To cite a song downloaded online and listened to through an app like iTunes, follow the MLA template of core elements.
List the name of the performer and the title of the song. Then provide any additional elements provided by the source, including the name of the record label as the publisher and the song’s release date:
U2. “You’re the Best Thing about Me.” Island Records, 2017.
If the song is from a collection, list the album title in the “Title of container” slot:
Belle and Sebastian. “The Model.” Fold Your Hands Child, You Walk Like a Peasant, Matador, 2000.
The publication details displayed will depend on the software and may be incomplete (e.g., the mobile app for iTunes may display different information than the desktop app), and you may need to consult other reliable sources (e.g., the iTunes Store site) to supply as much of the missing information as you can.
App as Version
The fact that you download a song from a particular Web site to listen to on a personal device does not need to be accounted for in your citation. The software application that you use to listen to the song is also generally not necessary to specify in your entry, but you can electively include it in the “Version” slot:
U2. “You’re the Best Thing about Me.” iTunes app, Island Records, 2017.
Other Uses of the Version Slot
If a specific version of the album is specified, list it along with the name of the app in the “Version” slot:
Sleater-Kinney. “The Fox.” The Woods, bonus track version, iTunes app, Sub Pop Records, 2005.
If the source provides the original date of the song as well as the date it was subsequently released in a collection, list the original song date in the optional-element slot after the title:
Gaye, Marvin. “Can I Get a Witness.” 1963. The Very Best of Marvin Gaye, Motown, 2001.
Sometimes, the file format might be important to know–for example, in a paper on the musical quality of a recording. In such cases, list the file format in the optional-element slot at the end of the entry:
Some Band. “Demo Recording of Track 1.” Mastered by DL Studios, 2017. WAV file.