It is an expression that has no definite meaning. The most common one you can find is a . . . Analogy to the sound wall?; which in this case would not be a sound block formed by many instruments behind the Phil Spector style but rather a fast and uniform base layer of a Coltrane-style soloist. However, and because these pseudopublicitarian definitions serve both a sweep and a scrubbing, I have found it by rating the effect produced by an experimental white noise-generating machine that would help fall asleep.
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