aum

.aumAU file format (Audio)

Sun Microsystems · 1987

Developer
Sun Microsystems
Category
Audio
MIME Type
audio/x-au
First Released
1987
Open Format
Yes
File Signature
0x2E 0x72 0x61 0x77 (' .raw') or 0x44 0x45 0x46 0x49 ('DEFI') for some variants
At a Glance
.aum
AU file format (Audio)

The .aum format is a basic, uncompressed audio file format primarily used for simple sound playback, especially in older Unix environments.

Reviewed on July 14, 2026
Compression
Uncompressed (PCM) or µ-law/A-law compressed
Transparency
No
Editability
Medium
Best for
Basic sound playback

Key Features

  • Uncompressed or simple compressed audio data.
  • Includes a header for metadata.
  • Widely supported in Unix-like environments.
  • Simple and easy to parse.

Best For

  • Applications requiring simple, uncompressed audio.
  • Situations needing compatibility with older Unix systems.
  • When raw audio data manipulation is primary.
  • Low-resource environments that don't need complex audio features.

Less Ideal For

  • High-fidelity music distribution.
  • Reducing file sizes for web streaming.
  • Complex audio editing with multiple tracks.
  • Archiving large sound libraries where space is a concern.

Common Use Cases

  • Storing basic sound effects in older operating systems.
  • Simple voice recordings for system alerts.
  • Archiving raw audio data for specific scientific or technical applications.
  • Interoperability with legacy audio tools.

How to Open It

  1. Use a versatile audio player like VLC Media Player on any operating system.
  2. Open with professional audio editing software like Audacity.
  3. Attempt playback directly in some web browsers or older operating systems.
  4. Use command-line tools like `sox` on Linux/macOS for conversion or playback.

What is a .aum file?

The .aum file extension is associated with the AU (Audio) file format, which was originally developed by Sun Microsystems. It's a simple, uncompressed audio format often used in early Unix systems and for basic sound playback. While not as widespread as formats like WAV or MP3 today, AU files are recognized for their straightforward structure and broad compatibility across various audio software. They typically store raw audio data, making them efficient for certain specialized applications where fidelity and minimal processing are key.

Programs That Open .aum Files

PlatformProgram
WindowsVLC Media PlayerFree
AudacityFree
macOSVLC Media PlayerFree
AudacityFree
QuickTime PlayerFreeOfficial
LinuxVLC Media PlayerFree
AudacityFree
SoX (Sound eXchange)Free
AndroidVLC for AndroidFree
iOSVLC for MobileFree
Web BrowserOnline Audio ConvertersFree

How to Convert .aum Files

FormatMethod
.WAVAudacity, VLC Media Player, SoX
.MP3Audacity, VLC Media Player, Online Converters

Common Problems with .aum Files

⚠️ Cannot play .aum files directly on modern devices.
Use a compatible media player like VLC or convert the file to a more common format like WAV or MP3.
⚠️ Poor audio quality if originally encoded with µ-law or A-law.
Convert to an uncompressed format like PCM WAV for better fidelity, if the original quality is acceptable.

Frequently Asked Questions

Is .aum a lossless audio format?

It can be, if it stores uncompressed PCM audio. However, it often uses µ-law or A-law compression, which is a form of lossy compression, though typically applied for voice rather than music.

Why is AU format still relevant?

Its relevance lies in legacy systems, simple sound implementation in older software, and as a basic format for raw audio data, especially in Unix-like environments.

What is the difference between .au and .aum?

Typically, '.au' is the primary extension for the AU Audio format. '.aum' may sometimes be used, but often refers to the same underlying format or a variant with a similar header structure.

Technical Details

AU files are typically headered raw audio files. The header contains information about the encoding, sample rate, and number of channels. The rest of the file is raw audio data, often encoded using µ-law or A-law compression, though uncompressed PCM is also common. Its structure makes it straightforward to parse and process.

Did You Know?

The AU file format was one of the first standardized audio formats on the internet.
It's often associated with the iconic "Bonk" sound from the Solaris operating system.

Security Information

AU files themselves are generally safe, containing only audio data. However, as with any file, exercise caution when downloading from untrusted sources, as malicious actors could potentially embed harmful code in companion files or exploit vulnerabilities in the player software.

Related Extensions