Apply Room Acoustics in FMOD
The acoustics features provide spatial cues beyond the direct path HRTF, including reflections and reverb. This creates a sense of space and helps to anchor spatial audio sources into the world.
The Meta XR Audio SDK offers two different Acoustic Models:
The Shoebox Room which offers a lightweight solution with manual controls of a rectangular room. All components associated with this model are prefixed “MetaXRAudioRoom”.
Acoustic Ray Tracing which offers a more natural audio experience than the Shoebox Room solution and simplifies sound design by automating what are typically more manual processes with intuitive controls. All components associated with this model are prefixed “MetaXRAcoustic”. Acoustic Ray Tracing is implemented entirely in unity even if you are using Middleware and is
fully documented in its own section.
By the end of this document, you’ll be able to:
- Setup your project to use Meta XR Audio.
- Setup an Audio Source to be spatialized and enter the Meta XR Reflections engine.
- Select which acoustic model Meta XR Audio will use for rendering.
- Adjust the available parameters for acoustics.
- Learn about the specific technical details about every parameter for acoustics.
Place the MetaXRAudio Reflections effect before the Fader on the Master Bus channel. These parameters will affect all sounds in the project using the MetaXRAudio Source Plugin.
From the main menu, select Window > Mixer.
In the space before the Fader, right-click (Cmd+click on Mac) and select Add Effect > Plug-in Effects > Meta > MetaXRAudio Reflections.
This effect contains parameters that directly control the reverb as well as global settings that are shared across all instances of the spatializer.
IMPORTANT: The MetaXRAudio Reflections plugin is shared by all sources. This means the plugin is a singleton and only one instance of this plugin can exist in your FMOD project. If you create more than one instance of MetaXRAudio Reflections in your project, you will experience undefined behavior.
The following image shows the reverb settings for the spatializer.
| Parameter | Description |
|---|
Early Reflections Enabled | When enabled, the low order reflections of each audio object will be rendered. When disabled, no object will have it’s lower order reflections rendered. |
Reverb Enabled | This enables the late reverbation modelling for all audio objects. When disabled, no reverb will be applied. |
Reverb Level (dB) | Use this parameter to adjust the overall level of the reverb relative to it’s acoustically accurate position. A positive value increases the reverb level for all objects and is applied on top of whatever audio object reverb level is specified (see below) and a negative value decreases the reverb level for all audio objects. |
Voice Limit | When using the FMOD Studio app, use this parameter to artificially limit the maximum number of sources the reflections plugin can support to experiment with different, more efficient settings and test out your mixer bus voice limits and SFX priorities. This parameter will be used when loading the plug-in to determine how many audio objects to allocate. This means you can use this parameter to tune the CPU and memory consumption of the plugin in-game. Note this also means that if you change the parameter you must save your FMOD project, exit FMOD Studio, and then reopen the project for the change to apply. |
With the above configuration, we can start generating reflections and hearing acoustics. However, the FMOD plugin does not provide an interface to control the actual room itself (geometry, room materials, etc..). This is all controlled inside either Unity or Unreal instead, as the game engines are the location where these properties are setup.
Selecting your Acoustic Model In order to tell the Meta XR Audio SDK which of the two options to utilize, navigate to Edit > Project Settings > Meta XR Acoustics. Find the Acoustic Model dropdown and selected the desired option. Note that automatic will prefer the Raytraced Acoustics option if the project is setup to use it.
Recall that you can tell which model a component will be used for by observing the prefix of the name:
- “MetaXRAudioRoom” components adjust the Shoebox Room
- “MetaXRAcoustic” components adjust the Raytraced Acoustics
Important: If you would like to use Acoustics, proceed to
the documentation specific to that engine. If you prefer to use the lightweight Static Room engine, continue reading on this page to learn about the Room Acoustic Properties component.
Shoebox Room Acoustics Overview
The room acoustics feature provides realistic spatial early reflections and reverb for a room. This creates a sense of space and helps to anchor spatial audio sources into the world. The room dimensions and materials can be manually configured to get a response that matches your scene. If there is no Room Acoustic component in the scene, a default room will be applied.
There should only ever be one instance of the Room Acoustics component in a scene. If more than one Room Acoustics. components exist in a scene, the behavior is undefined. It doesn’t matter where the Room Acoustics component is placed in the scene hierarchy. It can simply be added to an empty GameObject.
Room Acoustics Properties Parameters The properties of the Static Room acoustics engine are controlled by the Room Acoustics Properties component. This component will determine the sound of the reflections and reverb applied to sounds. A larger room will create a longer reverb tail, and harder materials will make the room more reverberant (louder reverb).
If Lock Position To Listener, is disabled, then the position of the listener within the room will have an effect on the sound, with reflections arriving sooner from walls that a listener is closer to, and reflections arriving later from walls that are further away. This is best used in scenes that consist of a single room. If Lock Position to Listener is enabled, this keeps the room centered on the listener (camera), so the sounds of reflections are independent of the user’s position.
| Property | Description |
|---|
Lock Position To Listener | If enabled, this keeps the room model centered on the listener (camera). If disabled, then the Room Acoustics component should be positioned in the geometric center of the room in world space (usually, this is the center of the 3D mesh that represents the room). This setting is recommended to be enabled unless your scene is confined to a single room. |
Width, Height, Depth | Sets the dimensions of the room model (in meters) used to determine the early reflection and reverb. Width is the x dimension, Height is the y dimension, and Depth is the z dimension. The orientation of transform of the GameObject that this script is attached to define the orientation of the room’s coordinate system. |
Materials | Defines the amount of absorption of each wall. This is frequency dependent, some materials are more absorbent than others, some absorb more high frequencies than low frequencies. |
Clutter Factor | Represents how much clutter (i.e. furniture, people, etc.) is in the room that would dampen the response. This parameter creates diffusion and can be used to tame an overly reverberant room. A setting of 0 represents no clutter at all (an empty room), whereas a setting of 1 represents an extremely cluttered room. |
If a scene has multiple rooms, and you would like to have different acoustics in each room, the properties of the Room Acoustics component can be updated at runtime.
