Music as Slow Motion Device
Music can alter the perception of time quite heavily. It can actually even work like a subjective slow motion.
For example imagine a huge battle, the last few minutes of it, the hero is fighting, lots of fast action and instead of bringing in a busy action driven score which pushes forward we hear a slow, elegic, string carried legato piece. Even though we see the action still taking place in “real time” it feels like we are in slow motion just because of the music.
The same works the other way around. Examples can be heard an seen in many sneak scenes where the music pushes the tempo and increases the “stress” for the audience even though the images actually are quite slow. Such tempo alterations can have a fantastic effect and high emotional impact.