Used to use one when I had a PA rack. Best way to describe it is what a musician friend said " its like you took a blanket off the speakers. " Try it inline before your powered speakers. Some keyboards now nave a similar effect built in. Let us know your results.
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Bill in SC --- Roland BK9 (2) Roland BK7M, Roland PK5 Pedals, Roland FP90, Roland CM30 (2), JBL Eon Ones (2) JBL 610 Monitor, Behringer Sub, EV mics, Apple iPad (2) Behringer DJ mixer