In general for guitar effects graphic is the way to go. Parametrics are hands down better, but you cant get really good quality and control/flexibility out of conventional 'guitar effects' budgets. To put this in perspective, the reference standard parametric, designed by the guy that invented parametrics, is the GML8200, which is just 5 bands stereo, and costs about £4,500.
When using graphics just remember that the bands almost always overlap, use it for refinement of a sound that is as close as you can get it on the settings on the amp (i.e. less is more) and you should be fine.
I wonder if I could slightly hijack this thread a little as I have a related question on EQ's. I'll start another thread if you prefer.
I've never used an EQ before and I know nothing about the engineering of sound so you can take it as read that my knowledge is non-existent, however, when I bought my Digitech RP1000 I noticed it had a parametric EQ but I'm finding it a bit confusing. I understand that I can boost the highs, mids and lows but I'm also able to specify a particular frequency for each of these and that's where I'm lost. For a 24 fret guitar with a trem that plays both rhythm and lead, what should I set the frequencies to for bass, mid and high? I'm thinking that I'll start by adjust the EQ on the amp so the EQ on the RP1000 can be used to fine tune the tone and provide a boost in some songs. I realise I can change the frequencies on this system for every song we do but frankly, I don't want it that complicated. I just want to set the frequencies so they're the same on every patch and then just change the amount of boost on each one to suit. So, can anyone tell me what frequencies to use for bass, mid and high?
Guitar sound consists largely of overtones. The fundamental of the lowest note on a guitar depending on tuning will be between about 55 and 82hz, and is likely to be eliminated altogether to let the bass handle that. A common first thing to do is to cut out everything below 100Hz. Above that, you need to keep some low mids and mids for the fundamentals of higher notes, but by and large youre dealing with broadband sound from overtones that can be shaped to your taste without much musical impact. There is sometimes a need to EQ differently for different tunings, but thats generally in a recording and mixing setting, and would be overkill for live or playing for your own amusement.
Very, very, VERY roughly (and more than a little debatably) speaking, its something like this:
<100hz. Kill. Probably. Up to you, but its generally quite wise.
100-150: 'bass' (which is really the first overtones of the lowest notes)
150-400: meat and chunk, and quite a lot of note fundamentals.
400-1k: kinda honky, forward, cardboardy mids. Lots of this drives your sound forward but robs it of depth and thickness. Careful, still qutie a lot of note fundamentals in here.
1k-2k very forward, punchy, inyourface mids. Can also detract from apparent thickness and depth if overly present.
2k-4k: Main range for pick attack and definition. Very loud to the human hear. Many ultrascooped sounds have everything but this and 100-200hz or so ripped out of them.
4k-6k: bit and fizz.
6k+ here be dragons. 'Air' and some more fizz. Questionable how much of it is really there. Many people just rip it out completely, some dial more in for a more open sound. May invite more fizz due to overlapping with fizz range in the EQs band Qs (Q means width, basically, which is fixed for graphics and variable for parametrics). If in doubt just leave it alone.
