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AUPRESET_FORMAT.md

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Logic Pro .aupreset File Format

Overview

AU Preset (.aupreset) files are Apple's standard format for storing Audio Unit preset data in Logic Pro. They use Apple's Property List (plist) format to store preset metadata and binary parameter data.

Format Structure

AU Preset files are XML or binary plist files containing:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>data</key>
    <data>
        [Base64-encoded binary preset data]
    </data>
    <key>manufacturer</key>
    <integer>[Manufacturer code]</integer>
    <key>name</key>
    <string>[Preset name]</string>
    <key>subtype</key>
    <integer>[AU subtype code]</integer>
    <key>type</key>
    <integer>[AU type code]</integer>
    <key>version</key>
    <integer>[Version number]</integer>
</dict>
</plist>

Key Components

1. Plist Container

  • Format: XML or binary plist
  • Root: Dictionary containing preset metadata and data
  • Encoding: UTF-8 for XML, binary for compressed storage

2. Core Metadata Fields

  • name: Preset display name (e.g., "Heavy Compression")
  • data: Base64-encoded binary preset parameters
  • manufacturer: 4-byte manufacturer code (e.g., Apple = 'appl')
  • subtype: 4-byte AU subtype identifier
  • type: 4-byte AU type identifier (e.g., Effect = 'aufx', Instrument = 'aumu')
  • version: Preset format version

3. Embedded Binary Data

The data field contains base64-encoded binary data that may include:

  • AU Parameter Values: Float values for plugin controls
  • Preset State: Complete plugin state information
  • Additional Metadata: Plugin-specific configuration data

Characteristics

  • Cross-Platform: Standard macOS/iOS plist format
  • Human Readable: XML variant allows text inspection
  • Compressed: Binary variant for smaller file sizes
  • AU Standard: Compatible with all Audio Unit plugins
  • Round-trip Safe: Preserves exact binary data for compatibility

Examples

Compressor Preset (kHs Compactor.aupreset)

<dict>
    <key>data</key>
    <data>[Base64-encoded compressor settings]</data>
    <key>manufacturer</key>
    <integer>1634758764</integer>  <!-- 'kHs ' -->
    <key>name</key>
    <string>Heavy Compression</string>
    <key>subtype</key>
    <integer>1684238189</integer>  <!-- 'Comp' -->
    <key>type</key>
    <integer>1635083896</integer>  <!-- 'aufx' (effect) -->
    <key>version</key>
    <integer>1</integer>
</dict>

File Extension

  • .aupreset: Standard Logic Pro preset file extension
  • Location: ~/Music/Audio Music Apps/Channel Strip Settings/ (within CST files), or ~/Library/Audio/Presets/ (AU system-level presets)

Relationship to Other Formats

  • Channel Strip: CST files may reference AU presets
  • Patch Bundles: Patches contain .cst files, which in turn may reference AU presets — a .patch never contains an .aupreset directly

Implementation

See Aupreset.swift for the Swift implementation that parses and serializes AU Preset files.