In harmony class one is taught not to use parallel perfect intervals as it undermines the independence of the voices. I have come to completely understand this and see why it is so important but when working with entire scores and lots of "voices" how do composers and arrangers stick by this rule?
Of course if you are doubling voices like a melody or bass part, each voice is no longer independent and this is done as a textural effect or to bring out melodic lines by doubling them at the octave etc. But are there other instances where parallel perfect intervals or other voice leading rules no longer matter and it is just about "filling out" the rest of the harmoni spectrum?
For example, I am currently working on a song where I started out with 4 part harmony and the texture is rather low. For the chorus of the song I want to include a piano part or guitar chops in the 5th octave to fill out the high end of the frequency spectrum and create more energy. I believe in the orchestra they call this "tutti" where everyone kind of joins in. How would a classical composer/ orchestrator have done this?
Would the higher piano chords (or higher woodwinds etc) be part of the voice leading in the sense that the lines would have to still have good voice leading. How is this possible? If you have 10 lines or more in the score are only some of those considered as part of the voice leading and the rest just given place in the various registers as "doubled" notes or did the classical composers treat each and every single line independently?
I find it hard to imagine how one might voice that higher piano part while still keeping all the voice leading rules in place. Maybe since the piano part is just part of the accompaniment it doesnt really matter if there are parallel 5ths or if there is parallel motion with the bass line. Or maybe not. Maybe those extra chords I want to use in the chorus still would sound much better adhering to some of the voice leading principles laid out in 4-part harmony. So which is it?