Free online AU to SPX converter
Convert legacy AU audio to speech-focused SPX with FFmpeg or 101convert.com
Convert AU to SPX online - free
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How to convert au to spx file
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Source format
AU is a simple audio file format originally associated with Sun Microsystems and early Unix systems. It is often used for basic uncompressed or lightly compressed audio, especially in older software, research tools, and legacy audio archives. AU files may contain mono or stereo sound and can use different encodings, but they are generally considered a legacy format today.
Target format
SPX is an audio file format commonly used for Speex-encoded speech audio. It is designed for voice recordings and other speech-focused content, offering good compression at relatively low bitrates. SPX is useful when you want to store spoken audio efficiently, such as voice notes, VoIP recordings, or archived speech clips.
How to perform the conversion
The most reliable way to convert AU to SPX is with FFmpeg, a widely used command-line multimedia tool that supports both formats.
- Install FFmpeg on your computer.
- Open a terminal or command prompt.
- Run a command like
ffmpeg -i input.au -c:a libspeex output.spx - If needed, adjust the audio quality or bitrate for speech, for example by adding
-ar 16000for a 16 kHz sample rate or-ab 24kfor a low speech bitrate. - Check the resulting
output.spxfile in a compatible player or editor.
If you prefer a simpler workflow, you can also convert the file on 101convert.com for free without installing any software.
In some cases, a two-step process may be useful: first convert AU to a standard intermediate format such as WAV, then encode that WAV to SPX. This can help if the AU file uses an unusual encoding.
Notes on quality and compatibility
SPX is optimized for speech, not music. If your AU file contains music or full-range audio, the conversion may sound noticeably worse than the original because Speex is designed for voice compression. For best results, use a mono source and a speech-friendly sample rate such as 8 kHz, 12 kHz, or 16 kHz.
Compatibility can also vary: some modern players support SPX directly, while others may require FFmpeg-based tools or specialized audio software. If you need broad playback support, consider keeping a copy in a more common format such as WAV or MP3 in addition to SPX.
Note: This au to spx conversion record is incomplete, must be verified, and may contain inaccuracies. Please vote below whether you found this information helpful or not.
AU vs SPX: format comparison
How the AU and SPX formats compare on the properties that matter most for this conversion.
| Property | .AU Sun/NeXT audio file | .SPX Speex |
|---|---|---|
| Compression | Uncompressed | Lossy |
| Audio quality | — | Medium |
| Metadata support | Basic | Basic |
| Streaming | Yes | Yes |
| DRM protection | No DRM | No DRM |
| Opens in a web browser | Partial | No |
| Typical file size | Large | Small |
| Open standard | Yes | Yes |
| Best used for | Speech and voice | Speech and voice |
| Introduced | 1988 | 2003 |
| Developer | Sun Microsystems / NeXT | Xiph.Org Foundation |
| MIME type | audio/basic | audio/speex |
Frequently asked questions
Is the AU to SPX converter free?
Yes, converting AU to SPX on 101convert.com is completely free. No registration, email address or installation is required.
How large can my AU file be?
You can upload AU files up to 1000 MB and convert up to 100 files at once in a single batch.
What happens to my uploaded files?
Files are processed automatically and deleted from our servers within a few minutes after conversion. We never view or share your files.
Do I need to install any software to convert AU to SPX?
No. The AU to SPX conversion runs entirely online in your browser and works on Windows, Mac, Linux, Android and iPhone.
Did the conversion fail?
In most cases, the cause is an incorrect file format. Please upload a valid AU file for this AU to SPX conversion. Occasionally, the issue may be on our side. We analyze recurring conversion failures and disable or fix the converter if we detect a defect.