Over the last few decades, trailer music has become a genre in itself, with dedicated production studios such as Two Steps from Hell crossing over into the mainstream consciousness.
Trailer Music Structure
Vertical Composing is a term coined to describe the way many trailer tracks are structured. Essentially it means that instruments and sounds are gradually layered on top of one another as the piece progresses.
This is an art in itself, Hans Zimmer is the master at making his compositions sound 'huge' while still being musical. It's essential to make sure the frequency spectrum is nicely filled without resulting in a muddy mess. Trailer music usually has a three-act structure.
- Introduction - often moody and atmospheric will contain very subtle hints and motifs of what is to come.
- Middle - This section builds on the first, introducing more of the melody and increasing the dramatic tension.
- Finale and Ending - The is where all of the separate parts of the track come together, bring in the full melody, layer instruments to make it feel big and wide.
It's helpful - but not required - for music editors if there is a gap in between the sections, as several different pieces of music might be used in one trailer. Imagine each chapter as an individual track in its own right.
There aren't really any hard and fast rules on the length of the track, however, as a rough guide, it doesn't hurt to start out with each section lasting 30 seconds. Around 2:30 is the maximum to aim for.
You can also vary the structure creatively by adding percussion hits, or a few bars of sparse instrumentation in between the second and third acts. In my experience 'cold endings' are preferred. In other words, the track should build to a big finish and come to a full stop. Occasionally a softer ending might be requested, where the track still comes to a big climax but includes several seconds of lighter instrumentation as the credits roll.