Audio

DirectXTK

The DirectXTK for Audio components implement a low-level audio API similar to the XNA Game Studio 4 (Microsoft.Xna.Framework.Audio) design. This consists of the following classes all declared in the Audio.h header (in the Inc folder of the distribution):

AudioEngine - This class represents an XAudio2 audio graph, device, and mastering voice.
SoundEffect - A container class for sound resources which can be loaded from .wav files. These can be played as 'one-shots' managed by the engine, or used to create a SoundEffectInstance.
SoundEffectInstance - Provides a single playing, looped, paused, or stopped instance of a sound. These support 3D positional audio and optionally reverb effects.
SoundStreamInstance - SoundEffectInstance for playing waves from a streaming XACT-style .xwb wave bank.
DynamicSoundEffectInstance - SoundEffectInstance where the application provides the audio data on demand.
WaveBank - A container class for sound resources packaged into an XACT-style .xwb wave bank, with support for directly playing one-shots and creating SoundEffectInstances that refer to entries in the wave bank.
AudioListener, AudioEmitter - Utility classes used with SoundEffectInstance::Apply3D.

DirectXTK for Audio uses XAudio 2. It does not make use of the legacy XACT Engine, XACT Cue, or XACT SoundBank.

Related tutorials: Adding the DirectX Tool Kit for Audio, Adding audio to your project, Creating and playing sounds, Making use of wave banks, Using positional audio

Header

#include <Audio.h>

Initialization

The first step in using DirectXTK for Audio is to create the AudioEngine, which creates an XAudio2 interface, an XAudio2 mastering voice, and other global resources.

// This is only needed in Windows desktop apps
hr = CoInitializeEx( nullptr, COINIT_MULTITHREADED );
if (FAILED(hr))
    // error

...

std::unique_ptr<AudioEngine> audEngine;

...
AUDIO_ENGINE_FLAGS eflags = AudioEngine_Default;
#ifdef _DEBUG
eflags |= AudioEngine_Debug;
#endif
audEngine = std::make_unique<AudioEngine>( eflags );

Per-frame processing

The application should call Update every frame to allow for per-frame engine updates, such as one-shot voice management. This could also be done in a worker thread rather than on the main rendering thread.

if ( !audEngine->Update() )
{
    // No audio device is active
    if ( audEngine->IsCriticalError() )
    {
        ...
    }    
}

Update returns false if no audio is actually playing (either due to there being no audio device on the system at the time AudioEngine was created, or because XAudio2 encountered a Critical Error--typically due to speakers being unplugged). Calls to various DirectXTK for Audio methods can still be made in this state but no actual audio processing will take place. See AudioEngine for more information.

Loading and a playing a looping sound

Creating SoundEffectInstances allows full control over the playback, and are provided with a dedicated XAudio2 source voice. This allows control of playback, looping, volume control, panning, and pitch-shifting.

std::unique_ptr<SoundEffect> soundEffect;
soundEffect = std::make_unique<SoundEffect>( audEngine.get(), L"Sound.wav" );
auto effect = soundEffect->CreateInstance();

...

effect->Play( true );

Playing one-shots

A common way to play sounds is to trigger them in a 'fire-and-forget' mode. This is done by calling SoundEffect::Play rather than creating a SoundEffectInstance. These use XAudio2 source voices managed by AudioEngine, are cleaned up automatically when they finish playing, and can overlap in time. One-shot sounds cannot be looped or have positional 3D effects.

soundEffect = std::make_unique<SoundEffect>( audEngine.get(), L"Explosion.wav" );
soundEffect->Play();

...

soundEffect->Play();

Applying 3D audio effects to a sound

DirectXTK for Audio supports positional 3D audio with optional environmental reverb effects using X3DAudio.

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

...

soundEffect = std::make_unique<SoundEffect>( audEngine.get(), L"Sound.wav" );
auto effect = soundEffect->CreateInstance( SoundEffectInstance_Use3D
    | SoundEffectInstance_ReverbUseFilters );

...

effect->Play(true);

...

AudioListener listener;
listener.SetPosition( ... );

AudioEmitter emitter;
emitter.SetPosition( ... );

effect->Apply3D( listener, emitter );

Note: A C++ exception is thrown if you call Apply3D for a SoundEffectInstance that was not created with SoundEffectInstance_Use3D

Apply3D assumes the emitter and listener are using right-handed coordinates. You can pass 'false' for the rhcoords parameter which defaults to 'true' if using left-handed coordinates.

Using wave banks

Rather than loading individual .wav files, a more efficient method is to package them into a "wave bank". This allows for more efficient loading and memory organization. DirectXTK for Audio's WaveBank class can be used to play one-shots or to create SoundEffectInstances from 'in-memory' wave banks.

std::unique_ptr<WaveBank> wb;
wb = std::make_unique<WaveBank>( audEngine.get(), L"wavebank.xwb" ) );

A SoundEffectInstance can be created from a wavebank referencing a particular wave in the bank:

auto effect = wb->CreateInstance( 10 );
if ( !effect )
    // Error (invalid index for wave bank)

...

effect->Play( true );

One-shot sounds can also be played directly from the wave bank.

wb->Play( 2 );
wb->Play( 6 );

DirectXTK for Audio's WaveBank class can also be used to create SoundStreamInstances for streaming wave banks.

auto stream = wb->CreateStreamInstance( 10 );
if ( !stream )
    // Error (invalid index for wave bank)

...

stream->Play( true );

XACT3-style "wave banks" can be created by using the XWBTool command-line tool, or they can be authored using XACT3 in the DirectX SDK. Note that the XWBTool will not perform any format conversions or compression, so more full-featured options are better handled with the XACT3 GUI or XACTBLD, or it can be used on .wav files already compressed by adpcmencode.exe, xwmaencode.exe, xma2encode.exe, etc.

xwbtool -o wavebank.xwb Sound.wav Explosion.wav Music.wav

xwbtool -s -o streamingwb.xwb Track1.wav Track2.wav Track3.wav Track4.wav

DirectXTK for Audio does not make use of the XACT engine, nor does it make use of XACT "sound banks" .xsb or "cues". We only use .xwb wave banks as a method for packing .wav data.

