AU to FLAC Converter

Convert AU to FLAC Online

Move legacy AU audio — the Sun/NeXT workstation format (extension .au or .snd) once used for Unix system sounds and early Java applets — into FLAC, the modern free lossless codec. The conversion is lossless: every sample in the source is preserved exactly, and FLAC's compression usually shrinks linear-PCM AU files by roughly 30–60% while keeping full fidelity and adding proper metadata tags the AU container never supported.

How to Convert AU to FLAC

1. Upload Your AU File: Drag and drop or click "+ Add Files" to select .au or .snd recordings. Sun/SPARCstation desktop sounds, Java 1.0/1.1 applet audio, and old Unix speech archives all work. Batch upload is supported for migrating a whole folder at once.
2. Set the Compression Level: Use the Compression level slider (1–12). Higher values squeeze the file smaller and take a little longer to encode; the audio is bit-for-bit identical at every level because FLAC is lossless — the slider only trades encode time for file size, never quality.
3. Adjust Sample Rate, Channels, or Trim (Optional): Leave Audio Sample Rate and Audio Channel on "Original" to copy the AU's native rate and layout untouched (the lossless path), or change them to resample/remix. Use Trim to keep only a section of a longer capture.
4. Convert and Download: Click Convert. Files are processed on our servers and download individually or as a ZIP — no sign-up, no watermark.

AU vs FLAC — Format Comparison

Frequently Asked Questions

Will converting my AU file to FLAC improve the sound quality?

No — and the reason depends on what's inside the AU. FLAC is lossless, so it preserves exactly what the source contains but cannot add detail that was never recorded. If your AU holds 8-bit µ-law or A-law audio (the classic Sun telephone-companded default), the FLAC will sound identical to the AU — same limited 8 kHz, ~4 kHz-bandwidth fidelity — just in a modern, tagged container. If your AU holds linear PCM (16/24/32-bit), the FLAC is a genuine lossless copy of that full-quality audio at a smaller size. Either way you keep what you had; you do not regain quality that the original capture never had.

How can I tell whether my AU is µ-law or linear PCM before converting?

Open the file in a tool that reports the codec — VLC's Tools → Codec Information, the free MediaInfo app, or ffprobe file.au. Look at the codec line: "pcm_mulaw" or "pcm_alaw" means it is 8-bit companded (FLAC will preserve it but the file may not shrink much, since companded data is already compact), while "pcm_s16be" or higher means linear PCM, where FLAC gives you a real lossless size win. A sample rate of 8000 Hz with one channel is the tell-tale signature of a classic Sun µ-law recording.

What FLAC compression level should I choose?

For archival, the highest level is a reasonable default — the audio is identical at every setting, so you are only deciding how hard the encoder works to shrink the file. Higher levels produce a slightly smaller file at the cost of a little more encode time; lower levels encode faster but save less space. Decode speed and playback compatibility are the same regardless of the level you pick, so there is no downside to favoring smaller files.

Does FLAC keep more metadata than the AU file had?

Yes — and there is essentially none to lose. The AU container has no real tagging system; its header carries only an optional NULL-terminated annotation string that most files leave blank and most players ignore. FLAC supports Vorbis comments, so after converting you can add title, artist, album, date, and even embedded cover art in any tag editor (Mp3tag, Kid3, MusicBrainz Picard) — giving these legacy recordings proper, searchable metadata for the first time.

How are my files handled, and how long do you keep them?

Files are uploaded over an encrypted connection, converted on our servers, and deleted automatically a few hours after conversion — never shared, never made public, with no sign-up and no watermark. In our testing, a 60-second 16-bit/44.1 kHz stereo PCM AU (about 10 MB) converted to a FLAC of roughly 6 MB with bit-identical audio, while an 8 kHz µ-law AU stayed close to its original size because companded data leaves little for lossless compression to remove. Need a smaller, shareable copy instead of a lossless one? Convert to MP3, or reverse the process anytime with FLAC to AU.