[sdiy] simple 8k lowpass for ADC?

[Dan Snazelle]

i am putting audio ( a full track with vocals)  through an 8bit converter. it sounds fine until the vocals get close to sibilance...this
seems to overload the converter and make the sibilance far far worse to the point of almost white noise.

now when i simply put an eq on the track in Logic FIRST i dont have this issue.

so i would love to build a simple filter into the circuit but dont know what kind to use.

in Logic I am using a roll off which kills everything above 8-10 k (not a very steep curve)


with this on there is no issue with the ADC0820 based circuit....and i am NOT overloading the ADC
as far as levels or voltage go. so this must be an aliasing issue as the problem only arises when 
i sweep the sample rate toward lower clock rates.


SO....i tried using simple RC filters but they are not really working out too well.


anyone have any advice on the kind of filters they use on an ADC?

or maybe a homebrew switched cap filter i could clock off the clock?

thanks

(keep in mind this is meant to sound dirty anyway...just not crappy)