What an AU file is and why you might need one

An AU file is an audio format that stores sound in a way that older computers and some specialized equipment still recognize. It was developed by Sun Microsystems in the 1980s and remains common in Unix systems, some web browsers, and older voicemail or phone systems. If someone asks you to send audio in AU format, they usually need it because their equipment or software only reads that particular format.

Creating an AU file means taking audio you already have — a recording, a music file, a voice memo — and converting it to the AU format. You do not need special equipment or technical knowledge. The process uses free software that runs on Windows, Mac, or Linux.

The most straightforward way is to use Audacity, a free audio editor that works on all three operating systems. Audacity can open almost any audio file you have and save it as AU format in about three steps.

Key Takeaways

  • AU is an older audio format still used by some phone systems, Unix computers, and legacy software that does not read modern formats like MP3 or WAV.
  • Audacity is free software that runs on Windows, Mac, and Linux and can convert any audio file to AU format in minutes.
  • You need the audio file you want to convert, Audacity installed on your computer, and about five minutes to complete the process.
  • AU files are smaller than some other formats, which is why older systems still prefer them, but modern software rarely asks for them unless you are working with specialized equipment.

read and install Audacity

Go to audacityteam.org in your web browser. Click the large blue "read" button in the center of the page. The site detects your operating system automatically and offers the right version for Windows, Mac, or Linux.

Once the read finishes, open the installer file. On Windows, double-click the .exe file. On Mac, drag the Audacity icon into your Applications folder. On Linux, follow the instructions for your distribution. The installation takes less than a minute and does not require any choices — just click through the prompts.

Open Audacity after installation. You will see a blank workspace with a toolbar at the top and an empty area below. This is where your audio will appear once you open a file.

Open your audio file in Audacity

Click File in the top menu, then click Open. A window appears showing your computer's folders. Navigate to wherever your audio file is stored — usually your Downloads folder, Documents folder, or Desktop.

Click the audio file once to select it. Audacity reads MP3, WAV, FLAC, OGG, M4A, and many other formats. The file name appears highlighted in blue. Click the Open button at the bottom right of the window.

Audacity loads the file and displays it as a waveform — a visual representation of the sound. You will see a blue or colored wave pattern in the main workspace. This can take a few seconds for longer files. Do not close the window while it loads.

Save the file as AU format

Once the waveform appears, click File in the top menu again. This time, click Export, then click Export Audio. A save dialog opens.

At the bottom of the dialog, you will see a dropdown menu that says "WAV (Microsoft) signed 16-bit PCM" or another format name. Click that dropdown. Scroll down the list until you see AU (Sun Au). Click it to select it.

At the top of the dialog, type a name for your file in the text box. You can name it anything — for example, "voicemail" or "recording". Do not add the .au extension yourself; Audacity adds it automatically.

Choose where to save the file using the folder list on the left side of the dialog. Your Desktop or Documents folder is usually easiest to find later. Click the Export button at the bottom right.

Handle the metadata dialog if it appears

After you click Export, Audacity may show a small window asking about metadata — information like the song title, artist name, and other details. For most AU files, you can leave these blank. Click OK or Export at the bottom of this window.

The file saves when ready. Audacity returns to the main window with your waveform still visible. Your AU file now exists in the folder you chose. You can close Audacity if you are finished.

Verify your AU file was created

Open the folder where you saved the file — your Desktop, Documents, or Downloads folder. Look for a file with the name you typed, followed by .au. For example, if you named it "voicemail", the file will be called "voicemail.au".

Right-click the file (or Control-click on Mac) and select Properties on Windows or Get Info on Mac. A window shows the file size and confirms the file type as "AU Audio File" or similar. This confirms the conversion worked.

You can now send this file to whoever requested it, or use it with equipment that reads AU format. The file is ready to use.

What to do if you need to edit the audio before saving

Audacity lets you trim, cut, or adjust the audio before you save it as AU format. After you open your audio file, you can select a portion of the waveform by clicking and dragging across it. The selected area turns lighter in color.

Click Edit in the top menu to see options like Delete, Trim Audio, or Silence Audio. You can also adjust volume by clicking Effect and choosing Normalize or Amplify. Make your changes, then follow the save steps above to export as AU format.

If you make a mistake, click Edit and then Undo to reverse the last action. You can undo multiple steps by clicking Undo repeatedly.

Frequently Asked Questions

Can I convert an AU file back to MP3 or WAV?

Yes. Open the AU file in Audacity the same way you opened your original audio file. Click File, then Export Audio. In the format dropdown, select MP3, WAV, or another format you need. Click Export and choose where to save it. The process is identical to creating an AU file.

Why is my AU file so much smaller than the original MP3?

AU format uses older compression methods that create smaller files than modern formats like MP3. This is why older systems prefer AU — it saves storage space on equipment with limited memory. The trade-off is that AU files may sound slightly lower quality on modern speakers, though most people do not notice the difference.

What if Audacity will not open my audio file?

Audacity reads most common formats, but some proprietary or very new formats may not work. Try converting your file to MP3 or WAV first using online conversion tools or your phone's built-in tools, then open that converted file in Audacity. You can also check the Audacity documentation at audacityteam.org for a complete list of supported formats.

Do I need to install anything else besides Audacity?

Audacity works on its own for most formats. If you want to export as MP3, Audacity may ask you to read an additional library called LAME the first time you export to MP3. Click the link Audacity provides and follow the installation steps. For AU format, no additional software is needed.

Can I create an AU file on my phone?

Audacity does not have a phone version. On iPhone, you can record audio using the Voice Memos app, then use a file conversion app from the App Store to convert to AU format. On Android, record using the built-in Recorder app, then use a conversion app. Search your app store for "audio converter" to find options.