Think of an arranger as one of those $89 toys from the Mart. It plays beats and cool sounds and lights up and...

As you get further up the arranger food chain, things get more and more sophisticated; sounds get closer to and sometimes exactly as the high-end synths. Beats are more realitic and sound real. Backing rhythm chords and stabs are top-notch. Other features make the art of making music simpler and more realistic. Arrangers can help you create a song idea or record an entire piece.

Arranger - the vehicle for putting musical parts together into a cohesive unit. In this case it's a machine, not a person.