Free AU test files and sample generator
The classic .au/.snd uncompressed audio container. Generate valid .au sample files for testing audio players, converters and upload handling.
What is a .au file?
AU: Sun/NeXT Audio. The Sun/NeXT .au format is one of the oldest audio containers, with a compact big-endian header. It still turns up in Java's audio APIs and in legacy telephony systems.
Why generate a test AU file?
- Test legacy or Java audio handling.
- Verify a parser reads the big-endian header correctly.
- Check format detection across uncommon audio types.
What you can put inside a .au file
You get 4 content options for AU, so the file holds something meaningful rather than random padding: Silence, Tone (beep), Noise, Voice (synthetic). For AU these are alternatives, so choose the one that matches what you need to test.
How a .au file is identified
Every .au file begins with 2E 73 6E 64, ".snd". That is what a validator inspecting content rather than the file name looks for.
How the size lands on the exact byte
The header declares the data length, and the padding follows the audio it describes.
Negative testing with broken AU files
- Invalid. Identifiable, but wrong inside, so it fails during parsing.
- Corrupted. The leading bytes are destroyed, so the
2E 73 6E 64identifying a .au is gone. Same length as the valid file. - Incomplete. Truncated part-way, so it is genuinely shorter.
- Empty. Chosen under Content rather than File Condition: valid structure, no data.
Which failure to reach for, and what to assert for each, is covered in how to make a corrupted file for testing. For upload limits and type checks see testing file upload validation.
Sample AU content
[AU], .snd magic, 24-byte big-endian header, 8-bit PCM samples.
This shows the shape of the file. Your download is generated fresh at the size you choose, so the values will differ.
How to open and verify the file
Play in VLC or Audacity; inspect with `ffprobe file.au`.
Media type audio/basic · extension .au · category Audio
Generate a .au file → · questions about sizes, privacy or cost are answered on the site FAQ.
Frequently asked questions about AU files
What identifies a .au file?
A .au file begins with the bytes 2E 73 6E 64, ".snd". Those bytes are what a content-sniffing validator looks for, and what the Corrupted condition destroys.
How can a .au file be an exact number of bytes?
The header declares the data length, and the padding follows the audio it describes.
What can go inside the AU file?
There are 4 content options for .au: Silence, Tone (beep), Noise, Voice (synthetic). For AU these are alternatives, so pick the one matching what you need to test.
Can I download several broken AU files at once?
Yes, select more than one File Condition and you get one ZIP containing a .au per condition, each named after its condition.
Can the AU file use UTF-16 or a byte-order mark?
No, and deliberately. A .au file is a container rather than plain text, so rewriting its bytes as UTF-16 would not produce a UTF-16 document. It would produce a broken file. Use a text format such as CSV, JSON or XML for encoding tests.
How do I open or verify the AU file?
Play in VLC or Audacity; inspect with ffprobe file.au.