Hiding A Lisp

I am a new to Garageband so maybe there are some good effects to filter out the frequency of the lisp? Most vocalists use a pop filter between the microphone and the singer to suppress pops and sibilance. You can use a pair of tights/ light material stockings around a metal coat hanger or buy a pop filter for about $15.

If you mean lisp like 'S's' and 'T's', try using the AULowpass. It takes out the high frequencies.

Just play around with it a little bit, you can adjust which frequencies you're canceling out.

In the Track Info Pane, make sure the Details arrow is down, choose one of the effects drop-down menus (they should read None if you just have a Basic track) and choose the AU from there.

a low pass filter is a pretty standard effect, any search results on the web you find would apply to the effect that GB has.

that said, personally i wouldn't use a low pass filter, but rather one of the many EQs GB offer. parametric would be my first choice, but if you don't know how to use one (again, web search could teach you) any of the Graphic EQs could be useful, and are quite easy to operate.

and of course the absolutely best solution is to try to practice speaking to avoid sibilants, if at all possible.

it takes a bit more then a forum post to really explain a parametric EQ, which is why i'd suggest doing some web searches on it.

the mini course is: tighten the Q, boost the gain and sweep through the frequency range to find the offending sound, tweak the Q, and then reduce the gain to try to hide the sound more.

best of luck with your speech work, fixing the issue is WAY better than fiddling with effects to hide it, hopefully you can get to a good level of satisfaction soon.