Voice management

Each instance of a SoundEffectInstance will allocate it's own source voice when played, which won't be released until it is destroyed. Each time a one-shot sound is played from a SoundEffect or a WaveBank, a voice will be created or a previously used one-shot voice will be reused if possible.

See AudioEngine for more information.

Platform support

The standard DirectXTK.lib and all versions of DirectXTK12.lib include DirectXTK for Audio implemented using XAudio 2.9 which is supported by Windows 10 and Xbox built into the operating system.

DirectXTK_Desktop_2019_Win10 DirectXTK_Desktop_2017_Win10	Windows desktop applications for Windows 10
DirectXTK_Windows10_2019 DirectXTK_Windows10_2017	Universal Windows Platform (UWP) apps
DirectXTK_XboxOneXDK_2017 DirectXTK_GDK_2017 DirectXTK_GDK_2019	Xbox apps. This includes support for XMA2 format wave files.

XAudio Versions

To add DirectXTK for Audio support for a Win32 desktop application running on Windows 7 or Windows 8.x, you must add one of the following projects from the Audio folder of the distribution to your solution and Add a Reference to it (see DirectXTK for more details).

DirectXTKAudio_Desktop_2019_Win8 DirectXTKAudio_Desktop_2017_Win8	When targeting Windows 8.x or later, use `DirectXTKAudioWin8.lib` which is implemented with XAudio 2.8 included in Windows 8 or later. This version does not support xWMA wave files.
DirectXTKAudio_Desktop_2019_Win7 DirectXTKAudio_Desktop_2017_Win7	When targeting Windows 7 Service Pack 1 or later, use `DirectXTKAudioWin7.lib` which is implemented using the XAudio2 Redistribution NuGet package. This is the recommended way to support Windows 7. Using this version requires you add NuGet package Microsoft.XAudio2.Redist to your project. This version also provides xWMA support even on Windows 8.x.

The NuGet package directxtk_desktop_2017 is designed for Windows 7 compatibility for the main library, and the DirectX Tool Kit for Audio uses XAudio2Redist to support Windows 7 or later.

See the Adding the DirectX Tool Kit for Audio tutorial for a walk-through of configuring different XAudio2 Versions.

It's recommended that you use XAudio 2.9, XAudio 2.8, or the XAudio2Redist. Use of XAudio 2.7 and the legacy DirectX SDK is not recommended, and support for this configuration is removed as of the June 2020 release.

Using the vcpkg C++ library manager

The DirectX Tool Kit for Audio is also available through the vcpkg C++ Library Manager.

For Windows 7 or later support, use:

vcpkg install directxtk[xaudio2redist]

For the 64-bit version of the library, use:

vcpkg install directxtk[xaudio2redist]:x64-windows

To make use of the xaudio2redist port, you must also add to your project CMakeLists.txt:

target_compile_definitions(${PROJECT_NAME} PRIVATE USING_XAUDIO2_REDIST)
if (NOT EXISTS "${_VCPKG_INSTALLED_DIR}/${VCPKG_TARGET_TRIPLET}/include/xaudio2redist/xaudio2.h")
    message(FATAL_ERROR "VCPKG port 'xaudio2redist' required for DirectX Tool Kit for Audio on Windows 7")
endif()
target_include_directories(${PROJECT_NAME} PRIVATE ${_VCPKG_INSTALLED_DIR}/${VCPKG_TARGET_TRIPLET}/include/xaudio2redist)
target_link_directories(${PROJECT_NAME} PRIVATE ${_VCPKG_INSTALLED_DIR}/${VCPKG_TARGET_TRIPLET}/lib)
target_link_libraries(${PROJECT_NAME} PRIVATE xaudio2_9redist.lib)

For the directxtk port, there are also [xaudio2-9] and [xaudio2-8] features available.

Audio support is already included when building for any *-uwp triplet or when using the directxtk12 port.

Content Pipeline

Note: When adding .xwb files to your Universal Windows Platform app or Xbox One XDK project, you need to manually set the file properties to "Content: Yes" for all configurations to have these files included in your AppX package. .wav files are automatically detected as a media file and are included as content by default.

Statistics

Real-time data about the audio system is provided by GetStatistics.

auto stats = m_audEngine->GetStatistics();

wchar_t buff[256] = {};
swprintf_s(buff, L"Playing: %zu / %zu; Instances %zu; Voices %zu / %zu / %zu / %zu; %zu audio bytes",
    stats.playingOneShots, stats.playingInstances,
    stats.allocatedInstances, stats.allocatedVoices, stats.allocatedVoices3d,
    stats.allocatedVoicesOneShot, stats.allocatedVoicesIdle,
    stats.audioBytes);

Threading model

The DirectXTK for Audio methods assume it is always called from a single thread. This is generally either the main thread or a worker thread dedicated to audio processing. The XAudio2 engine itself makes use of lock-free mechanism to make it 'thread-safe'.

Note that IVoiceNotify::OnBufferEnd is called from XAudio2's thread, so the callback must be very fast and use thread-safe operations.