AU to AMR Converter
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Supports: AU
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Need help?AU to AMR Converter
AU is the Sun Microsystems audio format from the Unix and NeXT era; AMR is the Adaptive Multi-Rate speech codec built for mobile phone calls and voice memos. This conversion makes sense when your .au file holds speech — a voice recording or telephone-grade clip you want to shrink for an MMS, a 3GP container, or an old handset. AMR-NB is a narrowband mono speech codec, so it is the right target only for voice. If the AU carries music or general audio, AMR will sound muffled and telephone-quality; convert to MP3 or WAV instead.
AU Format at a Glance
| Property | Value |
|---|---|
| Full name | Sun/NeXT audio (.au, .snd) |
| Origin | Sun Microsystems, introduced 1992 |
| Header | 24-byte header (data offset, encoding, sample rate, channels) |
| Typical payload | 8-bit μ-law (G.711) or A-law; also linear PCM and ADPCM |
| Classic use | 8 kHz telephone-grade voice on Unix systems; Java sound |
| Channels | Mono or stereo, depending on the source |
| Best for | Legacy Unix/Java audio; short voice clips |
AMR Format at a Glance
| Property | Value |
|---|---|
| Full name | Adaptive Multi-Rate Narrowband (AMR-NB) |
| Standardized by | 3GPP, adopted in the late 1990s |
| File signature | #!AMR\n magic bytes at the start of the file |
| Sample rate | 8 kHz, mono only |
| Audio bandwidth | 200–3400 Hz (narrowband, voice-only) |
| Bit-rate modes | 4.75, 5.15, 5.90, 6.70, 7.40, 7.95, 10.2, 12.2 kbit/s |
| Built for | GSM/UMTS voice calls, MMS, voice memos, .3gp |
How to Convert AU to AMR
- Upload Your AU File: Drag and drop your
.auor.sndfile, or click "+ Add Files" to pick it from your computer. You can queue several files and apply the same settings to all of them. - Set the Audio Channel and Sample Rate: AMR-NB is mono at 8 kHz, so leave Audio Channel on "Mono" and Audio Sample Rate on "8000 HZ"; the encoder downmixes and resamples to match.
- Pick the Constant Bitrate: Choose an AMR-NB mode under Constant Bitrate — 12.2 kbit/s for the best clarity, or as low as 4.75 kbit/s for the smallest file. Toll-quality speech starts around 7.4 kbit/s.
- Convert and Download: Click "Convert" and download your
.amrfile. No sign-up, no watermark.
Frequently Asked Questions
Will my AU music sound bad after converting to AMR?
Yes, if the AU holds music or general audio. AMR-NB is a narrowband speech codec: it downsamples to 8 kHz mono and keeps only the 200–3400 Hz voice band, so cymbals, bass, and stereo imaging are lost and the result sounds like a phone call. AMR is the right target only for speech. For music, convert your AU to MP3 or WAV instead.
Is converting AU to AMR lossy?
Yes, and it cannot be undone. AMR-NB is a lossy speech codec, and even if your source AU is already 8-bit μ-law (telephone-grade), re-encoding throws away detail. Converting back to a high-fidelity format later will not restore the original quality — the discarded frequencies are gone for good.
What is the difference between AMR-NB and AMR-WB?
AMR-NB (narrowband) samples at 8 kHz and covers 200–3400 Hz — standard phone-call quality. AMR-WB (wideband) samples at 16 kHz and covers roughly 50–7000 Hz, so voices sound noticeably fuller. This page produces AMR-NB, the variant most phones and MMS gateways expect; pick it if you need broad device compatibility.
Which bitrate should I choose for an AU voice recording?
For a clean voice memo, 12.2 kbit/s gives the best AMR-NB clarity. Drop to 7.40 kbit/s for a good size-versus-quality balance (this is roughly where toll-quality speech begins), or 4.75 kbit/s when file size matters more than fidelity. In our testing, a one-minute mono voice clip at 7.40 kbit/s lands near 55 KB.
What plays an AMR file once it is converted?
AMR is supported natively by most Android phones, many feature phones, and players like VLC and QuickTime (with the right components). It is the format MMS messages and .3gp recordings use. On desktop, if an .amr file will not open, VLC is the most reliable player; otherwise convert it to MP3 for universal playback.
Is my file kept private during conversion?
Your AU file is uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours. There is no sign-up, no watermark, and your files are never shared or made public.
Why is my AMR file so much smaller than the source AU?
AMR-NB is built for tight mobile bandwidth: it encodes speech at 4.75 to 12.2 kbit/s, far below the bitrate of an uncompressed or μ-law AU. A minute of PCM AU can be several megabytes, while the same minute as AMR-NB is measured in tens of kilobytes. The shrinkage comes from discarding everything outside the 200–3400 Hz voice band, so it is expected — not a sign the file is broken.
Will AMR keep the stereo channels from my AU file?
No. AMR-NB is mono only, so a stereo AU is downmixed to a single channel during conversion. If keeping left/right separation matters, AMR is the wrong target; convert your AU to MP3 or WAV, which both preserve stereo.
Is AMR a good format for archiving my AU recordings?
No. AMR-NB is a lossy, narrowband speech codec, so archiving to it permanently throws away fidelity you cannot recover. Use AMR only for delivery to phones, MMS, or .3gp workflows. For a long-term master, keep the original AU or convert to a lossless format such as WAV or FLAC.