AEA rpq500 Owner's Manual page 13

In Line Input mode, the CurveShaper™ becomes a versatile EQ to add
presence or air to any line level signal on a mix or even in mastering.
Be careful when you add Curve Gain because this also affects the
overall gain structure of the preamplifier and could introduce overload
distortion. After you make this adjustment, you may need to reduce the
Mic Gain control (ref. #10) to compensate for the CurveShaper's™
signal boost.
Note: When the Curve Gain is fully counter-clockwise (set in the "0"
position), no EQ will be introduced into the signal. It essentially the
same as having the HF In switch (ref #8) disengaged.
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