Drop any file to identify it
No upload. No signup. No sending your file halfway across the internet.
We tell you what it is, right here in your browser.
Drop it!
Let go to identify this file.
Couldn't identify this file
Need to convert it? fwip it →
AU files are a relic of the Unix workstation era. Sun Microsystems designed the format for their NeXT and SunOS systems in the late 1980s, and it became the default audio format across Unix platforms. If you've ever heard a system sound on a 1990s Unix workstation, it was probably an AU file.
The format is simple: a short header followed by raw audio data, typically in µ-law encoding (8-bit, 8 kHz) — the same encoding used in telephone systems. Higher-quality variants support linear PCM at various sample rates, but the format's association with low-quality telephone-grade audio stuck.
You'll encounter AU files in legacy Unix software, Java applications (Java's audio API historically defaulted to AU), and old web audio. VLC and most media players handle them. For any modern use, convert to WAV or FLAC — there's no advantage to keeping audio in AU format.