Free online SPX to AU converter

SPX is an audio file format commonly used for speech recordings and compressed voice data, while AU is an older Sun/NeXT audio format that stores sound in a simple container and is often used for compatibility with legacy systems.

What is SPX?

SPX files are typically associated with Speex, a speech-focused audio codec designed for efficient voice compression. They are often used for recordings where small file size and intelligible speech matter more than high-fidelity music playback.

What is AU?

AU is a classic audio format originally used on Unix and Sun systems. It supports basic audio data and is recognized by many media tools, especially for older workflows and cross-platform compatibility.

How to convert SPX to AU

To convert SPX to AU, you need software that can decode the SPX audio stream and re-encode it into AU format. Because AU is a container format, the conversion usually involves selecting an audio codec and saving the output as .au.

The most reliable approach is to use a converter that supports both formats directly or a professional audio tool that can import SPX and export AU.

Best software for conversion

FFmpeg is the best overall choice for SPX to AU conversion because it is free, fast, and supports a huge range of audio formats. It works well from the command line and is ideal for batch conversion.

Example command:

ffmpeg -i input.spx output.au

If you prefer a graphical interface, Audacity can be a good option when the SPX file is supported through installed codecs or plugins, and it can export to compatible audio formats depending on your setup.

Conversion tips

• Check codec support before converting, since some SPX files may require specific decoder support.
• Preserve sample rate if you want the AU file to match the original speech quality.
• Use FFmpeg for batch jobs when converting multiple files at once.
• Verify playback after conversion, especially if the AU file will be used in legacy software.

Summary

SPX to AU conversion is straightforward when using a capable audio converter. For the best balance of speed, compatibility, and quality, FFmpeg is the recommended tool.