Here Richard examines how the composer can assure the score will be mixed at a reasonable volume. In order for music to do its job, it must be heard.
It will only be heard if the composer successfully avoids the sonic competition presented by other audio elements in the mix.
Sonic Competition - Spanish Subtitles
From The Richard Bellis Masters Series
1280 x 720 H.264 MPEG-4 ~ 551 MB