what are the musical instruments used to play the background of that track?
saxophone
Shake It Off
 Swift's vocal range spans two octaves from G to G. Swift semi-raps in the bridge. The song's arrangement features a saxophone.
who wrote shake it off by taylor swift Taylor Swift, Max Martin and Shellback. who is this second person mentioned? Karl Martin Sandberg, known professionally as Max Martin, is a Swedish singer, songwriter, and record producer what other bands/singers has he worked with? Britney Spears' when was that track released? August 18, 2014
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Shake It Off [SEP] Composition
"Shake It Off" was written by Swift, Martin and Shellback. Produced by Martin and Shellback, the song's duration is three minutes and thirty-nine seconds. Musically, "Shake It Off" is an uptempo dance-pop song written in the key of G major at tempo of 160 beats per minute, and exists outside of the traditional country pop musical style of Swift's previous releases. Swift's vocal range spans two octaves from G to G. Swift semi-raps in the bridge. The song's arrangement features a saxophone. Jason Lipshutz from "Billboard" compared the song's melody to that of Macklemore & Ryan Lewis' song "Thrift Shop" (2013).