1
general::
Produce something loudly or hastily by striking, either a musical instrument or a typing keyboard. For example, The accompanist banged out the melody on the piano, or John planned to bang out his presentation in a couple of hours. [Late 1800s]
American Heritage Idioms
2
general::
Phrase(s): bang something out
to play something on the piano, loudly, banging on the keys; to type something on a keyboard by pounding on the keys. • Let me bang this melody out and see if you can guess who wrote it. • Please bang out the school song good and loud. • I banged out the newspaper story and just barely made my deadline.
McGrawhill's American Idioms And Phrasal Verbs