Using positional audio

This lesson covers the playing sounds with DirectX Tool Kit for Audio using 3D positional audio effects.

Setup

First create a new project. For this lesson, use the DeviceResources variant described in Using DeviceResources, then use the instructions in Adding the DirectX Tool Kit, then Adding the DirectX Tool Kit for Audio, and finally Adding audio to your project which we will use for this lesson.

Background

Games provide an immersive visual and audio experience, and often use 3D audio effects to enhance the audio. The effect modifies the speaker position, pitch, and volume of a sound to provide audial cues to place it in the 3D environment. XAudio2 itself provides the ability to specify a complex per-channel volume mapping, pitch modification, and other parameters to generate these 3D effects, but does not perform the computations. The X3DAudio library is used by DirectX Tool Kit for Audio to compute the virtual placement of the sound.

See Microsoft Docs for more information on X3DAudio.

Sound

Save the this file to your new project's folder: heli.wav. Use the top menu and select Project / Add Existing Item.... Select the heli.wav file and hit "OK".

In the Game.h file, add the following variables to the bottom of the Game class's private declarations:

std::unique_ptr<DirectX::SoundEffect> m_soundEffect;

In Game.cpp, add to the end of Initialize:

m_soundEffect = std::make_unique<SoundEffect>( m_audEngine.get(), L"heli.wav" );

Build and run. No sounds will be heard, but the audio file is loaded.

Troubleshooting: If you get a runtime exception, then you may have the .wav file in the wrong folder, have modified the "Working Directory" in the "Debugging" configuration settings, or otherwise changed the expected paths at runtime of the application. You should set a break-point on std::make_unique<SoundEffect> and step into the code to find the exact problem.

Play the sound

As we did in the Creating and playing sounds tutorial, we create an instance of our sound and start it looping. To ensure it reacts properly to "lost device" scenarios, we update it in a few places.

In the Game.h file, add the following variables to the bottom of the Game class's private declarations:

std::unique_ptr<DirectX::SoundEffectInstance> m_soundSource;

In Game.cpp, add to the end of Initialize:

m_soundSource = m_soundEffect->CreateInstance();
m_soundSource->Play(true);

In Game.cpp, modify the handling of m_retryAudio in Update as follows:

...
if (m_retryAudio)
{
    m_retryAudio = false;

    if (m_audEngine->Reset())
    {
        // TODO: restart any looped sounds here
        if (  m_soundSource )
             m_soundSource->Play(true);
    }
}
...

In Game.cpp, modify the destructor:

Game::~Game()
{
    if (m_audEngine)
    {
        m_audEngine->Suspend();
    }

     m_soundSource.reset();
}

Build and run to hear the helicopter sound, which at the moment will be a bit too lound.

Adding a simple scene

While not strictly required, the 3D audio effect illusion makes more sense with some visuals to go with it, so here we'll add a simple sphere.

In the Game.h file, add the following variables to the bottom of the Game class's private declarations:

std::unique_ptr<DirectX::GeometricPrimitive> m_ball;
DirectX::SimpleMath::Matrix m_proj;
DirectX::SimpleMath::Matrix m_view;
DirectX::SimpleMath::Vector3 m_position;

In Game.cpp file, modify the Game constructor to initialize our position variable:

Game::Game() noexcept(false) :
    m_position(0, 0, -10.f)
{
    m_deviceResources = std::make_unique<DX::DeviceResources>();
    m_deviceResources->RegisterDeviceNotify(this);
}

In Game.cpp, add to the TODO of CreateDeviceDependentResources:

auto context = m_deviceResources->GetD3DDeviceContext();
m_ball = GeometricPrimitive::CreateSphere(context);

In Game.cpp, add to the TODO of CreateWindowSizeDependentResources:

auto size = m_deviceResources->GetOutputSize();
m_proj = Matrix::CreatePerspectiveFieldOfView(XM_PI / 4.f,
    float(size.right) / float(size.bottom), 0.1f, 20.f);

m_view = Matrix::CreateLookAt(Vector3::Zero,
    Vector3::Forward, Vector3::Up);

In Game.cpp, add to the TODO of OnDeviceLost:

m_ball.reset();

In Game.cpp, add to the TODO of Render:

XMMATRIX world = XMMatrixTranslation(m_position.x, m_position.y, m_position.z);
m_ball->Draw(world, m_view, m_proj, Colors::Yellow);

Build and run, and you should get the following screen:

Screenshot of yellow ball

If using DirectX 12, you will also need a BasicEffect and CommonStates to render this scene. See the 3D Shapes tutorial for more details.

Applying a 3D positional effect

Now we have our sound and a visual cue where to expect the sound from, we now add the 3D audio effect processing.

