What Is .aup

Content on WhatAnswers is provided "as is" for informational purposes. While we strive for accuracy, we make no guarantees. Content is AI-assisted and should not be used as professional advice.

Last updated: April 10, 2026

Quick Answer: .aup is the native project file format used by Audacity, a free and open-source audio editor founded in 1999, which stores project metadata in XML format alongside separate audio data folders. The format served as Audacity's default until version 3.4.0 (released September 2023) introduced the newer .aup3 SQLite-based format, though .aup projects remain widely used and supported.

Key Facts

Audacity has received over 230 million downloads as of 2023, making .aup one of the world's most prevalent audio project formats
.aup files are XML-based plain-text files that store metadata and references to audio data stored separately in _data folders, not the audio itself
Audacity 3.4.0 introduced .aup3 format in September 2023, consolidating project data into a single SQLite database file for improved portability
.aup projects preserve non-destructive edits (volume, effects, fades) without modifying original audio until export to MP3, WAV, FLAC, or OGG formats
Unlike modern DAW formats, .aup requires both the project file and accompanying _data folder to function, making it less portable than self-contained formats

Overview

.aup is the native project file format used by Audacity, a free and open-source digital audio editor and recording software available across Windows, macOS, and Linux platforms. The file format has been the standard for Audacity projects since the software's inception in 1999, making it one of the most widely-used audio project formats for amateur and professional audio editors worldwide.

The .aup format is an XML-based text file that functions as a project container, storing metadata about audio tracks, effects, edits, and arrangement information rather than the actual audio data itself. This design separates the project file from audio data stored in an accompanying _data folder, a structural approach that remained Audacity's default until the release of version 3.4.0 in September 2023, which introduced the newer .aup3 SQLite-based format.

How It Works

.aup files operate on a specific structural principle that distinguishes them from modern audio project formats:

XML-Based Metadata Storage: .aup files contain plain-text XML code that documents all project properties including sample rate (typically 44.1 kHz or 48 kHz), track count, effect chains, zoom levels, and selection information. This makes .aup files human-readable and editable with any text editor, though this is rarely recommended.
Separate Audio Data Folders: When you save a project as .aup, Audacity automatically creates a companion folder (usually named [ProjectName]_data) containing the actual audio recordings in AU format (Audacity's native uncompressed format). The .aup file references these audio files through file paths defined in its XML structure.
Non-Portable by Default: Unlike self-contained project files, .aup projects require both the .aup file and its corresponding _data folder to function properly. Moving or renaming either component can break the project, as Audacity may lose track of referenced audio files. This structural limitation has been a notable pain point for users managing multiple projects or sharing projects across devices.
Edit Preservation Without Re-encoding: The .aup format preserves all non-destructive edits—such as volume adjustments, fade effects, and track reordering—without modifying the original audio data. Only when exporting to formats like MP3, WAV, FLAC, or OGG does Audacity process these edits and write new audio files.
Backward Compatibility: Older versions of Audacity (prior to 3.4.0) exclusively used .aup format, meaning projects created in Audacity 1.2 or 2.x could still be opened in later versions, though this compatibility sometimes required format migration.

Key Comparisons

Aspect	.aup Format	.aup3 Format	Other DAW Formats
File Structure	XML text file + separate _data folder	Single SQLite database file	Varies: .flp (FL Studio), .als (Ableton Live), .cpr (Cubase)
Portability	Requires both .aup and _data folder to move	Single file (fully self-contained)	Mixed: some DAWs self-contained, others require asset folders
Audio Compression	Uncompressed AU format in _data folder	Compressed audio within database	Varies by DAW, typically compressed
Default Since	1999–September 2023	Audacity 3.4.0 (September 2023)	N/A—industry standard formats vary
Human-Readable	Yes (XML plain text)	No (binary SQLite database)	No (binary formats for most professional DAWs)

Why It Matters

Free Audio Editing Access: The .aup format enabled Audacity's role as one of the world's most accessible free digital audio workstations, with over 230 million total downloads as of 2023. This accessibility democratized audio editing for students, podcasters, musicians, and small content creators worldwide.
Legacy Project Management: Understanding .aup format remains essential for users with archives of older Audacity projects spanning decades. Many professionals and hobbyists maintain large libraries of .aup projects that require proper folder management and careful migration planning when upgrading to newer Audacity versions.
Format Evolution and Future Compatibility: The transition from .aup to .aup3 represents a significant architectural change in Audacity's development. Projects created in .aup format can still be imported and converted in Audacity 3.4.0 and later, but users must understand the conversion process to avoid data loss.

While .aup format is becoming legacy as Audacity shifts to .aup3, it remains crucial for understanding the software's history and managing existing projects. Users working with .aup files should maintain organized folder structures, backup both the .aup file and _data folder together, and plan migration strategies if upgrading to newer Audacity versions that default to .aup3 format.