Transcription is the act of writing pre-existing music into a notated form. Since most popular music is not written down, transcription often plays an essential role in copyright disputes. By rendering the music into a notated form, one is more easily able to analyze the principal musical features—melody, harmony, rhythm, form, instrumentation—of the work(s) in question.
Transcription usually requires well developed musical training and a good ear, since the transcriber is most often required to proceed only on the basis of the sound source, with little additional notated information. Thus one often sees transcriptions done by expert witnesses in copyright cases.
Transcription is distinct from arrangement. The latter term describes an adaptation of music intended for one set of performing forces to another. In transcription, on the other hand, one is merely writing down what one hears. Transcription might serve as a starting point for an arrangement. In the context of a copyright dispute, however, transcription is most often used for an analytical purpose.