> I suppose it’s possible to change the sound of an entire piece of music just by changing the key signature, but does anyone actually do that? Much more interestingly, this touches on the reason why different pieces were given keys at all by their composers (think "foo in B flat minor by Chopin"). Musical instruments have to be tuned to a particular key. This is because of the frequency ratios: the circle of fifths…
Is that true? I thought most instruments (or at least most pianos) these days were tuned to be equal tempered, so each scale would sound the same (modulo a pitch scaling).
Otherwise, you're right. Historic tunings often tried to optimize for a certain base scale (often times C major), while leaving behind a really bad sounding tuning at the other side of the circle of fifths ( https://en.wikipedia.org/wiki/Wolf_interval ).
Modern pianos are usually equal tempered, which is the strategy of leaving every scale equally bad off - but on the other hand being able to play in all keys without sounding too bad (The famous "well-tempered piano" is referring to this historic change in tuning strategies with small pieces written in all different kinds of keys, all of which would have sounded weird before).
The more I learned about tuning, the more complex, beautiful and sad this topic became for me: http://blogs.scientificamerican.com/roots-of-unity/the-sadde...
It's fascinating and even a little philosophical that we can get so close to perfection with the 12 step tuning - but never, ever completely attain it.
By the way - That's part of the reason why choirs and orchestras often sound so good: As most other non-fixed-string instruments are able to do a slight adjustment in pitch, they can actually play perfect intervals in any chord, dynamically adjusting to any scale.