How did Les Paul and the Beatles layer sound on tape, and where did stereo come in?

Multitrack recording lets each sound go onto its own track on the same tape, so that the parts can be recorded at different times and combined afterwards. Developed in 1955, it records multiple sound sources, or sources recorded at different times, to separate tracks to create a cohesive whole. Before it, all the singers and players had to perform at the same time in the same space. With separate tracks, the engineer could adjust the level and tone of each one, and redo a track or overdub a part to get a better take.

The pioneer was the guitarist Les Paul. On "Lover (When You're Near Me)" he played eight guitar parts, some recorded at half speed so that they play back double-fast. He built it up disc by disc, and by the time he was happy he had thrown away some five hundred recording discs. In 1949 Bing Crosby gave him one of the first Ampex Model 200A tape recorders, and he added an extra playback head so that he could play along with a recorded track and mix both onto a new one. Later an 8-track Ampex machine was sold to him for $10,000, and it became known as the Octopus.

The Beatles pushed the idea on a smaller machine. Sgt. Pepper was recorded on four-track equipment, because eight-track recorders were not operational in London studios until late 1967. They used reduction mixing: one to four tracks were mixed down onto a master four-track machine, giving the group a virtual multitrack studio.

When the recording is done, the many tracks are mixed down to a two-track stereo recording for duplication and distribution. Stereo uses two independent channels, played through two loudspeakers or headphones, to create the impression of sound from different directions, and a control called a pan-pot places each track by changing how loud it is in each speaker.