FLAC to AU Converter

FLAC to AU Converter

AU (also seen as .snd) is the Sun Microsystems audio format from the late-1980s Unix workstation era, later carried over to NeXT systems and used widely as the native /dev/audio sound format on early Unix. This converter turns a FLAC file into an .au file for the narrow cases where a legacy Unix tool, an old Java program, or a retro-computing pipeline specifically expects that container. Be clear on what it does for fidelity: FLAC already holds the exact, bit-perfect samples losslessly, so wrapping them in AU gains a container format, not quality — and because the AU output here is uncompressed PCM, the file gets larger. Most people are better off keeping the FLAC, or using FLAC to WAV for a plain editor-friendly master.

FLAC Format at a Glance

AU Format at a Glance

What This Converter Actually Writes Into the AU

The classic .au most people associate with old Unix systems is 8-bit µ-law at 8 kHz — a lossy, telephone-grade companding scheme. This converter does not produce that. It writes 16-bit big-endian linear PCM inside the AU container, which is the AU muxer's default and a lossless encoding. So the audio inside your .au is bit-identical to the FLAC, just stored uncompressed and in big-endian byte order. The trade-off is size: FLAC's lossless compression is undone, so a converted file commonly grows to roughly 1.5x–2x the original FLAC. You are paying bytes to gain the container, not losing audio.

How to Convert FLAC to AU

1. Upload Your FLAC File: Drag and drop your .flac files onto the page or click "+ Add Files". You can queue several and convert them with the same settings.
2. Set Audio Channel and Audio Sample Rate: Leave Audio Channel and Audio Sample Rate on "Original" for a true 1:1 copy of the source audio; change them only if a target device needs mono or a specific sample rate.
3. Trim (Optional): Use the Trim control to export just a section of the track, or leave it "Unchanged" to convert the whole file.
4. Convert and Download: Click "Convert" and download your AU file. No sign-up, no watermark.

Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion — never shared or made public.

Frequently Asked Questions

Will converting FLAC to AU improve the audio quality?

No. FLAC is already lossless and holds the exact original samples, and this converter writes those same samples into the AU as 16-bit linear PCM. The output is bit-identical to the source — you gain the .au container, not fidelity. The converter does not upsample, so a 16-bit/44.1 kHz FLAC produces a 16-bit/44.1 kHz AU, not a higher-resolution one.

Does the AU output use 8-bit µ-law like classic Unix .au files?

No. The historic .au format people remember from old Unix workstations was 8-bit µ-law at 8000 Hz, which is lossy and telephone-grade. This converter instead writes 16-bit big-endian linear PCM — the AU container's lossless default — so it keeps full CD-or-better quality rather than down-converting to µ-law. If a legacy tool specifically requires 8-bit µ-law, this output will not match that exact encoding.

Why is my AU file so much larger than the FLAC?

Because the AU payload here is uncompressed. FLAC shrinks audio losslessly, typically to about half its uncompressed size, while the linear PCM inside the AU writes every sample out in full. CD-quality stereo runs around 10 MB per minute at 16-bit/44.1 kHz, so a FLAC commonly expands to roughly 1.5x–2x its original size as AU. The extra bytes are uncompressed data, not added detail.

Why would I convert to AU at all instead of keeping FLAC?

Only for compatibility with something that specifically expects .au. Realistic cases: a legacy Unix or NeXT-lineage program that reads the Sun audio format natively, older Java code that loads .au via the classic sound APIs, or an academic/retro-computing pipeline that documents .au as its interchange format. For listening, storage, or editing, FLAC or FLAC to WAV is the better choice — AU offers no advantage there.

Is the AU output big-endian, and does that matter?

Yes. The AU format stores its header and sample data in big-endian byte order, and the 16-bit PCM this converter writes follows that. It matters only if a downstream tool reads the raw bytes assuming little-endian — well-behaved players honor the header and handle it correctly. WAV, by contrast, is little-endian, which is one of the technical differences between the two containers even though both can carry the same PCM samples.

Can I convert the AU back to FLAC later without losing anything?

Yes. Because the AU here holds uncompressed lossless PCM, re-encoding it to FLAC recovers the exact same samples and re-applies lossless compression — no quality loss, just a smaller file again. Our AU to FLAC tool does the reverse conversion. (This round-trip is lossless only because the output is PCM; it would not be if the AU were 8-bit µ-law.)

How long do my uploaded files stay on your servers?

Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion. They are never shared or made public, there is no watermark, and no sign-up is required. In our testing, a 16-bit/44.1 kHz stereo FLAC produced a same-rate 16-bit AU with identical audio and a noticeably larger file size, as expected from dropping FLAC's compression.