If we want to translate sound into digital format, or to translate digital information back into analog sound, we have to use a device called a transducer. Transducers translate one kind of energy into another. An audio transducer transforms sound waves in the air into some other form, such as an electrical signal.
Thomas Edison’s 1877 tinfoil phonograph was an early audio transducer. It converted sound energy into mechanical energy by translating the vibrations in air into grooves in a foil-wrapped cylinder. The owner of the phonograph inserted a stylus into a groove on the cylinder and then attached the stylus into a megaphone-type horn, reversing the direction of the transducer, and translating the grooves back into sound.
Some of today’s most common transducers include microphones, headphones, and speakers. They convert sound into electrical energy or vice versa.