Thank you, but I'm not sure if I explained myself correctly... I know that I can alter 'split' sections, but I meant more of a gradual adjustment.
You explained yourself quite clearly. Your are referring to iMovie HD and versions prior to them which had the "rubber band" audio track that you click on to add one or more little ball-like "handles" which could be independently adjusted to create continuous slopes and/or contours in the audio. Neither iMovie '08 nor '09 has this capability. You only have two options here. One is to divide clips into multiple segments each of which can have a different volume setting or you can apply alternative audio segments to force "ducking" of the main track. Segments can be as large or as small as you desire and can be used to "step" changes in the volume level. I did not mention the "ducking" option above because multiple "ducking" tracks can conflict with one another if/when overlapped. Depending on the reason you wish to modify the volume and whether or not there are other tracks of audio present, GarageBand may be a better place to manage multiple audio tracks since it has the continuous "rubber band" adjustments you want, as well as, individual volume controls for each track, a "master" volume control, left/right pan emphasis, and the ability to increase/decrease emphasis within a limited number of frequency ranges. Audio handling in iMovie itself remains rather basic while GarageBand is the place to do any "relatively" serious audio mixing.
