Hi guys!
As far as I know the pitch fork is the only acoustic sound source that can produce
a single note without any overtones. Which means it has no timbre. I'd say
most people make a difference between keys without noticing it. The better your pitch
is the more subtle a difference is noticed An unschooled listener hears a difference at, I guess,
about a third. A schooled one a full step and a selected few a half step or less(yes semitones).
What I'm trying to say is that as well as there is a difference between a note and its
sub octave we are not without blame. Our hearing is not evolutionary made for
listening to music. It just works really well for it and so music as we know it originated.
So back to your question. What that has been written is mostly about the old modal
scales in ancient Greece. They were said to have different effects on the listener. Preparing
one to go to war for an example. But that is scales and its a whole different story.
Transposing a song from C major to D major will never be without practical difference but in theory
not so much. But since theory is a later construction it already had its framework lined out.
And, as other contributors of this thread already stated, all (acoustic) instruments sound different
in different keys. This basically because they are in one way or another constructed, and not always
with intention, that way.
I'll end here otherwise I'll go on forever.
My best to all of you,
- Martin