Originally Posted by superbassman2000
My question for that author is how is it different from a single band semi-parametic EQ? it looks like it does the same thing
It's a low pass filter, like on an Alembic or Wal or ACG preamp. Parametric filters are band pass.
What the low pass filter does is remove frequencies above it's cutoff, just like a passive tone control, but you can sweep it.
I posted this in another thread. Here's a Low pass being swept followed by a high pass. A high pass passes the highs and removes the lows. LP/HP filter
Also.. Varitones are NOT high cut tone controls, they remove midrange. It seems to be common to call any rotary switch a Varitone, but it's not. For instance the ToneStyler is not a Varitone, it's a decade control. it switches in different value caps.
The low pass filter does the same sort of thing, but it continuously variable and most have a Q or resonance control that gives a peak at the cutoff frequency, so you can use that for a boost at the cutoff frequency.