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, and the default AU output here is 8-bit µ-law — a lossy, telephone-grade companding — so converting reduces quality rather than gaining any; for a full-fidelity copy, select 16-bit PCM (PCM_S16BE) in the advanced options, at the cost of a larger file. 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 — a lossy, telephone-grade companding scheme — and that is exactly this converter's default output (at whatever sample rate you choose). Each sample is companded into 8 bits, so the audio inside your .au is not bit-identical to the FLAC: dynamic-range detail is lost. If you need a lossless copy, select 16-bit big-endian linear PCM (PCM_S16BE) in the advanced options; that undoes FLAC's compression, so the file commonly grows to roughly 1.5x–2x the original FLAC. With the µ-law default the size stays broadly comparable to a CD-quality FLAC — one byte per sample per channel — but you are paying fidelity, not bytes.

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 — by default it slightly reduces it. FLAC is already lossless and holds the exact original samples, but the converter's default AU encoding is 8-bit µ-law, which packs each sample into 8 bits with a telephone-grade logarithmic curve. For a bit-identical copy of a 16-bit FLAC, select 16-bit linear PCM (PCM_S16BE) in the advanced options. Either way the converter does not upsample — a 44.1 kHz FLAC produces a 44.1 kHz AU, not a higher-resolution one.

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

Yes, by default. The historic .au from old Unix workstations was 8-bit µ-law, and that is what this converter writes unless you choose otherwise — so the output matches legacy tools that expect µ-law (at the sample rate you select; pick 8000 Hz mono for the classic profile). If you instead want full-fidelity linear PCM in the AU container, select 16-bit big-endian PCM (PCM_S16BE) in the advanced options; A-law (PCM_ALAW) is also available for European telephony pipelines.

How big will the AU file be compared to the FLAC?

With the default 8-bit µ-law encoding the AU stores one byte per sample per channel — about 5.3 MB per minute at 44.1 kHz stereo — which lands broadly in the same range as a typical CD-quality FLAC. If you select 16-bit PCM (PCM_S16BE), the payload is uncompressed at roughly 10 MB per minute for 16-bit/44.1 kHz stereo, so the file commonly expands to 1.5x–2x the FLAC. Either way the bytes buy you the container, 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; if you select 16-bit PCM the sample words are big-endian too, while the default 8-bit µ-law samples are single bytes, so byte order affects only the header. 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?

Only if you selected 16-bit PCM (PCM_S16BE) for the AU — a PCM AU holds the exact samples, so re-encoding to FLAC recovers them bit-for-bit. With the default 8-bit µ-law output, the companding has already discarded dynamic-range detail; converting back to FLAC is lossless from that point on, but the audio will not be identical to the original FLAC. Our AU to FLAC tool does the reverse conversion.

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. A 16-bit/44.1 kHz stereo FLAC converts to a same-rate µ-law AU of broadly similar size; selecting 16-bit PCM instead roughly doubles the payload and keeps the samples bit-identical.

Will my FLAC tags and cover art carry over to the AU file?

No. FLAC stores rich metadata — Vorbis comment tags, embedded cover art, and cue sheets — but the AU format has only a minimal header with a single free-text annotation field and no standard tag structure. So artist, album, and artwork are dropped in the conversion; the .au keeps the audio samples but not the tagging. If preserving metadata matters, keep the FLAC or choose a format that supports tags.