From the File menu, choose Convert to open the MusicMatch File Format Conversion screen. From this screen you can convert .aiff files to .mp3 files.
From Source Data Type at the bottom/left of the conversion screen, specify the format of the files you wish to convert; either MP3, Windows Media or WAV.
From Source Directory at the top/left of the screen, browse for the location of the source file. Select the file(s) you would like to convert from Highlight Files to Convert in the middle/left, by clicking on it. You may select all files in the directory by choosing Select All at the bottom left. To deselect files, choose Select None.
Determine what directory the converted file will be saved to from Destination Directory at the top/right.
The Destination Data Type options, on the bottom/right, will change depending on the Source Data Type. If your source files are .mp3 files, the Destination Data Type will default to WAV. If your source files are .wav files, the Destination Data Type will default to MP3 128 kbps. When converting to MP3, you may also opt to convert at 96 kbps, 64 kbps or 32 kbps. The lower the compression rate, (in kbps) the smaller the resulting .mp3 file. See Record Settings for more information on compression rates.
In the bottom/right corner, click the Start button. A converting file dialog will be seen allowing you to view the conversion progress.
The newly created .mp3 file(s) can be seen in Converted File Names on the middle/right.