter reference lists the exact types and methods.