In the Game.h file, add the following variables to the bottom of the Game class's private declarations:

DirectX::AudioListener m_listener;
DirectX::AudioEmitter  m_emitter;

Modify Initialize in Game.cpp so we enable 3D positioning for our instance. The AudioListener defaults the same position and view direction as our camera, so we don't have to add any explicit initialization.

m_soundSource = m_soundEffect->CreateInstance(SoundEffectInstance_Use3D);
m_soundSource->Play(true);

In Game.cpp, add to the TODO of Update:

m_emitter.Update(m_position, Vector3::Up, static_cast<float>(timer.GetElapsedSeconds()));
if (m_soundSource)
{
    m_soundSource->Apply3D(m_listener, m_emitter);
}

Build and run. The change won't be extreme, but the helicopter sounds will have a slightly lower volume.

Now, the final part of this is to add movement to the sound source. In Game.cpp, add to the TODO of Update before the call to AudioEmitter::Update:

// Move the object around in a circle.
double speed = timer.GetTotalSeconds() / 2;
m_position = Vector3(
    static_cast<float>(cos(speed)) * 5.f,
    0,
    static_cast<float>(sin(speed))) * -5.f;

Build and run, and the sound will move from left-to-right in front, then right-to-left behind. You'll only see the sphere while in front.

Technical note

We do the audio engine processing and 3D audio computations in Update for simplicity, but if StepTimer were set for for fixed-update timesteps instead of variable-rate, then you may be getting more than one call to Update per render frame. In that case, it is better to move the "audio rendering" up into Tick so it only happens once per render frame.

Environmental effects

Now that we have the basics of the effect running, it's time to turn additional features including an environmental reverb effect.

At the top of Game.cpp after the using statements, add:

namespace
{
    constexpr X3DAUDIO_CONE c_listenerCone = {
        X3DAUDIO_PI * 5.0f / 6.0f, X3DAUDIO_PI * 11.0f / 6.0f, 1.0f, 0.75f, 0.0f, 0.25f, 0.708f, 1.0f
    };
    constexpr X3DAUDIO_CONE c_emitterCone = {
        0.f, 0.f, 0.f, 1.f, 0.f, 1.f, 0.f, 1.f
    };

    constexpr X3DAUDIO_DISTANCE_CURVE_POINT c_emitter_LFE_CurvePoints[3] = {
        { 0.0f, 1.0f }, { 0.25f, 0.0f}, { 1.0f, 0.0f }
    };
    constexpr X3DAUDIO_DISTANCE_CURVE c_emitter_LFE_Curve = {
        const_cast<X3DAUDIO_DISTANCE_CURVE_POINT*>(&c_emitter_LFE_CurvePoints[0]), 3
    };

    constexpr X3DAUDIO_DISTANCE_CURVE_POINT c_emitter_Reverb_CurvePoints[3] = {
        { 0.0f, 0.5f}, { 0.75f, 1.0f }, { 1.0f, 0.0f }
    };
    constexpr X3DAUDIO_DISTANCE_CURVE c_emitter_Reverb_Curve = {
        const_cast<X3DAUDIO_DISTANCE_CURVE_POINT*>(&c_emitter_Reverb_CurvePoints[0]), 3
    };
}

Modify Initialize in Game.cpp both the audio engine creation:

    AUDIO_ENGINE_FLAGS eflags = AudioEngine_EnvironmentalReverb | AudioEngine_ReverbUseFilters;
#ifdef _DEBUG
    eflags |= AudioEngine_Debug;
#endif
    m_audEngine = std::make_unique<AudioEngine>(eflags);

    m_audEngine->SetReverb(Reverb_Hangar);

and the sound effect instance creation:

m_soundSource = m_soundEffect->CreateInstance(SoundEffectInstance_Use3D | SoundEffectInstance_ReverbUseFilters);
m_soundSource->Play(true);

m_listener.pCone = const_cast<X3DAUDIO_CONE*>(&c_listenerCone);

m_emitter.pLFECurve = const_cast<X3DAUDIO_DISTANCE_CURVE*>(&c_emitter_LFE_Curve);
m_emitter.pReverbCurve = const_cast<X3DAUDIO_DISTANCE_CURVE*>(&c_emitter_Reverb_Curve);
m_emitter.CurveDistanceScaler = 14.f;
m_emitter.pCone = const_cast<X3DAUDIO_CONE*>(&c_emitterCone);

Build and run, and now you'll hear some reverb effects as the helicopter sound passes you by.

Try setting the reverb to different presets and see how it impacts the sound. This includes the full Interactive 3D Audio Rendering Guidelines Level 2.0 set.

You may want to add AudioEngine_UseMasteringLimiter to your audio engine flags to avoid potential problems with sounds clipping if they compute to an unusually large volume level.