to fit the instruments that will be playing the piece
One reason certain key signatures are used is to fit the instruments that will be playing the piece. When composing or arranging music, one important consideration is the range and capabilities of the instruments that will be performing the piece. Different instruments have different ranges and tonal qualities, and certain key signatures may be more suitable for particular instruments. For example, wind instruments often have a limited range and certain keys may provide better fingerings or breath control for the players. Additionally, certain key signatures may better suit the timbre or resonance of certain instrument families, such as the bright and brilliant sound of brass instruments in keys like B-flat or E-flat. By selecting a key signature that fits the instruments well, composers and arrangers can ensure that the music is playable and sounds its best when performed.
One reason certain key signatures are used is to fit the instruments that will be playing the piece. Different instruments have different natural ranges and tonal qualities, and using a specific key signature can help ensure that the piece is playable and sounds good on those instruments. For example, if a piece is written for a trumpet, using a key signature that is comfortable for a trumpet player, such as B-flat or C, can make the piece easier to play and more suited to the instrument's tonal qualities.
