revert unintended edit

doc/classes/AudioEffectFilter.xml

@@ -17,7 +17,7 @@
 			Steepnes of the cutoff curve in dB per octave, also known as order of the filter. Higher orders have a more aggressive cutoff.
 		</member>
 		<member name="gain" type="float" setter="set_gain" getter="get_gain" default="1.0">
-			Boosts frequencies at the cutoff.
+			Gain amount of the frequencies after the filter.
 		</member>
 		<member name="resonance" type="float" setter="set_resonance" getter="get_resonance" default="0.5">
 			Amount of boost in the frequency range near the cutoff frequency.