To convert an audio file in MP3 format to the AAC format that the iTunes Store and iPods use by default, download and install Any Audio Converter, add the MP3 files, select the AAC format as the output solution, and start the conversion process. Converting MP3 files to the AAC format is not necessary since iPods can reproduce MP3 audio files without problems, as of 2015.
Go to Any-Audio-Converter.com, and click on the Free Download button on the home page. Double-click on the executable setup file after it finishes downloading, select the destination folder, and complete the installation process. Start Any Audio Converter via the shortcut that the installation places on the desktop, or open it through the Start menu. Click on the Add CD Disc button to add MP3 files directly from a disc, or drag the audio files to the main screen.
Open the drop-down menu, access the Common Audio Formats section by clicking on the music note icon, and select the AAC option. Choose the level of conversion quality in the Basic Settings section to control the file size, access the Audio Options section, and configure the parameters such as audio codec, audio bitrate and the number of audio channels as desired. When ready, click on the Convert Now button, and locate the AAC files by right-clicking on the audio files in the main screen and selecting the Open Destination File Location option.