Table of Contents

Wwise SDK 2019.1.6
Integrating Listeners

Introduction

A listener is a game object that represents a microphone position in the game. Designating a game object as a listeners allows 3D sounds to be assigned to the speakers to mimic a real 3D environment. Similarly, an emitter game object represents a virtual speaker, and when assigned to a listener, the emitter’s positional information is mapped into the listener's coordinate system to render a 3D sound. Game objects in Wwise, whether acting as emitters or listeners (or both) are assigned a transform - a position vector, as well as front and top orientation vectors. Game object’s transforms must be updated on each frame to ensure that sounds are rendered through the correct speakers.

Registering a Listener

In order to hear sound, at least one game object must be registered and assigned as a listener. You may use AK::SoundEngine::SetDefaultListeners to assign a listener to all other game objects, or AK::SoundEngine::SetListeners to assign a listener to a specific game object, and override what has been set using AK::SoundEngine::SetDefaultListeners. Here is how we register a game object, and assign it as a default listener:

AkGameObjectID MY_DEFAULT_LISTENER = 0;
// Register the main listener.
AK::SoundEngine::RegisterGameObj(MY_DEFAULT_LISTENER, "My Default Listener");
// Set one listener as the default.
AK::SoundEngine::SetDefaultListeners(&MY_DEFAULT_LISTENER, 1);
// Register a game object for playing sounds
AkGameObjectID MY_EMITTER = 1;
AK::SoundEngine::RegisterGameObj(MY_EMITTER, "My Emitter");
// At this point "My Emitter" has 1 listener, "My Default Listener", because we designated it as the default listener.
AkGameObjectID MY_LISTENER_NO2 = 2;
AK::SoundEngine::RegisterGameObj(MY_LISTENER_NO2, "My Listener #2");
// If we want to change the listener for only "My Emitter", we do so as follows:
AK::SoundEngine::SetListeners(MY_EMITTER , &MY_LISTENER_NO2, 1);
// At this point, "My Emitter" has listener "My Listener #2". All other game object still have "My Default Listener" as their listener.

You may inspect the emitter-listener associations that have been assigned in code by looking at the Emitter-Listener tab of the Advanced Profiler in the Wwise authoring tool. A simple game will elect a single game object as the default listener for all game objects; however, it is possible to use multiple listeners to output to a single output device. See Multiple Listeners In A Single Output Device below. It is also possible to use listeners for 3D positioning of submixes. To do so, it is necessary to assign listeners to game object that are also listeners creating a directed graph of game objects, connected by emitter-listener associations.

Setting the Listener's Positioning Information

The AK::SoundEngine::SetPosition() function is used, like for all game objects, to set the listener's position. This should be done every time any of the listener's position or orientation vectors change.

AkTransform listenerTransform;
(... set the position and orientation members of listenerTransform here...)
AK::SoundEngine::SetPosition( listenerPosition );

The AkTransform classes hold the information that define the listener's location and orientation in the game's 3D space. The listener's location (Position), OrientationFront, and OrientationTop vectors may be accessed and set using the getters and setters of the AkTransform class.

Note: The OrientationFront vector defines the direction that the listener's head is facing. It should be orthogonal to the OrientationTop vector, which defines the incline of the listener's head. For a human listener, one could think of the OrientationFront vector as the listener's nose (going away from the face), while the OrientationTop vector would be orthogonal to it, going up from the nose, between the listener's eyes, past the forehead and beyond.

Refer to X-Y-Z Coordinate System for information regarding how the X, Y, and Z axes are defined in the Wwise sound engine.

The orientation vectors must be defined for the audio to be rendered properly. They cannot be zero vectors and need to be unit vectors. They also need to be at right angles.

Note: The listener's position is updated at most once per frame. Even if multiple calls to the AK::SoundEngine::SetPosition() function were made, only the last value will be considered when AK::SoundEngine::RenderAudio() is called.
Tip: If you are experiencing unexpected sound rendering, for example what was expected on the left speakers is actually heard on the right speakers, check the listener's positional information that is provided to the sound engine through the AK::SoundEngine::SetPosition() function. You may try to set a known constant listener's position and check that the rendering is correct in that case to rule out any mix-up in the X, Y, and Z axes. For more information about this, refer to X-Y-Z Coordinate System.

Multiple Listeners In A Single Output Device

In a single-player game where you always see only one point of view in the game, one listener is enough. However, if multiple players can play on the same system, or if multiple views are displayed at the same time, each view requires its own listener so audio is appropriately rendered for all of these views.

The main difficulty involved with implementing multiple listeners comes from the fact that the positioning of the sound sources doesn't always makes sense in relation to what players are seeing. This is mostly caused by a game using only a single set of speakers to reproduce a 3D environment for several players.

A simple representation of this problem is shown in the following figure. It is very hard to tell in which speakers the source should be played, because Listener 0 expects to hear the source in the left speaker while Listener 1 expects to hear it in the right one.

MultipleListeners_Issues_WhichSpeaker.gif
Figure: Two listeners hearing the same source in different speakers

Wwise can have any number of listeners, and by default all listeners will mix in the main output device, unless:

The following sections cover the cases where all listeners merge into the same output device, and describe how the Wwise sound engine lets the programmer manipulate these listeners to achieve the expected behavior.

