This is a Fairchild 673 ‘’Dynalizer’’ Dynamic Equalizer. According to John Klett, it uses the same slow optical system as the Fairchild 661 and 663 and operates as an automatic loudness control, applying a Fletcher-Munson Loudness curve which boosts the highs and lows as the level drops. The 673 was a staple in Joe Meek’s studio in the early ‘60s along with the Fairchild 660 and 661 limiters.
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