XACT Overview

Microsoft Cross-Platform Audio Creation Tool (XACT) provides a high level framework and tools for integrating audio resources into games. Audio designers typically use a commercially available linear audio editing package to develop the core audio elements—waves—for a game. After the waves are developed, designers can use XACT GUI or command line tool to package audio resources. Game developers can use the XACT API to integrate the packaged audio resources into the game.

XACT consists of the following components.

XACT API
Allows the integration of XACT audio resources into a game and provides methods for loading, playing and manipulating those resources. Developers will mainly interact with this part of XACT.
XACT GUI
Provides a graphical tool for packaging audio resources for use with the XACT API. Audio designers will mainly interact with this part of XACT.
XACT Command Line Tool
Provides a command line interface to the XACT audio packaging capabilities. The command line tool allows XACT to be integrated into a game's build process.

XACT Features

XACT has a comprehensive set of features for audio designers and audio developers. The following sections list some of the key features provided by XACT.

For Audio Designers
For Game Developers

For Audio Designers

The XACT authoring tool allows the designer to group waves into cues and sequences. Volume and pitch levels can also be set.

The key features of XACT include the following:

Saving to Different Audio File Formats
Supporting Speaker Channels
Organizing Sound Assets
Auditioning Sounds

Saving to Different Audio File Formats

XACT supports a variety of audio file formats, including:

WAV — The standard audio file format for Microsoft Windows environments.
AIFF — The standard audio file format for Apple Macintosh environments.
ADPCM — compressed form of Pulse Code Modulation (PCM) data.
Note ADPCM is currently only available for Windows, including XNA Game Studio Express Windows deployments.
XMA — a file format based on Microsoft Windows Media Audio (WMA).
Note XMA is currently only available for Xbox 360, including XNA Game Studio Express Xbox 360 deployments.
xWMA — xWMA is a subset of the Microsoft Windows Media Audio (WMA) compression format. xWMA uses the WMA bit-stream format in a lightweight wrapper and provides a greater compression ratio than XMA. xWMA is very useful for dialogue and music where a small CPU hit is affordable in order to achieve greater compression.

XACT supports both 16-bit and 8-bit PCM data.

XACT recognizes and properly acts on loop points that are embedded in WAV and AIFF files. This means that XACT honors loop markers that are created by using commercially available linear audio design tools.

Supporting Speaker Channels

XACT supports stereo and 5.1 channel speaker arrangements. Currently no other speaker arrangements are supported.

XACT supports multichannel audio on any machine that can play multichannel audio. A hardware accelerator card is not required to support multichannel playback.

Organizing Sound Assets

XACT provides the following ways to bundle and sequence audio elements.

Wave banks allow you to package multiple audio files into a single file. Wave bank files are identified by the .XWB extension.

This feature simplifies management of audio data. Rather than managing many audio files, titles can load a more manageable set of wave banks that bundle the waves for a section of the game.

XACT wave banks can also compress wave files to Microsoft ADPCM or XMA format.

Wave bank files can also be used by titles without the XACT engine, as a way of bundling and compressing wave assets. The format of a wave bank file is documented in the header file xact2wb.h, which can be used to create code that can parse the wave bank data.
Sound banks allow you to package cues, waves, and settings for playback by a title. Sound bank files are identified by the .XSB extension. The binary format of sound bank files is not documented.

Auditioning Sounds

XACT provides the following ways to preview audio content on the Xbox 360 and Windows.

The Audio Console application runs on Xbox 360 and Windows. It allows you to audition sound resources before using the sounds in a title. This allows audio designers to begin auditioning with XACT right away.
XACT allows you to audition sound resources in-game. If a title is built by using special development-only libraries, you can adjust the audio settings while the title is running. This allows you to test sound resources under conditions of actual gameplay.

For Game Developers

The XACTAPI functions allow you to efficiently integrate the designer's work into the title.

The XACT run-time libraries can help with the following tasks:

They can ease integration of wave, sound, and cue information that is received from the audio designer.
They can support in-memory and streaming wave banks with minimal additional work.
They can free the developer to focus on gameplay, rather than on audio hardware.
They can allow audio resources to be invoked by cue name, rather than by specific components.
They can provide notification of audio events to the title.
They can solve the problem of fitting waves within allocated memory, by providing zero-latency streaming. This feature is discussed in more detail in XACT Streaming.