Aspiring songwriters came to demonstrate tunes they hoped to sell. When tunes were purchased from unknowns with no previous hits, the name of someone with the firm was often added as co-composer (in order to keep a higher percentage of royalties within the firm), or all rights to the song were purchased outright for a flat fee (including rights to put someone else's name on the sheet music as the composer). An extraordinary number of Jewish East European immigrants became the music publishers and songwriters on Tin Pan Alley – the most famous being Irving Berlin. Songwriters who became established producers of successful songs were hired to be on the staff of the music houses.