Creating Audio Zones and Dynamic Mixing with Snapshots

Wed, 12 Jun 2024 00:00:00 +0000

In our previous tutorial, we mastered Playback States to control when sounds play. Now, we’re going to control how they sound based on the game environment.

Have you ever noticed how audio changes when a character walks into a cave (reverb kicks in) or when they are low on health (the sound gets muffled and bass-heavy)? In FMOD, these dynamic mixing changes are handled by Snapshots.

In this guide, we will cover:

What Snapshots are and how to create them.
Creating a Reverb Zone using Triggers.
Handling signal routing (so your UI clicks don’t echo!).
Creating a “Low Health” filter using Parameters.

What is a Snapshot?

Think of a Snapshot as a “preset” for your FMOD Mixer. When active, a Snapshot can change the volume of buses, toggle effects on and off, or change effect parameters.

There are two main types:

Overriding: Forces values to a specific state (good for absolute changes).
Blending: Adds changes on top of existing values (good for layering).

For this tutorial, we will focus on Overriding snapshots to create distinct audio zones.

Part 1: The Reverb Zone (Trigger-Based)

Let’s create a system where entering a tunnel applies reverb to our sound effects.

Step 1: FMOD Setup

Go to the Mixer window in FMOD.
Create a Return Bus for Reverb if you haven’t already, and add a Reverb effect to it.
Go to the Snapshots tab and create a new Overriding Snapshot named “Reverb Zone 1”.
Deselect your snapshot for the time being.
Select the SFX Bus and add a Send to the Reverb Return Bus. Set the send level to around -6dB (adjust to taste).
Scoping: When you select the snapshot, your mixer faders will turn into yellow outlines. This means they are “scoped out” (unaffected).
1. Select the snapshot again. Mixer controls will appear with yellow outlines, meaning they are currently scoped out.
2. Click the reverb send level on the SFX Bus so it becomes fully yellow, indicating it is scoped in and will be driven by the snapshot.
When you select the snapshot, the reverb send will be set to the value defined in the snapshot.
Modulation: To make the reverb fade in smoothly, right-click the Snapshot’s Intensity dial (in the deck area) and add an AHDSR Modulator. This ensures the reverb doesn’t snap on/off instantly.

Step 2: The Unity Script

Open Level 2 in Unity. This scene has more tunnels that we can use for testing reverb.

In Unity, Snapshots are treated almost exactly like Events. We create an instance, play it, and stop it.

Create a cube object with Create > 3D Object > Cube. Scale it to form a tunnel entrance and set its position so the player can walk through it. Make sure to set the cube’s collider to Is Trigger. Call it Reverb Zone. Also make sure the layer is set to Environment.

We’ll leave the Mesh Renderer on so you can see the zone in the scene, but in a real game, you would likely turn this off.

Create a script called F_ReverbZone and attach it to the Reverb Zone object.

using UnityEngine;
using FMODUnity;
using FMOD.Studio;

public class ReverbZone : MonoBehaviour
{
 private EventInstance reverbSnapshot;

 void Start()
 {
 // Create the instance just like a normal event
 // Note: The path starts with "snapshot:/"
 reverbSnapshot = RuntimeManager.CreateInstance("snapshot:/Reverb Zone");
 }

 void OnTriggerEnter(Collider other)
 {
 if (other.CompareTag("Player"))
 {
 reverbSnapshot.start();
 }
 }

 void OnTriggerExit(Collider other)
 {
 if (other.CompareTag("Player"))
 {
 // Allow the AHDSR to fade it out naturally
 reverbSnapshot.stop(STOP_MODE.ALLOWFADEOUT);
 }
 }

 void OnDestroy()
 {
 reverbSnapshot.release();
 }
}

Step 3: Fixing the Signal Path (The UI Echo Problem)

If you test the game now, entering the zone will reverb everything sent to the SFX bus—including your UI menu clicks! That’s not what we want. We need to split the signal.

