What was the most important medium for Tin Pan Alley songs at the turn of the Century?

The most important medium for Tin Pan Alley songs at the turn of the century was sheet music. This format allowed composers and songwriters to publish and distribute their works widely, enabling amateur musicians to perform popular songs in homes and social settings. The rise of the phonograph later expanded the reach of these songs, but sheet music remained the primary vehicle for showcasing and promoting new music during this era.