key transposition

I'm surprised nobody's made a Derek Smalls "saddest of all keys" reference yet.

The range of the specific instrument is important, because transposing affects a number of elements like hand position, harmonic content, level of energy required, et cetera (minor things, mainly, but I'm sure it all adds up). And the flexibility of the instrument itself is a definite factor- a flute (for example) playing at the extreme high or low end of its range will add a dramatically different character than one that is comfortably centered.

Also, never underestimate the importance of experience- you hear enough sad songs in F#m when you're young and that will always seem like an intrinsically sad key to you, even if you don't consciously make the distinction. Minor is almost universally considered 'sadder' than major, when the only difference is a lowered 3rd (well, depending on the mode, I mean). Is that a natural distinction or just association?

But I think there is something, maybe even at the neural level, that responds differently to different keys. Of course, the keys themselves are an artificial human construction...so it must be specific combinations of wavelengths and timbres that produce the effect. Perhaps music software of the future will provide composition based on desired combinations of mood-affecting fundamental tones.

Of course I understand that the intervalic relationship between notes is supported by mathematical ratios.

I'm saying that the keys themselves were created to facilitate understanding of musical principles. There is no Db harmonic minor scale in nature; there are only various wavelengths that compliment each other in a musical sense better than others.

An inch does not have any real meaning before you make a ruler to measure it...no matter how specific you are about how many of them go into a yard. 440hz is not naturally any less of a 'real note' than 442hz, or 438hz, so therefore the keys and scales (deriving from the fundamental note) are based on human standards.

On an instrument without set temperament, one can transpose a song by minute amounts, and sooner or later it's going to have an effect on the overall sense of the piece.