David, I should point out, if others haven't already done so, that dynamics in music doesn't mean just volume. It also encompasses other things such as timbre, tempo, rhythm - all techniques available to the performer. If you look at some of the pieces in Jim Copper's songbook, for example, there are written changes of time signature. You might get a 5/4 or a 3/4 bar popping up in the middle of a piece essentially in 4/4. This doesn't mean that the singers were consciously singing those time signatures as an exercise in dynamics; merely that Jim was indicating a subtle change of rhythm - one which the singers used naturally and unselfconsciously. But they were still there. The dynamics of a song or tune refers to the total shape of the song or tune, and there can be very few performers in any genre who sing or play in a dead monotone with no light and shade.