AMR to AU Converter

AMR to AU Converter

AMR (.amr) is a narrowband speech codec built for mobile voice recordings, while AU (.au, also called .snd) is one of the oldest digital audio containers — Sun Microsystems' format for Unix workstations and early Java audio. This converter transcodes a low-bitrate AMR voice clip into the legacy AU container, which is useful mainly for old Unix tooling, Java applets, or telephony pipelines that still expect μ-law .au input.

Both formats are 8 kHz, telephone-grade audio, so this is a like-for-like legacy transcode. AMR is lossy and already discarded everything outside the 200–3400 Hz speech band, so converting to AU cannot add fidelity that was never recorded. If you only need a clip that plays everywhere, convert AMR to MP3 instead; for a standard uncompressed file, convert AMR to WAV.

AMR Format at a Glance

AU Format at a Glance

How to Convert AMR to AU

1. Upload Your AMR File: Drag and drop your .amr recording onto the page or click "Add Files" to select one or more files.
2. Set the Audio Sample Rate: Leave it on "Original" to keep the 8 kHz speech rate (recommended for μ-law AU); changing it only resamples, it cannot add detail AMR never captured.
3. Set Audio Channel and Trim (Optional): Keep channels on "Original" (AMR is mono), and use Trim if you only need part of the clip.
4. Convert and Download: Click "Convert" and download your .au file. Files are uploaded over an encrypted connection, processed on our servers, and deleted automatically after a few hours — no sign-up, no watermark.

Frequently Asked Questions

Will converting AMR to AU improve the audio quality?

No. AMR-NB is a lossy speech codec that only captures the 200–3400 Hz voice band at 8 kHz. AU is just a container — it stores whatever you put in it but cannot reconstruct frequencies AMR already discarded. A μ-law AU output stays telephone-grade; a PCM AU output makes the file larger without adding real detail.

What encoding does the AU output use?

By default, AU is most commonly written as 8-bit G.711 μ-law at 8 kHz — the same telephone-grade companding the format was built around, which keeps the file small and matches AMR's 8 kHz origin. AU can also hold G.711 A-law or 8/16/24/32-bit linear PCM if your target system needs uncompressed samples.

What programs can open an AU file?

AU is a legacy Unix format, so support is uneven on modern desktops. Audacity, VLC, and FFmpeg-based players open .au files; Java's javax.sound libraries read them natively. Many consumer apps and phones do not, which is why MP3 or WAV are better choices for everyday playback.

Why would I convert to AU instead of MP3 or WAV?

Mainly compatibility with old software. If a Unix utility, a Java applet, or a telephony pipeline specifically expects .au (μ-law) input, this conversion gives it the right container. For anything else, AMR to MP3 is far more universal and AMR to WAV is a more standard uncompressed option.

Is the AU output a μ-law or PCM file, and why does it matter?

It matters for size and compatibility. μ-law AU packs roughly 16 bits of dynamic range into 8 bits, so it stays at about 8 KB per second — small, telephone-quality, and what most legacy .au consumers expect. Linear PCM AU is uncompressed and larger, but since the source is narrowband AMR, the extra bytes carry no extra fidelity.

Does this conversion keep the original AMR sample rate?

Yes, when you leave Audio Sample Rate on "Original" the 8 kHz narrowband rate is preserved, which is the natural match for μ-law AU. In our testing, a one-minute AMR voice memo converted to default μ-law AU produced a file of roughly 0.5 MB — close to the ~8 KB/s μ-law rate — while choosing 16-bit PCM at the same 8 kHz roughly doubled it without adding audible detail.

Are my files private during conversion?

Yes. Files are 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.