Not totally. It diminishes certain frequency ranges as you adjust the knob. It is hard to understand if you cannot turn it on and off and sweep it to hear the results, but if you have a foot pedal for the Standby, it can also control the Notch filter too.
If the Notch is working at a certain freq and you are in it's range, then it could indeed cause the note to deteriorate oddly at low volumes, although I have had that problem on mine.
If you - or anyone - wants to know how to set that foot pedal up to make both the Notch Filter and the Standby to work, I'll post the way to do it. Otherwise the amp isn't being used to it's full capacity.
On the B-200 series, the Notch Filter is always on and you just have to find an freq zone where it doesn't impede your playing.
And NO. Acoustic doesn't know what pedals work, they don't sell one nor have the specs for the right one either. It took me a lot of research to get it to work and don't count on Acoustic to help.