AU to AIFF Converter

Convert AU to AIFF: What This Tutorial Covers

This walks through bringing a legacy Sun/NeXT .au (or .snd) clip into an AIFF file that Logic Pro, GarageBand, QuickTime, and Mac-side Pro Tools read natively. The result depends entirely on what's inside the AU: a linear-PCM .au re-wraps losslessly into AIFF, while an 8 kHz μ-law .au is decoded to 16-bit PCM — a much bigger file that does not, and can not, sound better than the original.

How to Convert AU to AIFF

1. Upload Your AU File: Drag and drop or click "+ Add Files" to select .au or .snd files. Sun/NeXT workstation recordings, Java 1.0/1.1 applet sound assets, Solaris/SPARCstation desktop sounds, and old academic speech corpora all work. Batch is supported — drop an entire archive folder in one pass.
2. Set Audio Sample Rate: Leave Audio Sample Rate on "Original" for a true 1:1 copy. Classic μ-law .au files are usually 8 kHz — keep that rate; resampling to 44.1/48 kHz makes the file bigger without adding any detail above the source's ~4 kHz bandwidth.
3. Set Audio Channel and Trim (Optional): Use Audio Channel to keep "Original" (most .au files are mono) or fold to mono/stereo for a target tool. Use Trim (default "Unchanged") with a start time and duration to pull a single sample out of a longer capture.
4. Convert and Download: Click "Convert" and download your AIFF. The converter writes 16-bit big-endian PCM (PCM_S16BE), the native AIFF encoding Apple's apps expect. No sign-up, no watermark.

Walk-through: PCM Re-wrap vs μ-law Decode

AU and AIFF are both legacy big-endian containers, so what happens on conversion hinges on the AU's internal encoding. There are two distinct cases:

• Linear-PCM AU → AIFF is a lossless re-wrap. If the .au already holds linear PCM (for example 16-bit at 44.1 kHz), the converter writes the same samples into an AIFF header. Output is bit-faithful at the same bit depth and rate, and the file size is essentially unchanged — only the header differs.
• μ-law AU → AIFF inflates with no fidelity regain. The most common legacy .au is 8-bit μ-law at 8 kHz mono (Sun's classic default, inherited from G.711 telephony). μ-law is companded/lossy — it already discarded dynamic range at record time. Decoding it to 16-bit linear PCM for AIFF roughly doubles bytes per sample and adds nothing back. An 8 kHz μ-law source also stays telephone-bandwidth (~4 kHz of usable audio) no matter how large the AIFF becomes.
• If you want to keep the μ-law bytes untouched, AIFF-C can carry μ-law, but for a faithful 1:1 archival copy of a telephony .au the cleaner targets are a μ-law-preserving WAV or simply keeping the original .au.

Common Errors and How to Fix Them

• "My AIFF is twice the size of the AU" — Your AU was μ-law. Decoding 8-bit μ-law to 16-bit PCM doubles the per-sample size; the extra bytes are padding, not detail. If size matters more than an uncompressed master, convert to MP3 at 64–96 kbps mono instead.
• "The audio still sounds like a phone call" — An 8 kHz μ-law source is band-limited to roughly 4 kHz (the Nyquist limit of 8 kHz). AIFF cannot restore frequencies that were never captured. This is expected, not a conversion fault.
• "The file won't open / isn't recognized" — A real AU starts with the magic bytes 2E 73 6E 64 (ASCII .snd). Some 1990s .au files were corrupted by FTP transfers in ASCII mode, or are headerless raw PCM. Inspect the first four bytes; anything else isn't a standard Sun/NeXT AU and needs format identification first.
• ".snd file behaves oddly" — .snd on Sun/NeXT is the same container as .au and converts fine. But classic Mac OS System 7 also used .snd for an unrelated pre-OS-X sound resource; those rare files need a Mac-specific extractor first.
• "Output is silent" — The most common cause is a truncated or zero-length AU from an interrupted transfer. Re-download the source and check it plays in VLC or ffplay before converting.

When This Doesn't Work

A few .au files in old archives aren't really standard Sun/NeXT audio: headerless raw PCM dumps, Mac System 7 .snd resources, or files damaged by legacy ASCII-mode FTP. XConvert reads the standard 2E 73 6E 64 magic and decodes μ-law, A-law, and 8/16/24/32-bit PCM AU variants — but it can't recover a file whose header or samples are gone. If a clip fails, identify the true format first (check the leading bytes), repair the source, then convert. For DRM-wrapped or proprietary derivatives of .au, no online converter can help; you'd need the originating application.

Frequently Asked Questions

Is converting AU to AIFF lossless?

It depends on the AU's encoding. If the AU holds linear PCM, AU → AIFF is a lossless re-wrap — the same samples land inside an AIFF header at the same bit depth and rate, so it's bit-faithful. If the AU holds 8-bit μ-law (the common legacy case), the conversion decodes companded 8-bit into 16-bit linear PCM: mathematically faithful to what μ-law stored, but it can't restore the dynamic range μ-law already discarded at recording time.

Why is my AIFF so much bigger than the AU?

Because your AU was almost certainly μ-law. μ-law packs audio at about 8 KB per second (8-bit, 8 kHz mono); decoding it to 16-bit linear PCM for AIFF roughly doubles the per-sample size. The added bytes are padding from the wider sample format, not new detail — the audio is identical telephone-quality content in a larger wrapper. For a small file, use AU to MP3 instead.

Will the AIFF sound better than the original AU?

No. Conversion never adds information that wasn't in the source. An 8 kHz μ-law .au is band-limited to about 4 kHz of usable audio (the Nyquist of an 8 kHz sample rate), so even a large 16-bit AIFF stays telephone-bandwidth. The reason to convert is compatibility with Apple/pro-audio tools, not fidelity.

What bit depth and byte order does the AIFF use?

The converter writes 16-bit big-endian PCM (PCM_S16BE) by default — the native AIFF encoding Logic Pro, GarageBand, and QuickTime expect. AIFF is big-endian because it's built on Electronic Arts' IFF 85 structure; WAV is the little-endian sibling. In our testing, an 8 kHz mono μ-law .au converts to an 8 kHz mono 16-bit AIFF — same rate and channels, just a wider, uncompressed sample format.

Does the .au annotation or any metadata survive into the AIFF?

There's almost nothing to carry. The Sun/NeXT AU header has only an optional annotation field (usually blank) — no title, artist, or album tags. So the AIFF won't inherit track metadata, because the source has none. You can add metadata to the AIFF afterward in a tag editor or in Logic/GarageBand.

Should I convert to AIFF, WAV, or MP3?

Pick AIFF for Mac-native, pro-audio workflows (Logic Pro, GarageBand, Pro Tools on Mac). Pick WAV for cross-platform editing or to preserve μ-law inside a WAV wrapper for telephony tooling. Pick MP3 for a small, universally playable listening copy. A common pattern: keep the original .au, make an AIFF or WAV master for editing, and export MP3 for sharing.

How long are my files kept on your servers?

Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically a few hours after conversion — no sign-up, no watermark, never shared or made public.