What are you talking about here.
what do you call one of those bits/threads of music?
Do you mean like the "components" of a song, which would be multi-track. They call them "song stems".
You mention classical. I ran out of riff combinations years ago so been "borrowing" public domain classical for melody notes. I've dealt with classical for the past 5 years putting together my first album. So know a little bit about what goes on with classical.
Sometimes a dude over there is only playing some notes of a chord. Some other dude is playing the other notes to complete the chord. Might be more people than that to complete a chord. If you solo one guy, it'll only be half of a chord.
So no kidding,
Each bit, if played on its own, might sound weird
The other day I was wanting to test out speeding up the tempo of some solo hip-hop rapping but leave the pitch normal, so he wouldn't sound like a chipmunk. Then it would sound like he was rapping fast like Eminem. I don't rap, so looked around for some kind of multi-track, hip-hop stems, found one page with some.
Searching google for hip-hop multitrack stems, wind up at this forum:
Then somebody commented there:
"I posted this in a thread a week or so ago. in case you didn't see it."
"The 'Mixing Secrets' Free Multitrack Download Library (Cambridge Music Technology). This is from the guy who wrote the book "Mixing Secrets for the Small Studio"
That link goes to this page:
http://www.cambridge-mt.com/ms-mtk.htm
"The 'Mixing Secrets' Free Multitrack Download Library"
Now, you scroll down.. there's various genres. Beside each is links to a zip file for the multi-track wav files. You could download those and at least hear separate wav files to get an idea of how they construct song components.
If you had a multi-track recording DAW program, (digital audio workstation), you could import all of those wav files which would then all play together at the same start time, and re-create the final mix song. Now you get an idea of how these songs are made by soloing whatever individual tracks.