With the introduction of multi-track recording, it became possible to record instruments and singers separately and at different times on different tracks on tape, although it was not until the 1970s that the large recording companies began to adopt this practice widely, and throughout the 1960s many "pop" classics were still recorded live in a single take. After the 1960s, the emphasis shifted to isolation and sound-proofing, with treatments like echo and reverberation added separately during the mixing process, rather than being blended in during the recording. One regrettable outcome of this trend, which coincided with rising inner-city property values, was that many of the largest studios were either demolished or redeveloped for other uses. In the mid 20th century, recordings were analog, made on ¼-inch or ½-inch magnetic tape, or, more rarely, on 35mm magnetic film, with multitrack recording reaching 8 tracks in the 1950s, 16 in 1968, and 32 in the 1970s. The commonest such tape is the 2-inch analog, capable of containing up to 24 individual tracks. Generally, after an audio mix is set up on a 24-track tape machine, the signal is played back and sent to a different machine, which records the combined signals (called printing) to a ½-inch 2-track stereo tape, called a master.
Before digital recording, the total number of available tracks onto which one could record was measured in multiples of 24, based on the number of 24-track tape machines being used. In the 2010s, most recording studios now use digital recording equipment, which limits the number of available tracks only on the basis of the mixing console's or computer hardware interface's capacity and the ability of the hardware to cope with processing demands. Analog tape machines are still used by some audiophiles and sound engineers, who believe that digitally recorded audio as sounding too harsh and who believe that tape has a "warmer" sound. The scarcity and age of analog tape machines has increased their value, as does the fact that some audio engineers still believe in recording to analog tape.