AU to GSM Converter
Processing entirely on your device — large files may take a moment.
Sun Microsystems Audio and GSM 06.10 Speech exist for different jobs: AU is the µ-law audio format of old Unix systems and Java applets — tiny mono files from another era. Convert GSM speech recordings to WAV or MP3.
Because the whole conversion happens on your device, it is instant, unlimited and genuinely private — no accounts, no watermarks, no files on anyone's server. Multiple files are converted in one go.
How AU compares to GSM
| AU | GSM | |
|---|---|---|
| Compatibility | Legacy Unix tools | Asterisk, SoX, ffmpeg |
| Best for | Old system sounds and recordings | Telephony recordings |
How to convert AU to GSM
- 1
Select your files
Drag & drop your AU files onto the area above, or click to browse. You can add multiple files at once for batch conversion.
- 2
Convert instantly
Click "Convert to GSM". The conversion runs entirely inside your browser using WebAssembly — no upload, no queue, no waiting.
- 3
Download results
Download each converted GSM file individually, or grab everything at once as a ZIP archive.
About the AU format
AU is Sun Microsystems' audio format from the Unix workstation age: a small header followed by µ-law (or PCM) samples. Java's applet era shipped it everywhere, and old Unix sound tooling still emits it.
Modern players increasingly skip it. Converting AU to WAV preserves the samples bit-for-bit while moving the file into universal territory — the standard rescue path for system sounds and old recordings.
+ Strengths
- ✓Simple, lossless sample storage
- ✓Native to old Unix/Java tooling
! Limitations
- −µ-law flavor sounds dated and mono
- −Dropped by modern players
About the GSM format
GSM 06.10 is the speech codec of the original GSM mobile network — 13 kbit/s RPE-LTP that made digital cellphone calls possible in 1991 and still lives inside VoIP systems, old answering machines and Asterisk PBX recordings.
It is lossy speech, not music: converting GSM to WAV or MP3 preserves intelligibility perfectly while finally letting desktop players open the file without special codecs.
+ Strengths
- ✓Tiny bitrate for speech intelligibility
- ✓Ubiquitous in telephony systems
- ✓Decodes natively via ffmpeg
! Limitations
- −Speech-only quality — music falls apart
- −13 kbit/s artifacts are audible
- −8000 Hz sample rate only
Why convert AU to GSM?
Think of it as moving your file to the container that fits the job. µ-law flavor sounds dated and mono GSM works differently: Tiny bitrate for speech intelligibility If any of that sounds like your task, run the conversion — it takes seconds and nothing leaves your device.
Frequently asked questions
Is this AU to GSM converter really free?
Yes — completely free, with no sign-up, no watermark and no daily conversion limits. The site is supported by advertising.
Are my files uploaded to a server?
No. The conversion runs entirely inside your browser using WebAssembly, so your files never leave your device — that is what makes it instant and private.
Does it work on Windows, Mac, iPhone and Android?
Yes. Anything with a modern browser works: Windows, macOS, Linux, Android and iOS. No software installation is required.
Is there a file size limit for AU to GSM?
The only limit is your device's memory, since nothing is uploaded. Files up to a few hundred megabytes work fine on a modern desktop browser; very large files simply take a little longer.
Will converting AU to GSM reduce audio quality?
If GSM is lossless, the output contains everything the AU file contains — no further loss is added. If GSM is lossy, one recompression pass is unavoidable; the quality slider controls how much. Loss that already happened in the source file can never be undone by converting.
Are tags like title and artist preserved?
Tag handling varies between target formats and this conversion focuses on the audio itself. For archival copies where tags matter, keep the original file; the converted copy is for playback and sharing.