FormatDrop
Audio Format

AU

Sun Audio File

AU (Sun Audio) is the audio format developed by Sun Microsystems for early Unix workstations and Java applets. From the late 1980s through the early 2000s, AU was the standard sound format on Solaris, NeXTSTEP, and Java-based applications. Today it's almost entirely legacy — mostly encountered when accessing archived academic, scientific, or Java applet audio.

What is AU?

An AU file consists of a 24-byte header (containing magic number '.snd', sample rate, channels, encoding type) followed by raw audio samples. Common encodings include 8-bit μ-law (telephone quality), 16-bit linear PCM (CD quality), and 32-bit floating point (high-precision recording). The format is uncompressed except for μ-law and A-law variants which provide modest compression for voice.

AU pros and cons

Advantages

  • Simple, well-documented format
  • Uncompressed PCM mode is lossless
  • Native Java audio support (legacy)
  • Big-endian byte order (matches network order)
  • Self-describing header includes all needed parameters

Limitations

  • Effectively legacy — almost no modern use
  • μ-law encoding sounds poor compared to even MP3
  • No metadata support (no artist, title, album)
  • Sun Microsystems no longer exists (acquired by Oracle 2010)
  • Less efficient than FLAC or modern codecs

When should you convert AU files?

Convert AU to WAV for use in modern audio editors — both are uncompressed PCM, so the conversion is lossless: `ffmpeg -i input.au output.wav`. Convert to MP3 or AAC for portable playback. If your AU file is μ-law encoded (telephone quality), expect lower fidelity in any output format.

Convert AU files

AUDIO-CONVERTER→

All FormatDrop conversions run entirely in your browser — no file upload, no server processing. Your files stay on your device.

AU FAQ

What's the difference between AU and WAV?
Both contain uncompressed PCM audio. AU uses big-endian byte order (samples stored most significant byte first); WAV uses little-endian. AU has a simpler header (24 bytes); WAV uses RIFF chunks. AU supports μ-law and A-law compression; WAV mostly uses PCM. The conversion between them is a lossless byte-order swap.
How do I play an AU file?
VLC plays AU files on every platform. Audacity opens them for editing. On Linux: `play input.au` (sox). On macOS: `afplay input.au`. Quicktime supports AU on macOS. Windows Media Player does NOT support AU natively.
Where do I find AU files in 2026?
Sound effect libraries from the 1990s, archived Java applets, academic recordings from Unix-era research labs, telephone system test files (μ-law AU is common in PBX testing), and old Sun/SGI software bundles. Almost no modern software produces AU.

More formats

HEICWebPAVIFEPUBWebMOpusMP3WAVM4AFLACAACMP4AVIMKVMOVJPGPNGGIFSVGTIFFICOBMPEPSARWOGGWMVPPTXPagesPDFDOCXRAWHEVCH.264AIFFM4VWMA3GPDNGRTFPSDOGVTSFLVAIXLSXCSVZIPAPNGMIDIJPEG XLMPG/MPEGVOBM2TSAC3ALACDTSJP2HEIFAPECBZ3G2SRTDOCPPTXLSODTODSM3URAR7ZM4BAMRTXTMOBITARGZJSONXMLYAMLKEYMTSCR2NEFMXFTGACAFASSVTTDSFRMF4VWVASFRMVBORFRW2EAC-3TTAISODMGXZDjVuFB2M4RAZW3MKAEXRVCFICSAAXPRCMP2SPXXSPFM3U8