M4A to AU Converter
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Supports: M4A
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Need help?How to Convert M4A to AU
- Upload Your M4A File — Click "Choose Files" or drag and drop your M4A (MPEG-4 Audio) file. Only .m4a files are accepted.
- Set Audio Channel — Under Audio Channel, choose Original, Mono, or Stereo. AU files are commonly mono for system sounds.
- Set Sample Rate — Under Audio Sample Rate, choose from 8000 Hz through 48000 Hz. Common AU sample rates are 8000 Hz (telephony) and 44100 Hz (CD quality).
- Trim (Optional) — Under Trim, set a Start Time and Duration in seconds or HH:MM:SS.sss format.
- Convert & Download — Click "Convert" and download your AU file.
Why Convert M4A to AU?
M4A is Apple's audio format using AAC compression. AU (Audio file format) was developed by Sun Microsystems for Unix systems. It stores uncompressed PCM audio data. Converting M4A to AU is useful for Unix/Linux system sounds and audio applications, Java audio APIs (javax.sound.sampled) that prefer AU input, scientific and research applications requiring raw PCM data, and legacy Solaris and NeXTSTEP audio workflows.
M4A vs AU Comparison
| Feature | M4A (AAC) | AU (Sun Audio) |
|---|---|---|
| Developer | Apple | Sun Microsystems |
| Compression | Lossy (AAC) | Uncompressed (PCM) |
| File size (1 min, stereo) | ~1 MB at 128 kbps | ~10 MB at 44100 Hz |
| Audio quality | Good (lossy) | Perfect (lossless PCM) |
| Platform | Apple ecosystem | Unix/Linux, Java |
| Best for | Music, podcasts | System sounds, scientific |
Common AU Sample Rates
| Sample Rate | Quality | Use Case |
|---|---|---|
| 8000 Hz | Telephone | VoIP, system alerts |
| 22050 Hz | AM radio | Simple sound effects |
| 44100 Hz | CD quality | Music, high-quality audio |
| 48000 Hz | Broadcast | Professional audio |
Why is the File Compression section not available?
AU is an uncompressed PCM format — there are no compression options because the audio data is stored raw. The output file will be significantly larger than the M4A source. Use Mono channel and a lower sample rate to reduce file size.
Will the AU file be much larger than the M4A?
Yes. AU stores uncompressed PCM data, so a 1 MB M4A file at 128 kbps becomes roughly 10 MB as AU at 44100 Hz stereo. To minimize size, convert to Mono and use 8000 Hz sample rate for voice content.
What applications use AU files?
Java audio APIs (javax.sound.sampled), Unix/Linux system sounds, Audacity, MATLAB, and legacy Sun Solaris applications. AU is also used in scientific computing for raw audio data processing.
Can I trim the audio during conversion?
Yes. Under Trim, switch to "Trim" and enter a Start Time and Duration. This extracts a specific segment, which also reduces the output file size.
Does AU support stereo audio?
Yes. AU supports both mono and stereo. Under Audio Channel, choose Stereo to preserve both channels or Mono to halve the file size.