George Groves is credited as being the first production sound mixer. He worked in New York in 1925 for Western Electric and later Warner Brothers and recorded on the "Vitaphone" (a disc recorder in the phonographic sense). Recording at Vitograph Studios in Brooklyn was problematic due to subway noise and pigeons (the latter dealt with using a large pole, the former - well, you know how it is), and so production was moved to the Manhattan Opera House, where they experienced a different noise problem:

When Reinald Werrenrath was to be recorded in a woodland setting, a resourceful member of the technical staff brought in a boxful of field crickets for sound effects and some of them escaped. Entomological note: crickets are difficult to locate and sing loudest when the director says 'Quiet'!

For a lot more on the redoubtable George Groves, check out http://www.georgegroves.org.uk/, a fantastic online tribute with anecdotes, pictures, media clips, and more.

Below: The set of La Fiesta (1926) at the Manhattan Opera House. George Grove mixed it from six floors above with cables wired through the ventilation system. Click the picture for more information on this impressive rig.