well,
according to the autofilter thingy you have to keep in mind that you will create a notchy, disturbing sond exactly at that freq. range you put the autofilter at, IF you put the slope too notchy. so if you increase the q (slope) it will do exactly the same like an eq. btw, eq and filter is pretty much the same if one didnt recognize already. so to the filter goes the same like to the eq, the faster the slope falling down, the more ringing at that range you need to expect. so what i do is trying to keep that ringing as low as possible by decreasing the q button and putting the slope down. the same i do while eqing usually, cause if you need to hardly correct with a fast slope it doesnt make any sense, cause you will get even more ringing after.
so try to keep slope falling down slow to avoid disturbing stuff. if you like the result, just try to seperate with an eq behind the autofilter, putting down some the range you set at the autofilter. that way you keep the sound, just putting down the disturbing area. often things are just disturbing because they suddenly appear louder than before and need to be corrected.
a fast falling slope is simply cutting at a specific point like this "l"....so from one moment to the other there´s nearly no sound of the freq. range you set. it´s cut at -30db maybe.... our ear is recognizing sounds hard cutted or raised much more easy than a range which is slightly set up/down. next to that it recognizes raised areas much more easy than put downs. soooo. this is someway the only reason why one should try doin a slightly smooth mix/cut (which one should rather see as kind of a fade like this "/") if your desire is to apply this smooth feeling to it without any noises or stuff.
on the other side our ear gets very fast tired and bored by hard hitting sounds, disturbing ringing freq. ranges, phase correlations and sure too much compressed/limited music (lack of dynamics and difference in rms)
this is why you can listen to fastest/craziest music and getting tired after just few minutes of listening. it´s not only the music itself which will drive you crazy, also it´s the content of this music and how it reaches our ear and our brain.
soo, to come back to the point xD the autofilter is quite a nice tool, but should not be used to eq a sound or stuff. but as far i was able to read (^^) this was not your intention. so if the use is resulting in a ringing type of sound or otherwise disturbing some specific freq. range in your audio material, just try to put the q factor down. usually this should help. if you like the ringing notchy sound (which i had quite often) you can simply leave it like this and try to slightly put down that freq. range with a good linear phase eq like psp neon or stuff.
another thing to clean up your mix is the use of good M/S tools and panning tools. i forgot that to mention while i was talking about arranging sounds in the space of a track last time. sooo, in short one can say each sound with a different reverb to set the depth, M/S to adjust the mono and side sections (kinda depth story too) and sure panning to adjust loc. from left to right. i just wanted to leave that, because i found the ableton live panning to be very unaccurate. also many sounds are not really mono, even if you set it up like that. different types of processing will result in spreading the mono content. so if you want something to be exacty mono or even something between mono/stereo, one should feel free to consider taking use of these very helpful tools. they´re not just for mastering stage and all these tools will make life someway much more easy if used wise.
my recommendation if one´s looking for a really sick tool and some familiar and not afraid to take use of these, i´d leave just one suggestion solving lot of issues during mixing stage even if you got no access to the source/project file:
http://www.brainworx-music.de/en/plugins
these are really state of the art plugins, but as like with most good ones, they´re not that cheap. so feel free to try before buy
some stuff i also like and im really sad i actually cant use the dyno plugin:
http://www.stillwellaudio.com/?page_id=28
these are somehow quite cool, i like their character, but this is exactly it. they got pretty much their own sound. decide on your own if you like them or not. i downed their original evaluation editions from their site i guess about half a year ago, but they seem really not to evaluate. anyways theres a message popping up eacht time you open the plugin, which shows up a message for a few seconds that it would be so kind if you do the right thing and register them. anyways, after this message is gone they work just fine

i got all of them and love to use badbassmojo i.e. on my bass section, because this ones really easy fattening it and "spreading" with a very smooth to absolutely aggressive character. at least i like it
one thing i want to leave is that these plugins are really working accurate and it depends often on your monitoring and your careful listening if you will recognize their work or not. so work a lot around with them, try to carefully listen, get familiar with their different characters and have some fun.
hope one doesnt mind the novel. just wanted to leave some more deep thought about how i get where i want to go. like i said to me it´s all about the mixing stage, and this sure is first about arranging the sonic content in the space you got. but this is a lot of work, one needs to be familiar with a few technical and physical aspects of music, signal flow and the function of the machines and softs you´re working with. at very first you need to know your monitors or spend a lot of money for really good and accurate monitoring and acoustics. im talking about accurate monitoring, no solutions like a 800 bucks genelec monitor. good monitoring starts anywhere at few thousand bucks each, imao the very start one could consider to take use of is a K&H O300 maybe. never had a listen to the bigger genelecs, maybe they´re good, but i dont like the clean sound of the smaller ones. i would love to have a listen to Event´s Opal, the new Equator Q10 and mostly i would love to have a listen to Tannoys Precision serious, especially the 8d. so cant tell about them, but K&H sounds just great, best i heared so far..... and before putting that much money into a 2 way system i would rather save few more bucks for three way.
anyways most experienced engineers still will recommend you a passive system, which most of us will not be able to pay. and secondly they will recommend to get more than just one system xD
anyways im a fan of digital stuff, im a child of the future. but still digital monitoring is quite expensive if you want to get it really accurate and true in response (the K&H start at 2.000€ each, which is quite cheap in their class of 3way monitoring). and at the end you can buy the most expensive monitoring system, if your room is not fit for them and your acoustix sucks in there, then you wont benefit any shit of it.... not talking bout the price of serious optimated acoustic installations......
so, imo this is nothing one should worry about. there are lot of artists doin great mixing on ipod mobile systems. so it´s just up to know about your system and know what you´re doing. i´d recommend all of guys like me out there, not able to pay these huge amounts of money, to keep your monitoring you bought first and work with it as long as you can. i would never sell mine, weither how cheap they are. and what i really found to be very interesting is soft like the IK ARC system. got it, impressed! just some fiddling and needs accurate measuring of the room. anyways, worth to consider... share the cost by 5 ppl and it´s worth every single penny
again pls excuse the novel, sorry for that, coffee´s guilty ^^ hehe
have fun, cheers
stephan