Note: Everything related to multiple listeners is only available through game programmer implementation via the SDK. There are no special options in the Wwise authoring application to manage the in-game positioning of sources for multiple listeners.

Multiple Listeners: Capturing Sources

Each listener spawns a mixing graph. For each source, distance and cone attenuation are computed individually relative to each listener on which they are active.

Volume Attenuation Management

When multiple listeners capture a source, the source is mixed successively in each bus instance corresponding to its respective listener. As it is mixed, the attenuation volume is applied independently for each listener.

LPF Attenuation Management

As opposed to attenuation volume, attenuation LPF and HPF are applied directly on sources; therefore, Wwise has to choose a single value based on all emitter-listener associations for a given source. Here is how the sound engine computes the final low pass filter to apply on each source:

  1. For each listener on which this source is active:
    1. Compute the LPF based on distance between the source and this listener.
    2. Compute the LPF based on angle between the source and this listener.
    3. Keep the highest of the two values.
  2. Take the lowest value among all the listeners, and add the object's LPF (regular value and RTPC).

In the example detailed in the following table, the value for listener 0 is max( 10, 40 ) = 40, and the value for listener 1 is max( 50, 10 ) = 50. The lowest of the two is 40, which is then added to the object's value of 5 to produce the final value, 45:

Listener 0
Listener 1
Object
Final LPF for
the source
Cone LPF
Radius LPF
Cone LPF
Radius LPF
10 40 50 10 5 45

Volume Offset and Spatialization

3D Spatialization pans sounds across the various speakers based on the positions of those sounds relative to the listeners.

However, if the game is played by two players on a split screen, you might want to hear listener 1 (the first player) in the left speakers and listener 2 (the second player) in the right speakers, completely bypassing regular positioning of sounds across speakers based on their positions relative to each listener.

To give more control and flexibility, Wwise allows the game programmer to disable spatialization for a given listener and, optionally, set custom volume offsets for each channel, thus specifying how the sounds captured by this listener will be heard in each speaker.

These settings can be modified for each listener by calling AK::SoundEngine::SetListenerSpatialization():

AkGameObjectID in_uListenerID, // Listener game object ID
bool in_bSpatialized, // Spatialization toggle (True : enable spatialization, False : disable spatialization)
AkChannelConfig in_channelConfig, // Channel configuration associated with volumes in_pVolumeOffsets. Ignored if in_pVolumeOffsets is NULL.
AK::SpeakerVolumes::VectorPtr in_pVolumeOffsets = NULL // Per-speaker volume offset, in dB. See AkSpeakerVolumes.h for how to manipulate this vector.
) = 0;

The first parameter is the listener ID. The second parameter must be set to True to enable spatialization for this listener and False to disable it. Finally, the two last parameters represent a vector that contains the attenuation, in dB, for each channel on that listener. If in_bSpatialized is False, then it sets the volume for each channel, which are 0 dB by default. If in_bSpatialized is True, it offsets the volume computed by default 3D spatialization computation by a given amount for each channel.

The volume vector is tied to the channel configuration in_channelConfig. If in_channelConfig means 5.1, then the volume vector should have 6 values. Use functions defined in the AK::SpeakerVolumes::Vector namespace to manipulate it. The channel ordering corresponds to the channel mask bits defined in AkSpeakerConfig.h, except for the LFE which is always at the end.

For the example where two players use a split screen, the programmer could use the following code:

// Register listeners 1 and 2 as default listeners for all emitters.
// You may want to explicitly pick and choose which emitters emit to which listeners by using AK::SoundEngine::SetListeners instead.
AkGameObjectID listeners[2] = {1,2};
AK::SetDefaultListeners(listeners[0],2);
// Define speaker offsets using a 7.1 speaker setup (if platform supports it).
vVolumes[0] = 0.f; // Left
vVolumes[1] = -96.3f; // Right
vVolumes[2] = -6.f; // Center
vVolumes[3] = 0.f; // Rear left
vVolumes[4] = -96.3f; // Rear Right
vVolumes[5] = 0.f; // Side left
vVolumes[6] = -96.3f; // Side Right
vVolumes[7] = 0.f; // LFE
AK::SoundEngine::SetListenerSpatialization( listeners[0], false, cfg, vVolumes );
vVolumes[0] = -96.3f; // Left
vVolumes[1] = 0.f; // Right
vVolumes[2] = -6.f; // Center
vVolumes[3] = -96.3f; // Rear left
vVolumes[4] = 0.f; // Rear Right
vVolumes[5] = -96.3f; // Side left
vVolumes[6] = 0.f; // Side Right
vVolumes[7] = 0.f; // LFE
AK::SoundEngine::SetListenerSpatialization( listeners[1], false, cfg, vVolumes );

If the bus in which sounds are routed has a channel configuration other than 7.1, as per its user-defined channel configuration, the vector will be downmixed internally, using standard downmix recipes, before being applied to sounds.

To go back to regular spatialization, you would call:

// Enable regular spatialization on listeners 0 and 1

Volume Pipeline

The following figure shows, in order, the different operations performed on every source for each listener to compute the final volume in each speaker:

MultipleListeners_Spatialization.gif
Figure: Volume Pipeline in the Wwise Sound Engine
See also