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Need help?How to Convert M4R to AU
- Upload Your M4R File: Drag the
.m4rringtone onto the page or click "+ Add Files". You can queue several files and convert them with the same settings. - Set Audio Channel: "ORIGINAL" keeps the tone's layout. "MONO" halves the size and is usually right for alert and notification sounds; "STEREO" keeps both channels for music.
- Choose a Sample Rate and Trim (Optional): Keep Audio Sample Rate on "ORIGINAL", or pick 8000 Hz for a telephone-style clip, 16000 Hz for compact voice, or 44100 / 48000 Hz for music. Trim cuts the tone down to the part you need.
- Convert and Download: Click Convert and save the
.au. Files are uploaded over TLS, processed on our servers, and deleted automatically after a few hours. Free, with no sign-up and no watermark.
A Ringtone as a Unix or Java Sound
An M4R is the file an iPhone uses for custom ringtones: AAC-LC audio in an MPEG-4 container, the same structure as an M4A, with an extension that marks it as a tone. Apple says ringtones can be up to 30 seconds long, which makes M4R files natural candidates for alerts, chimes and notification sounds — the very job AU files have done on Unix systems for decades.
AU is Sun Microsystems' audio format, also seen with the .snd extension on NeXT machines. It could hardly be simpler: a big-endian header that starts with the magic bytes .snd, gives the data offset, size, encoding, sample rate and channel count, followed by the raw samples. That simplicity is why it is still useful:
- Java. The Java Sound API (
javax.sound.sampled) reads AU, AIFF and WAV without extra libraries, while AAC needs a third-party decoder. A ringtone saved as AU drops straight into a Java desktop app or tool as an alert sound. - Unix tools. SoX, FFmpeg, Audacity and many command-line utilities read AU natively, and some older Unix workstations and scripts expect it.
- Telephony. 8 kHz mu-law is the G.711 encoding used on telephone networks, so an 8 kHz mono AU from this page is a natural fit for systems that speak G.711.
What This Page Writes
The AU files written here use 8-bit mu-law encoding. There is no codec selector and no File Compression section on this page; the settings that shape the output are Audio Channel, Audio Sample Rate and Trim. Mu-law stores each sample in 8 bits on a logarithmic scale, which keeps far more dynamic range than plain 8-bit audio — it is the encoding classic AU files were known for.
Be clear about quality: the AAC in your ringtone is already lossy, and mu-law adds a small amount of quantisation noise on top, most noticeable in quiet passages. Ringtones are usually loud and short, so this rarely matters. If you need 16-bit linear PCM instead, M4R to WAV or M4R to AIFF are the better targets.
M4R vs AU
| Property | M4R (input) | AU (output) |
|---|---|---|
| Origin | Apple's ringtone extension for MPEG-4 audio | Sun Microsystems; .snd on NeXT |
| Header | MPEG-4 boxes | Simple big-endian header starting with .snd |
| Audio on this page | AAC-LC, lossy | 8-bit mu-law |
| Bytes per sample | Not applicable (compressed) | 1 per channel |
| Metadata | MPEG-4 tags | Optional free-text annotation only |
| 30 s, mono, 8 kHz | not typical for AAC | about 240 KB |
| Readers | iPhone, Mac, iTunes, most players | Java Sound, SoX, FFmpeg, Audacity, Unix tools |
| Best for | Ringing an iPhone | Alerts in Java and Unix software, G.711 telephony |
AU Size by Sample Rate and Channels
With mu-law, every sample is one byte, so size is sample rate × channels × seconds.
| Sample rate and channels | 3-second alert | 30-second tone | Suits |
|---|---|---|---|
| 8000 Hz, mono | about 24 KB | about 240 KB | Telephony, terminal-style beeps |
| 16000 Hz, mono | about 48 KB | about 480 KB | Clear speech prompts |
| 44100 Hz, mono | about 132 KB | about 1.3 MB | Music alerts in mono |
| 44100 Hz, stereo | about 265 KB | about 2.6 MB | Music with stereo width |
| 48000 Hz, stereo | about 288 KB | about 2.9 MB | Matching 48 kHz video or app audio |
For an alert sound, 16000 or 44100 Hz mono and a trimmed 2–5 second clip usually give the best balance of clarity and size.
Frequently Asked Questions
What encoding does the AU file use?
8-bit mu-law, the classic AU encoding. This page has no codec selector, so every AU it writes uses mu-law. If a tool needs 16-bit linear PCM, convert to WAV or AIFF instead.
Will Java play the AU file?
Yes, the Java Sound API reads AU files directly through AudioSystem.getAudioInputStream. If a particular Clip or line on your JVM will not accept mu-law, convert the stream with AudioSystem.getAudioInputStream(AudioFormat.Encoding.PCM_SIGNED, stream) and play the result.
Why is the AU larger than the M4R?
AAC is a perceptual codec that compresses heavily; mu-law simply stores one byte per sample. At 44.1 kHz stereo that is about 88 KB per second, compared with about 16 KB per second for a 128 kbps ringtone. Choosing mono and a lower sample rate brings the AU much closer to the M4R's size.
Does converting to AU improve the sound?
No. The AAC encode already removed some detail, and mu-law's 8-bit companding adds a little noise of its own. The AU is about compatibility with Java, Unix and telephony tools, not fidelity.
Which sample rate should I pick?
8000 Hz for anything headed to a telephone system, 16000 Hz for a clear voice prompt, and 44100 or 48000 Hz to keep a musical tone sounding like the original. "ORIGINAL" keeps whatever rate the ringtone already has.
Will the tone's name and tags carry over?
No. AU has only an optional free-text annotation field and no standard tags or artwork. Give the file a descriptive name, and keep the original .m4r if the metadata matters.
Can I turn an AU file into an iPhone ringtone?
Yes, AU to M4R goes the other way. Keep the result to 30 seconds or less, the ringtone length Apple documents.
How are my files handled?
Files are uploaded over an encrypted (TLS) connection, processed on our servers, and deleted automatically a few hours after processing. No account is needed and nothing is watermarked. Other formats for the same ringtone are listed on the M4R Converter.