Thanks for that dismissal Mathis. I do think of technical questions all the time and precisely this one often. What you do not think of is that artistic work can obliterate the significance of technicalities, and does so, on a regular basis. You can work all you want on your precious little technical problems and formants [*-)] but if you are dealing with a piece of crap artistically it doesn't matter. It is necessary not to have many things going on in the music that would distract from the dialogue, which is pretty obvious. I have heard scores by major composers that violated this. They are so concerned about their technicalities that they do not see the big picture which is that dialogue and music are already a two-part counterpoint. And so the music must be done with that in mind regardless of what register it is in. You could use a contrabassoon ensemble, or ten piccolos, and measure the frequencies, and their relative intensities blah-blah-blah Mr. Scientist and it still wouldn't matter because it all depends on what you do with the music artistically.
On Vertigo that is a good point, there is some use of underscoring. Though Hitchcock generally will pause the music for dialogue, I looked at Vertigo again with this question in mind, and notice two aspects of how the music is effectvely underscored, both of which are artistic, and not technical by the way -
1, the use of extremely simple chordal music, and 2, the continuation of a cue which has already been heard without dialogue, and continues underneath when dialogue starts. It is as if the audience hears it consciously at first, has "got it down" and so is not distracted as they are diverted into the dialogue.
