I will try my hand at explaining this. I have a pretty good grasp on the differences, but explaining them? HA. That's a whole other story
But I think it might help to sort of lay them out in a linear fashion..
Song - Your typical vocal song - we all know what this is, right? Song structure, lyrical vocal is the main focus.
Muzak - Same exact song, exact replace the lyrical vocal with an instrument. This often sounds super cheesy, but has it's place in the licensing world.
Instrumental - Same structure as the previous two (see song structures), however the melody is NOT maintained throughout with one instrument like muzak. It will often be a combination of lead sounds using call and response, more sparse melodies, lots of ear candy (cool and interesting sounds that help maintain interest without being too frenetic or distracting), or other elements to keep things moving forward. These will also have typical song length (3-5 minutes).
Cue - Unlike the previous 3, the cue does NOT follow song structure. The cue has a very distinct job to do. That's right, it is providing a service. It is not created for entertainment value, like the previous 3. A cue is written to support ONE mood, with generally ONE main melodic idea. Depending on the style, a cue ranges from 90 seconds (1:30) to 3 minutes. 2:00-2:30 seems to be the most common length I have seen. A cue GENERALLY is built in 4-8 bar sections. I.E. every 4-8 bars something is changing. This can be a number of things: adding/subtracting layers, add/remove melodies and harmonies, risers, transition fx, etc etc. As mentioned above a cue will typically have an AAA or AABA structure, or some variation of that. I think it helps when cue writing to remember that you are NOT trying to impress anyone. You are NOT trying to show off your abilities or how great of a composer or producer you are. However you ARE providing a service. Your goal is to make a piece of music that supports one mood/emotion very well, a piece of music that walks the line between being simple enough to not distract, but interesting enough to fit in with the style and quality of the show. I could go on, but I think (hope) I've cleared it up a little bit. As stated by a very prolific music supervisor at the road rally - "I don't want the best music, I want the RIGHT music." and - "you are in the film/tv industry, not the music industry." I think just understanding that - that you are just a small part of the puzzle providing a service for the greater (film/tv) industry, that helps you write more accurately and appropriately, which will lead to more success and more placements.
If you have not yet, I HIGHLY recommend purchasing Dean's Books (Demystifying the Cue, Demystifying the Genre, and Write, Submit Forget Repeat). Also Steve Barden just put out a book too, although I can't technically vouch for that one as it's still next on my list to read, I've already heard wonderful things about it and can't wait to dig in.
Demystifying the Genre also comes with audio examples, which are open to the public. Maybe go through and check these out, and you will very quickly see how cues are structured and how they function. All of these cues, to the best of knowledge, have earned many placements.
https://soundcloud.com/all-screen-music
Sorry for the length, but hopefully that helps!!
