MP3 to AU Converter
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Supports: MP3
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Need help?How to Convert MP3 to AU Online
- Upload Your MP3 Files — Drag and drop or select one or more MP3 audio files.
- Choose a Quality Preset — Select from Highest, Very High (Recommended), High, Medium, Low, Very Low, or Lowest.
- Adjust Audio Settings (Optional) — Change the Audio Channel to Original, Mono, or Stereo. Set a specific Sample Rate (Original, 8000 Hz, 12000 Hz, 16000 Hz, 24000 Hz, 44100 Hz, or 48000 Hz).
- Trim (Optional) — Set a start time and duration in seconds or HH:MM:SS.sss to extract a specific segment.
- Convert & Download — Click Convert and download your AU files.
Why Convert MP3 to AU?
AU (Audio) is a simple audio format developed by Sun Microsystems for Unix and NeXT systems. It stores audio data with a minimal header, making it easy to parse programmatically. AU files are still used in telephony systems (IVR, PBX), Java audio APIs (javax.sound), legacy Unix applications, and scientific computing environments. Converting MP3 to AU is necessary when your target system or API specifically requires the AU format.
MP3 vs AU Comparison
| Feature | MP3 | AU |
|---|---|---|
| Compression | Lossy | Typically uncompressed (PCM) |
| File size (1 min, stereo) | ~1 MB at 128 kbps | ~10 MB (PCM 16-bit, 44.1 kHz) |
| Parsing complexity | Requires decoder library | Trivial — simple binary header |
Java javax.sound support |
Requires plugin | ✅ Native |
| Unix/Solaris native | ❌ | ✅ |
| Telephony (IVR/PBX) | ❌ | ✅ (mu-law 8 kHz) |
| Web browser playback | ✅ Universal | Limited |
Use Cases
- Telephony / IVR systems — Phone systems and interactive voice response platforms often require AU files at 8000 Hz mono with mu-law encoding.
- Java audio applications — The
javax.sound.sampledAPI natively supports AU without additional libraries, making it the simplest format for Java audio playback. - Legacy Unix systems — Older Solaris, SunOS, and NeXT applications expect AU format for system sounds and audio processing.
- Scientific computing — AU's simple binary structure makes it easy to read and manipulate in MATLAB, Python, and C without external dependencies.
What is an AU file?
AU is an audio file format created by Sun Microsystems. It has a simple 24-byte header followed by raw audio data, typically PCM (uncompressed) or mu-law encoded. The format is native to Unix systems and Java's audio API.
Will the AU file be larger than the MP3?
Yes, significantly. AU typically stores uncompressed PCM audio, so a 1-minute stereo file at 44.1 kHz is about 10 MB — roughly 10× larger than a 128 kbps MP3. This is expected for an uncompressed format.
What sample rate should I use for telephony?
8000 Hz mono is the standard for telephone-quality audio and IVR systems. Set the Sample Rate to 8000 Hz and Audio Channel to Mono for telephony use.
Can I batch convert multiple MP3 files?
Yes. Upload multiple MP3 files and convert them all to AU at once with the same Quality Preset and audio settings.
Is AU the same as SND?
AU files are sometimes called SND (Sound) files. The formats are essentially identical — both use the same header structure and audio encoding. Some systems use the .snd extension instead of .au.