It is helpful to know whether your volume is correct before exporting your recording to an MP3 file. There is a Nyquist plug-in for Audacity called ReplayGain which allows you to do this. It also provides a facility for Equal Loudness Normalization (ie for amplifying to the required level).
Important: first download the latest version of Audacity from this page. You may need to right-click on the link and select Save Link As. Save the file (called ReplayGain.ny) somewhere, then follow the relevant instructions below. It's important that you start with the latest version, as earlier versions used a different method of installing plug-ins. These instruction should work for Windows, Mac and Linux.
- In the Audacity Tools menu, select Nyquist Plug-in installer
- Browse to the place where you have saved ReplayGain.ny, and select it
Then, you need to enable the plug in:
- In the Tools menu, select Add/remove Plug-ins which will take you to the Manage Plug-ins window
- Select the New radio button
- Scroll down to ReplayGain, and click Enable. Then OK
You should find ReplayGain as one of the items under the Effect menu (towards the bottom, under the horizontal divider).
You mostly don't need to worry about where Audacity actually stores the plugin, but in case you are interested, it's here:
- Browse to the folder within This PC. in which Audacity is installed: it's probably under OS (C:), and within that Program Files (x86). There, you should find an Audacity folder at the top, or near it. In older versions of Windows you may need to look in C:\Program Files\Audacity or C:\Program Files (x86)
- Browse to the Plug-Ins subfolder.
User plugins are stored in ~/Library/Application Support/audacity/Plug-Ins.
Probably in somewhere like /home/USERNAME/.audacity-data/Plug-Ins). Note that .audacity-data is a hidden folder.
Using the plugin
The author explains use of the plugin in the Audacity forum here.
There is an explanatory video here.
N.B. Please be aware that this plug-in does not warn you if amplification will cause clipping when you Normalize. Check by View | Show Clipping and then View | Fit in Window. If red vertical lines are showing, this means that the audio has reached a level of volume where your voice may be distorted. If this happens, click Undo to undo the Normalization, and use the Effect | Amplify feature without the Allow Clipping box checked.
- More technical details for the ReplayGain plugin can be found here (the installation instructions are out of date).
- This official Audacity page gives more information on downloading and installing plugins generally.