There should only ever be one instance of the Room Acoustics component in a scene. Updating its properties (for example, changing the width, height, and depth) will immediately change the reflections and reverberation applied to sound sources. This effectively creates the illusion of moving from one room to another.
Determining when to update the properties is left to the developer. One option is to use invisible colliders placed in different parts of a scene that trigger a change in the properties when a player enters them.
Material Reflection Coefficients The following table shows the reflection coefficients for each material for each frequency band.
| Material | 0-176 Hz | 176-775 Hz | 775-3408 Hz | 3408-22050 Hz |
|---|
AcousticTile | 0.488168418 | 0.361475229 | 0.339595377 | 0.498946249 |
Brick | 0.975468814 | 0.972064495 | 0.949180186 | 0.930105388 |
BrickPainted | 0.975710571 | 0.98332417 | 0.978116691 | 0.970052719 |
Cardboard | 0.590000 | 0.435728 | 0.251650 | 0.208000f |
Carpet | 0.987633705 | 0.905486643 | 0.583110571 | 0.351053834 |
CarpetHeavy | 0.977633715 | 0.859082878 | 0.526479602 | 0.370790422 |
CarpetHeavyPadded | 0.910534739 | 0.530433178 | 0.29405582 | 0.270105422 |
CeramicTile | 0.99000001 | 0.99000001 | 0.982753932 | 0.980000019 |
Concrete | 0.99000001 | 0.98332417 | 0.980000019 | 0.980000019 |
ConcreteRough | 0.989408433 | 0.964494646 | 0.922127008 | 0.900105357 |
ConcreteBlock | 0.635267377 | 0.65223068 | 0.671053469 | 0.789051592 |
ConcreteBlockPainted | 0.902957916 | 0.940235913 | 0.917584062 | 0.919947326 |
Curtain | 0.686494231 | 0.545859993 | 0.310078561 | 0.399473131 |
Foliage | 0.518259346 | 0.503568292 | 0.5786888 | 0.690210819 |
Glass | 0.655915797 | 0.800631821 | 0.918839693 | 0.92348814 |
GlassHeavy | 0.827098966 | 0.950222731 | 0.97460413 | 0.980000019 |
Grass | 0.881126285 | 0.507170796 | 0.131893098 | 0.0103688836 |
Gravel | 0.729294717 | 0.373122454 | 0.25531745 | 0.200263441 |
GypsumBoard | 0.721240044 | 0.927690148 | 0.93430227 | 0.910105407 |
Marble | 0.990000 | 0.990000 | 0.982754f | 0.980000f |
Mud | 0.844084 | 0.726577 | 0.794683 | 0.849737 |
PlasterOnBrick | 0.975696504 | 0.979106009 | 0.961063504 | 0.950052679 |
PlasterOnConcreteBlock | 0.881774724 | 0.924773932 | 0.951497555 | 0.959947288 |
Rubber | 0.950000 | 0.916621 | 0.936230 | 0.950000 |
Soil | 0.844084203 | 0.634624243 | 0.416662872 | 0.400000036 |
SoundProof | 0.0 | 0.0 | 0.0 | 0.0 |
Snow | 0.532252669 | 0.15453577 | 0.0509644151 | 0.0500000119 |
Steel | 0.793111682 | 0.840140402 | 0.925591767 | 0.979736567 |
Stone | 0.980000 | 0.978740 | 0.955701 | 0.950000 |
Vent | 0.847042 | 0.620450 | 0.702170 | 0.799473 |
Water | 0.970588267 | 0.971753478 | 0.978309572 | 0.970052719 |
WoodThin | 0.592423141 | 0.858273327 | 0.917242289 | 0.939999998 |
WoodThick | 0.812957883 | 0.895329595 | 0.941304684 | 0.949947298 |
WoodFloor | 0.852366328 | 0.898992121 | 0.934784114 | 0.930052698 |
WoodOnConcrete | 0.959999979 | 0.941232264 | 0.937923789 | 0.930052698 |
When using early reflections, be sure to set non-cubical room dimensions. A perfectly cubical room may create reinforcing echoes that can cause sounds to be poorly spatialized. The room size should roughly match the size of the room in the game so the audio reinforces the visuals. The shoebox model works best when simulating rooms. For large spaces and outdoor areas, it should be complimented with a separate reverb.
Make sure that your Project Output Format is set to stereo. You can access this option on the menu by following Edit > Project Settings > Audio > Default Speaker Mode > Stereo.
- Learn more about advanced Acoustic Ray Tracing to use in place of the Shoebox Room model by clicking here.
- Learn about how to render ambisonic audio with the Meta XR Audio SDK by clicking here.
