Before the advent of digital recording was the era of analog electronics technology. All music was recorded on reel-to-reel tapes, which were then used in the step-by-step post-processing.
Early audio tape only had 4 tracks. Later, 8-track tape was invented, and then 16-track, 24-track, and even ultrawide reels with 48 tracks. When only 4-track tape was available, two tracks had to be reserved for the right and left sound channels for the vocalists, so all the accompanying instruments had to be recorded on the other two tracks.
Generally, the rhythm section, including the drums, bass, and guitar, would be recorded first, simultaneously. Next, the stringed and wind instrument sections were recorded. Then the recording engineer would mix the four tracks of the rhythm section and the other instruments onto two tracks to leave two tracks for the vocalist. Later, the number of tracks increased, and ultrawide multi-track audio tape was invented. The recording equipment, which gradually disappeared after the dawn of the digital era, has become increasingly valuable.
