Determine how steep is the filter's shelf transition.
@end table
+@section tremolo
+
+Sinusoidal amplitude modulation.
+
+The filter accepts the following options:
+
+@table @option
+@item f
+Modulation frequency in Hertz. Modulation frequencies in the subharmonic range
+(20 Hz or lower) will result in a tremolo effect.
+This filter may also be used as a ring modulator by specifying
+a modulation frequency higher than 20 Hz.
+Range is 0.1 - 20000.0. Default value is 5.0 Hz.
+
+@item d
+Depth of modulation as a percentage. Range is 0.0 - 1.0.
+Default value is 0.5.
+@end table
+
@section volume
Adjust the input audio volume.