AIFF to AU Converter

AIFF to AU Converter

AU — the Sun/NeXT audio format, also seen with the .snd extension — is one of the oldest audio containers still in circulation: a short big-endian header followed by raw sample data. It survives because Unix toolchains, Java Sound and a lot of telephony and speech-research software read it without any extra library. This converter takes Apple's AIFF (uncompressed linear PCM) and writes a .au file encoded as 8-bit G.711 mu-law, the format's classic payload and the one legacy tools are most likely to expect.

AIFF Format at a Glance

AU (Sun/NeXT) Format at a Glance

How to Convert AIFF to AU

1. Upload Your AIFF File: Drag .aif or .aiff files onto the page or click "+ Add Files". Multiple files can be queued and share the same settings.
2. Set the Audio Sample Rate: Leave Audio Sample Rate on ORIGINAL to keep the source rate, or pick 8000 HZ for classic telephony-style AU, 16000 HZ for speech-recognition input, or 44100/48000 HZ to stay at production rate.
3. Set Audio Channel and Trim: Audio Channel takes ORIGINAL, MONO or STEREO — fold to MONO for voice work, which also halves the file. Trim exports just a start time and duration when you only need a section.
4. Convert and Download: Click Convert and save the .au. No sign-up, no watermark.

What the mu-law Encoding Does to Your Audio

G.711 mu-law is companding, not a modern codec: it squeezes each linear sample onto a logarithmic scale so that quiet passages keep their resolution while loud ones lose it. Each 14-bit linear input sample comes out as one byte, which is why the arithmetic is so simple — one byte per sample per channel, no frames, no bitrate negotiation, no variable-rate anything.

The trade is bandwidth and dynamic range. Speech at 8 kHz mono sounds like a telephone call because that is literally the encoding telephone networks standardised on; music at 44.1 kHz keeps its full frequency range but picks up the quantisation noise floor of an 8-bit companded scale. If neither is acceptable, AU is the wrong container for the job.

Frequently Asked Questions

Is converting AIFF to AU lossless?

No. AIFF holds linear PCM, and the AU files produced here are 8-bit G.711 mu-law, which is a lossy companding scheme — the mapping from 14-bit linear to 8 bits cannot be undone. Keep the AIFF as your master. If you need a container swap that preserves linear PCM, AIFF to WAV is the conversion you actually want.

Why is my AU file exactly half the size of the AIFF?

Because mu-law writes one byte where 16-bit PCM writes two, and neither format has any framing overhead worth counting. Our encoder keeps the source sample rate and channel count unless you change them, so a 3-minute 44.1 kHz stereo AIFF of about 31.8 MB becomes 44,100 × 2 channels × 1 byte × 180 s ≈ 15.9 MB as mu-law AU. Drop to 8 kHz mono and the same three minutes is about 1.4 MB.

What software still opens .au files?

VLC, Audacity, SoX, ffmpeg and mpv all read AU directly, and Java's javax.sound.sampled treats it as a first-class file type alongside AIFF and WAVE. What will not open it: phones, web pages, and most consumer media libraries — no mainstream mobile OS or browser ships an AU handler. That is exactly why AU is a delivery format for specific toolchains rather than a general-purpose one.

Is .au the same thing as .snd?

Yes. Sun used .au, NeXT used .snd, and both write the same header — the file even begins with the ASCII bytes .snd regardless of which extension it carries. Renaming between the two extensions does not change the contents, though a given program may only recognise one of them.

Should I resample to 8 kHz?

Only if the receiving system expects telephony audio. 8 kHz mono mu-law is the classic AU profile — it is what Sun's /dev/audio produced, what old Java applet sound assumed, and what IVR and voicemail systems use at 64 kbps per channel. For speech-recognition corpora, 16 kHz mono is the more common requirement. For anything musical, leave Audio Sample Rate on ORIGINAL.

Can an AU file be stereo and 44.1 kHz, or is it always telephone audio?

The header has explicit sample-rate and channel-count fields, so stereo at 44.1 or 48 kHz is perfectly legal AU and this converter will write it. The 8 kHz mono convention comes from telephony practice, not from any limit in the format. Note that not every legacy reader honours the header — a few very old tools assume the classic profile and will misplay anything else.

Do the AIFF's title, markers and loop points survive?

No. AU has a single free-text annotation field and nothing else, so AIFF's NAME, AUTH and ANNO text has at best one place to land, and structured data — MARK markers, INST loop points and key ranges — has none. Keep the AIFF if that information matters.

Why does my AU sound like a telephone call?

That is mu-law working as designed. G.711 was built to carry intelligible speech in 64 kbps per channel, and its noise floor is audible on music and on quiet detailed material. If the result needs to sound like the source, convert to FLAC for a lossless copy or MP3 for a small lossy one, and use AU only where the .au container itself is the requirement.

Are my files private when I convert them here?

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

For the reverse direction, see AU to AIFF.