You don't need a scope for this (and please don't buy one thinking that it will make everything ok)
I explained the basic theory behind the kind of filters you should use. The external capacitors have nothing to do with the update rate and settling time and the rise time of the ADC or DAC. You do not need to take these into account for most applications.
Also, by including inductance, you have now introduced a resonant frequency within your circuit. This is another reason to avoid adding inductive components to a circuit. Now, if you happen to input that particular frequency in the RLC (or LC) circuit, the gain will be really large and the circuit will ring or oscillate at that frequency. Something like this should always be avoided unless you need a resonant circuit for a specific reason.. In this case, you do not.
Everything you have advise up to yet did not work for my situation, and I am afraid for what I am creating I do need a scope:) I do need to take into account the update rate and settling time and the rise time of the ADC and DAC.
This is what they did in the old days, old is gold:) whatever.......caps inductors resistors they are all filters ok:)
http://en.wikipedia.org/wiki/Electronic_filter
Passive filters
Passive implementations of linear filters are based on combinations of resistors (R), inductors (L) and capacitors (C). These types are collectively known as passive filters, because they do not depend upon an external power supply and/or they do not contain active components such as transistors.
Inductors block high-frequency signals and conduct low-frequency signals, while capacitors do the reverse. A filter in which the signal passes through an inductor, or in which a capacitor provides a path to ground, presents less attenuation to low-frequency signals than high-frequency signals and is a low-pass filter. If the signal passes through a capacitor, or has a path to ground through an inductor, then the filter presents less attenuation to high-frequency signals than low-frequency signals and is a high-pass filter. Resistors on their own have no frequency-selective properties, but are added to inductors and capacitors to determine the time-constants of the circuit, and therefore the frequencies to which it responds.
The inductors and capacitors are the reactive elements of the filter. The number of elements determines the order of the filter. In this context, an LC tuned circuit being used in a band-pass or band-stop filter is considered a single element even though it consists of two components.
At high frequencies (above about 100 megahertz), sometimes the inductors consist of single loops or strips of sheet metal, and the capacitors consist of adjacent strips of metal. These inductive or capacitive pieces of metal are called stubs.
hahah cool it looks like I was not far off but by my calculation 48khz is 2100 picofarads:P I am just guessing tho