Wayne did a pretty good job on clarifying some of the graphic versus parametric EQ differences, I think the primary
point based on some of the comments is that a parametric EQ can have a broader filter or a narrower filter than a graphic EQ, the ability to adjust the bandwidth, depth and center frequency is the advantage of a parametric. For example, you could set a narrow notch right on a
feedback frequency with one band and then use the next band to
address a very
broad but shallow dip in the response.
An
equalizer cannot correct room related problems such as room modes and cannot correct any time related issues such as
combfiltering, all it can do is adjust the amplitude response of the
system itself. Many time and
phase related issues do affect the resulting
frequency response, however these issues cannot be
identified as being time related with an
RTA nor can they be fixed via EQ, although you can spend a lot of time trying.
As far as a graphic EQ helping with
feedback and 'mud', it might, but as Wolf alluded to, there are a lot of other potential factors (mic and
speaker locations,
speaker patterns and aiming, mic selection and proper use, the room and acoustical environment,
etc.) that really should be addressed before blindly applying a graphic EQ.
The comment that you have
feedback as a result of the way the
stage is built is interesting as it sort of begs the question as to whether the problem is truly the way the
stage was built or more how the speakers and mics are implemted on that
stage.