In the FMOD Mixer:

Delete the send that goes from the SFX bus to the Reverb bus.
Create two new Group Buses under your main SFX bus: call them In-Game and UI.
Route your footsteps, attacks, and environmental sounds into In-Game.
Route your menu sounds into UI.
Place the Reverb Send on the In-Game bus only.

Now, your UI remains crisp and dry, while the game world echoes around you.

Part 2: The Distance-Based Zone (Automation)

Sometimes you don’t want a hard trigger; you want the effect to get stronger as you get closer to a specific object.

FMOD Setup

Create a new snapshot (e.g., “Reverb Zone 2”).
Instead of an AHDSR on the Intensity dial, right-click and Add Automation.
Select the built-in Distance parameter.
Draw a curve:
- At 5 meters, Intensity = 100%
- At 10 meters, Intensity = 0%

Unity Script

Since this relies on distance, we must tell FMOD where the snapshot is located in 3D space.

Create an Empty GameObject called Reverb Zone 2 and position at (-1, -3, 28.5). Create a new script and attach to the gameObject:

void Start()
{
 reverbSnapshot = RuntimeManager.CreateInstance("snapshot:/Reverb Zone 2");
 reverbSnapshot.start(); // Start immediately

 // Attach the instance to this object so FMOD knows its location
 RuntimeManager.AttachInstanceToGameObject(reverbSnapshot, transform, GetComponent<Rigidbody>());
}

void OnDestroy()
{
 reverbSnapshot.stop(STOP_MODE.IMMEDIATE);
 reverbSnapshot.release();
}

Part 3: The “Low Health” Filter (Parameter Control)

A common game mechanic is muffling audio when the player is dying. We can achieve this by controlling a Snapshot via a script parameter.

Step 1: FMOD Setup

Add a 3-EQ Effect to your In-Game bus.
Create a Snapshot called “Low Health”.
Scope in the High and Mid bands of the EQ and turn them all the way down (leaving only low frequencies).
Right-click the Snapshot’s Intensity dial and select Expose as Parameter.
Set the range of the parameter from 1 to 5.
Invert the curve:
- When Parameter = 5 (Full Health), Intensity = 0% (No filter).
- When Parameter = 1 (Low Health), Intensity = 100% (Fully muffled).

Step 2: Linking Health to Audio

In your Player Controller script, you need to update the snapshot whenever health changes.

FMOD.Studio.EventInstance healthFilter;

void Start()
{
 healthFilter = RuntimeManager.CreateInstance("snapshot:/Low Health");
 healthFilter.start();
 healthFilter.release(); // Release immediately so it cleans up when stopped
}

// Call this function whenever the player takes damage or heals
public void SetHealthSnapshot() {
 healthFilter.setParameterByName("Intensity", m_Damageable.currentHitPoints); // currentHealth should be between 1 and 5
}
void OnDestroy()
{
 healthFilter.stop(STOP_MODE.IMMEDIATE);
}

By hooking the UpdateAudioHealth function into your existing damage logic (using Unity Events or direct method calls), your audio will dynamically react to the player’s survival status.

Summary

Snapshots are powerful tools that move beyond simple “Play/Stop” commands. By treating them as Event Instances in code, you can:

Trigger reverb zones using Colliders.
Automate audio changes based on 3D Distance.
Drive mix changes using gameplay variables like Player Health.

With these tools, you’ve now covered the core pillars of FMOD implementation: Events, Parameters, Playback States, and Snapshots.

Snapshots on DAD 424 Sound Design for Games

Creating Audio Zones and Dynamic Mixing with Snapshots

What is a Snapshot?

Part 1: The Reverb Zone (Trigger-Based)

Step 1: FMOD Setup

Step 2: The Unity Script

Step 3: Fixing the Signal Path (The UI Echo Problem)

Part 2: The Distance-Based Zone (Automation)

FMOD Setup

Unity Script

Part 3: The “Low Health” Filter (Parameter Control)

Step 1: FMOD Setup

Step 2: Linking Health to Audio

Summary