Keys of the Well-Tempered Clavier

I'm new to music theory and the keys music is written in, so please bear with me!

When "Happy Birthday" is sung, the person who starts the song picks a key and everybody joins in and follows along, and nobody is any wiser about they key signature. First, is this true, or are they just picking a pitch that may not be A440?

If that is basically true then when Bach wrote the Well Tempered Clavier in each key for both Books... If all his music was transposed to C Major or Minor, would it make a difference? If he shifted every piece by a half tone would his work have been less influential or enjoyable? I've had a hard time trying to Google an answer. Somebody once wrote that the timbre would be different because of the way the piano was designed. That sounds like a plausible reason to pick a specific key for the piano if you are that sensitive, but does that mean if we played a synthesizer with pure sine waves, the key wouldn't make a difference?

With respect to WTC, this topic has been debated for some time. The same question was asked by Glenn Gould re Bach's various suites (and if substitution of a middle movement from one, proper transposed, into another of the same type of dance.) Because we do no know for sure what temperament (or even what pitch) Bach used for sure, people debate these questions passionately.

I see, so that goes back to temperament, and it sounds like what Bach played is probably not what we hear today because our pianos are tuned equal tempered. Either way, Bach only had organs and harpsichords, so he'd probably be intrigued by what he'd hear today with our modern iron framed pianos and all these years tweaking scale design. So that debate is will probably never be settled, and to me it's interesting but not the part of music theory that I'm trying to sort out.

I'm starting to understand key a little bit more and have read some articles about stretch tuning on a piano, but honestly, I have a hard time hearing the difference between temperaments, let alone the smaller tweaks done for stretch tuning, so let me frame my questions in the context of having no timbre and tuning effects to deal with to confuse the situation.

So, if you're going to write a piece that changes key by more than a few half steps, maybe you want to start between D4 and G4, so you don't end up on D3 for the majority of your tune, if you had started in the key of C at C4. Is that something a composer objectively thinks about?

I've read people mentioning that some keys are associated with some different emotions (if we exclude timbre again), could it be that they are also inadvertently starting in a differ mode at the same key as well, i.e. Dorian (C major) vs Aeolian (A Minor)? I guess I'm going off topic, but to me, it's the same question. Maybe they can play faster in some key signatures?



Edited 1 time(s). Last edit at 06/16/2018 08:03PM by k. (view changes)