[sdiy] simple 8k lowpass for ADC?

[Tom Wiltshire]

For filter design, I like the Analog Devices tool at:

http://www.analog.com/Analog_Root/static/techSupport/designTools/ 
interactiveTools/filter/filter.html

They've made it a bit more awkward recently, but the java applet  
itself is still very useful. Don't worry much about what you type on  
the first page, and don't worry about the choice of op-amps it gives  
you - the important bit is the "Design filter" link (any of 'em)  
which appears in the table of suggested op-amps.

There's also the Elliot Sound pages on Op-amps, which has a lot of  
audio filter stuff:

http://sound.westhost.com/articles/dwopa.htm

For what it's worth, before I found the AD tool, I used to find a  
design that uses something similar (say, an analog delay with an anti- 
alising filter on the input), find out the cutoff of that, copy the  
filter part, and then multiply the values accordingly. Not a great  
methodology, but mostly successful.

HTH,
Tom

On 20 Jul 2009, at 19:15, Dan Snazelle wrote:

>
> 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)
>
>
>
>
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