A most critical audience, often numbering millions of people, lends careful ears to the synthetic sounds. The action of a radio play is as broad as that in a theater, and the faithfulness of the illusions depends largely upon synthetic sounds. An airplane engine, if picked up outdoors, would be heard for what it is. Inside a studio, the reverberations and echoes, clashing against the walls, would give the radio listener nothing but noise. But an old-fashioned foot pump organ makes a noise exactly like an airplane motor.
Hoof beats are hard to fake.
I almost considered bringing a horse into the studio and riding him myself, but he couldn't pass through the corridors. Hissing water is easily imitated by letting off compressed air. If a house collapses, a box of bricks are allowed to fall down a chute. A firecracker celebration on the rood gives the radio listener an idea that a battle is taking place. Machine guns are simulated by riveting machines.