The main difference between a soprano and an alto saxophone is their size, range, and timbre.
A soprano saxophone is the smallest and highest-pitched member of the saxophone family. It is pitched in the key of B-flat and has a range that extends up to the altissimo register. The soprano saxophone has a bright and edgy tone that is often used in jazz and classical music.
An alto saxophone, on the other hand, is larger than a soprano saxophone but smaller than a tenor saxophone. It is pitched in the key of E-flat and has a range that extends from the low B-flat up to the high F. The alto saxophone has a warm and mellow tone that is often used in jazz, classical music, and pop music.
Overall, while both soprano and alto saxophones are in the higher-pitched range of the saxophone family, the soprano saxophone is smaller and has a brighter tone, while the alto saxophone is slightly larger and has a warmer tone.