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CD-XA (eXtended Architecture) audio provides compressed audio streaming for PlayStation games, allowing background music and sound effects without consuming main memory.

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What is XA Audio?

XA audio is a compressed audio format that:
  • Uses ADPCM compression (4:1 ratio compared to raw PCM)
  • Streams directly from CD during gameplay
  • Stores audio in 2336-byte Mode 2 Form 2 sectors
  • Supports stereo or mono playback at various sample rates
  • Interleaves multiple audio channels in a single file

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XA Audio in ISO Images

XA files are mixed-mode files that require special handling:
  • Each sector contains a subheader defining its format
  • Sectors are marked as Mode 2 Form 2 in the CD structure
  • mkpsxiso properly encodes each sector based on its subheader
  • Files must be in raw 2336-byte sector format

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Adding XA Audio to Your ISO

1

Prepare XA Audio Files

Ensure your XA files are properly formatted:
  • Files must be in raw 2336-byte sector format
  • Must contain valid RIFF headers
  • Each sector must have proper XA subheaders
  • Use PlayStation SDK tools or converters to create XA files
mkpsxiso will error if XA files have improperly ripped or encoded subheaders. Always verify your source files are in the correct format.
2

Add Files to XML

Define XA files in your ISO project with type="mixed":
<directory_tree>
  <dir name="audio">
    <file name="bgm01.xa" type="mixed" source="audio/bgm01.xa"/>
    <file name="bgm02.xa" type="mixed" source="audio/bgm02.xa"/>
    <file name="sfx.xa" type="mixed" source="audio/sfx_voices.xa"/>
  </dir>
</directory_tree>
You can use type="xa" as an alias for type="mixed". Both are functionally identical.
3

Consider File Placement

Place XA files strategically in your file order:
<directory_tree>
  <!-- System files -->
  <file name="system.cnf" source="system.cnf"/>
  <file name="game.exe" source="game.exe"/>
  
  <!-- Level data -->
  <dir name="levels">
    <file name="level1.dat" source="levels/level1.dat"/>
    <!-- Place XA file near level data it's used with -->
    <file name="level1.xa" type="xa" source="audio/level1.xa"/>
    
    <file name="level2.dat" source="levels/level2.dat"/>
    <file name="level2.xa" type="xa" source="audio/level2.xa"/>
  </dir>
</directory_tree>
Place XA files immediately after the game data they accompany. This minimizes seek times when the game loads a level and starts streaming music.
4

Build and Test

Build your ISO and test audio playback:
mkpsxiso myproject.xml
Test in an emulator or on hardware to verify:
  • Audio plays without stuttering
  • Correct channels play at the right times
  • No audio glitches or pops

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XA File Format Details

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Sector Structure

Each XA sector contains:
  • Subheader (8 bytes): Defines sector type and audio parameters
  • Audio Data (2324 bytes): Compressed ADPCM samples
  • EDC (4 bytes): Error detection code

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Subheader Fields

The XA subheader specifies:
  • File Number: Which file this sector belongs to
  • Channel Number: Which audio channel (for interleaving)
  • Submode: Audio format and sector flags
  • Coding Info: Sample rate, stereo/mono, bits per sample

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Form 2 Encoding

XA audio uses Mode 2 Form 2 sectors:
  • No error correction (ECC)
  • Optional error detection (EDC)
  • More space for audio data
  • Higher throughput for streaming

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EDC Configuration

Control error detection code generation: 
<track type="data" xa_edc="true">
  <!-- Files with EDC in Form 2 sectors -->
</track>
Or disable EDC for games that don’t use it: 
<track type="data" xa_edc="false">
  <!-- Files without EDC -->
</track>
If xa_edc is not specified, it defaults to true. Most PlayStation games use EDC for better reliability.

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Channel Interleaving

XA files can contain multiple interleaved audio channels: 
Sector 1: Channel 0
Sector 2: Channel 1
Sector 3: Channel 0
Sector 4: Channel 1
...
This allows:
  • Multiple music tracks in one file
  • Left/right channel separation
  • Background music + sound effects

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Creating XA Audio Files

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From PlayStation SDK

Use official tools from the PsyQ SDK: 
# Example using SDK tools
vab2xa input.vab output.xa

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Third-Party Tools

Several community tools can create XA files:
  • PSound: PlayStation sound tool
  • jPSXdec: Extract and convert XA from disc images
  • psximager: Alternative ISO creation with XA support

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Extracting from Existing Games

Use dumpsxiso to extract XA files: 
dumpsxiso -x originalgame.bin
Extracted XA files can be:
  • Used as reference for format
  • Modified with hex editors
  • Reused in your own projects

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Common XA Audio Patterns

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Background Music

<dir name="music">
  <file name="title.xa" type="xa" source="audio/title_screen.xa"/>
  <file name="stage1.xa" type="xa" source="audio/level1_bgm.xa"/>
  <file name="stage2.xa" type="xa" source="audio/level2_bgm.xa"/>
  <file name="boss.xa" type="xa" source="audio/boss_theme.xa"/>
</dir>

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Voice Acting

<dir name="voice">
  <file name="intro.xa" type="xa" source="voice/intro_speech.xa"/>
  <file name="cutscene01.xa" type="xa" source="voice/scene1_dialog.xa"/>
  <file name="cutscene02.xa" type="xa" source="voice/scene2_dialog.xa"/>
</dir>

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Interleaved Multi-Channel

<!-- Single file with multiple interleaved channels -->
<file name="sfxbank.xa" type="xa" source="audio/sfx_8channel.xa"/>

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Troubleshooting

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RIFF Header Errors

If mkpsxiso reports RIFF header errors:
  • Verify files are genuine XA format, not WAV files renamed to .xa
  • Check that files haven’t been corrupted during transfer
  • Re-export from original source

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Subheader Validation Failures

If subheader checks fail:
  • Files may be improperly ripped from a disc
  • Sectors may not have valid XA subheaders
  • Files might be in the wrong sector format
mkpsxiso performs strict XA validation. Files that work in emulators might still fail validation if they have non-standard formatting.

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Audio Stuttering or Glitches

If audio playback has issues:
  • Check file placement: Move XA files closer to related game data
  • Verify encoding: Ensure proper sample rate and format
  • Test on hardware: Emulator behavior may differ from real hardware

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Wrong Audio Playing

If the wrong audio plays:
  • Check channel numbers in subheaders
  • Verify your game code is requesting the correct file
  • Ensure file names match what the game expects

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Performance Considerations

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Streaming Reliability

For smooth playback:
  • Place frequently used XA files early on the disc
  • Group related audio files together
  • Avoid placing XA files after large data files

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Seek Time Optimization

<!-- Good: Audio near the data it's used with -->
<file name="level1.dat" source="levels/level1.dat"/>
<file name="level1_bgm.xa" type="xa" source="audio/level1.xa"/>

<!-- Bad: Audio far from related data -->
<file name="level1.dat" source="levels/level1.dat"/>
<!-- ... many other files ... -->
<file name="level1_bgm.xa" type="xa" source="audio/level1.xa"/>

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Multiple XA Files vs. Single Large File

Consider:
  • Multiple files: Easier to manage, better for selective loading
  • Single interleaved file: Better streaming performance, less seeking
Choose based on your game’s audio architecture.

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XA Audio Best Practices

Optimal XA Usage:
  • Use 37800 Hz sample rate for best quality/size ratio
  • Interleave multiple channels for efficiency
  • Place XA files strategically to minimize seek times
  • Test on actual hardware for accurate performance
  • Keep individual XA files under 10MB when possible

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Next Steps

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