temperament - its effect on a key

1. What are the keys of temperament?
2. What does equal temperament mean in music?
3. What's the saddest key in music?
4. What is an unequal temperament?

What are the keys of temperament?

"Temperament refers to the various tuning systems for the subdivision of the octave," the four principal tuning systems being Pythagorean tuning, just intonation, mean-tone temperament, and equal temperament.

What does equal temperament mean in music?

Equal temperament, in music, a tuning system in which the octave is divided into 12 semitones of equal size.

What's the saddest key in music?

D minor, wrote Schubart, is a key of “melancholy womanliness, the spleen and humours brood.” He actually found D#minor to be sadder. It is the key, he wrote “of brooding despair, of blackest depresssion, of the most gloomy condition of the soul.” There are also many famous songs in D minor.

What is an unequal temperament?

: a temperament that keeps pure or nearly pure intonation in some keys and accumulates the dissonances in the little-used keys.