 In April 1926, Warners signed a contract with AT&T for exclusive use of its film sound technology for the redubbed Vitaphone operation, leading to the production of "Don Juan" and its accompanying shorts over the following months.During the period when Vitaphone had exclusive access to the patents, the fidelity of recordings made for Warners films was markedly superior to those made for the company's sound-on-film competitors.Meanwhile, Bell Labs—the new name for the AT&T research operation—was working at a furious pace on sophisticated sound amplification technology that would allow recordings to be played back over loudspeakers at theater-filling volume.