In 1950, the guitarist and guitar maker Les Paul modified the head of his eight-track Ampex 300 to give it an extra recording head. This meant that for the first time, it was possible to do "sound on sound" dubbing. The advent of sound on sound dubbing opened the doors for over-dubbing, in which sounds are layer on top of each other. Without over-dubbing, the recording process would have been limited to one live take. Over-dubbing enables producers to add depth to sounds and enables musicians to correct mistakes from one take by playing the same part again in a new take.
Digital recording methods make it easier and faster to record, edit and mix recorded music. Digital interfaces give producers a visual representation of the sound waves that they have captured, enabling them to correct mistakes without the need for re-recording. The transition from analog to digital recording techniques made it possible for people to set up recording studios in their homes.
Musical Instrument Digital Interface, or "MIDI," was a joint collaboration between two companies, Sequential Circuits and Roland. Until 1982, synthesizers from different manufacturers were not compatible. MIDI serves as a universal interface for all MIDI-enabled equipment. Early applications were limited to hooking up synthesizers to various mixing consoles. Modern applications are far more versatile. MIDI acts as a carrier signal, which tells the computer what notes you are playing and at what velocity. The interface enables you to assign any sound to that carrier signal, effectively giving you an unlimited number of sonic options. MIDI also made the use of drum machines much more versatile in recording.
Auto Tune is an audio effect that can be used two ways. As a creative, sound-bending audio effect popular in Hip Hop and Pop music or as a corrective tool in the studio. The distinctive vocal sound on Cher's "Believe" is an example of Auto Tune used creatively, but it as a corrective tool that the effect is most valuable. Before Auto Tune, a singer would need to re-record parts of a vocal take if there were minor pitching errors. This added to the cost of the recording session and could put strain on the singer's voice. It also meant that otherwise impressive performances were cut because of small pitch problems. Auto Tune enables producers to correct the pitch of flat or sharp notes, saving time, money and reducing the workload for the artist.