By default, iTunes downloads music in with an .m4a extension. You can ensure you're getting the best quality (typically 256 kbps ) by checking your preferences. On PC: Go to Edit > Preferences > Downloads . On Mac: Go to Music > Settings > Playback .

Go to Edit > Preferences > General > Import Settings . Choose Encoder: Set "Import Using" to AAC Encoder .

Once your settings are correct, you can download your library: