Wall of Sound

The Wall of Sound (also called the Spector Sound) is a music production formula developed by American record producer Phil Spector at Gold Star Studios in the 1960s, with assistance from engineers Stan Ross, Larry Levine, and the session musician conglomerate known as "the Wrecking Crew". The intention was to create a dense aesthetic that came across well on AM radio and jukeboxes popular in the era. As Spector explained in 1964, "I was looking for a sound, a sound so strong that if the material was not the greatest, the sound would carry the record. It was a case of augmenting, augmenting. It all fitted together like a jigsaw."

In order to attain the Wall of Sound, Spector's arrangements called for large ensembles (including some instruments not generally used for ensemble playing, such as electric and acoustic guitars), with multiple instruments doubling and even tripling many of the parts to create a fuller, richer sound. Spector also included an array of orchestral instruments—strings, woodwind, brass and percussion—not previously associated with youth-oriented pop music, characterizing his methods as "a Wagnerian approach to rock & roll: little symphonies for the kids". Larry Levine recalled, "I found out later that there were other engineers along the way who tried to duplicate the Wall of Sound by turning up all the faders to get full saturation, but all that achieved was distortion."

The intricacies of the technique were unprecedented in the world of sound production for popular records. Wrecking Crew guitarist Barney Kessel would note: "Musically, it was terribly simple, but the way he recorded and miked it, they’d diffuse it so that you couldn't pick out any one instrument. Techniques like distortion and echo were not new, but Phil came along and took these to make sounds that had not been used in the past. I thought it was ingenious." According to Beach Boys leader Brian Wilson, who used the formula extensively: "In the '40s and '50s, arrangements were considered 'OK here, listen to that French horn' or 'listen to this string section now.' It was all a definite sound. There weren't combinations of sound, and with the advent of Phil Spector, we find sound combinations, which—scientifically speaking—is a brilliant aspect of sound production."

...
Wikipedia