Advanced Audio Coding (AAC) is a lossy format used for compressed audio files that was intended to replace the MP3 format. AAC is a standard within the MPEG-4 (MP4) specification, and as such, some AAC encoders give the filename an extension of MP4 or M4A versus AAC. The AAC format is believed to result in better quality audio files as compared to MP3 files of the same bit-rate, and is the format used by Apple® Inc., Nokia® and other manufacturers of portable electronics. For all of these reasons, people often want to convert uncompressed audio files like WAV to AAC (MP4/M4A), rather than to MP3.
For PC and Mac® users who have iTunes® installed, the built-in AAC encoder can be used to generate AAC files, though the M4A extension will be assigned. Navigate to the Preferences menu inside iTunes® then click on the Import Settings button. Next to "Import Using" choose the AAC encoder from the drop-down menu, then click OK. Now add the WAV file to the library, or add a folder of WAV files. Right-click on the song(s) and choose Create AAC version from the popup menu. The AAC files are created in the standard Music folder, under the iTunes® subfolders, with an extension of M4A.
For PC users who do not have iTunes® installed, there is a handy little audio encoder called BonkEnc© Audio Encoder by Robert Kausch. This program is free and includes several encoders for converting many types of audio files. To convert WAV to AAC open BonkEnc© and go to Options, General Settings, then choose the "FAAC MP4/AAC Encoder" from drop-down list of encoders. Next click the Configure Encoder button, and the Format tab. Here you can choose the file format of AAC or MP4, allowing you to generate files with an actual AAC extension. You can also tick a box to allow ID3 tags to be embedded. Add your WAV file(s) and click the arrow icon to generate the AAC files.
For those who already have Audacity© installed on their computers, it can also convert WAV to AAC though like iTunes®, it assigns the M4A extension. Audacity© is an open-source, free, cross-platform sound editor and conversion tool. To create an AAC file, open the WAV file inside Audacity© then choose File, Export and under Save As File Type, choose "M4A (AAC) Files (FFmpeg)" from the drop-down menu. Click the Options button to set the quality as desired. Click Save and a popup will allow you to edit ID3 tags before the AAC/M4A file is generated.
Note that Audacity© uses plugins to do its conversions. If the plugins are not installed you will receive an error. To get the plugins, open Audacity© and go to Edit, Preferences, then highlight Libraries in the navigation tree at left. On the right will be a button to download an MP3 encoder (LAME), and a button to download an AAC encoder (FFMPEG Library). Clicking the Download buttons will take you to a page of instructions for all platforms, and direct links for the plugins. Once done, this program provides a quick, easy way to convert WAV to AAC files (with M4A extensions).
There are also many other conversion tools that can take your files from WAV to AAC in both freeware and shareware flavors. Some MP3 players might not recognize AAC files, though compatibility is common in newer players.