fv1 input lowpass filter

[smear]

i understand we need the output 1k+2.2nf lowpass filter due to the sigma-delta converters. but how important are the input 1k+1nf lowpass filters?

i did see this thread, where frank mentions “rolling off the out-of-band high end a little prior to the ADC can only help”, which makes me think it's not too important.
http://www.spinsemi.com/forum/viewtopic.php?f=2&t=88

i’ve got an inverting opamp buffer before the fv1. so if it’s just to prevent the circuit from amplifying any up high frequency noise on the input, i’m thinking of using a filter in the feedback path of that buffer instead.

and while we're on the topic, i always thought the datasheet values of 1k and 1n resulted in a fairly high frequency lowpass. is there a reason that a slightly larger cap value wasn't recommended? 4.7nf seems like it'd keep the input signal even cleaner (~34kHz cutoff), while still being above the bandwidth of the fv1 when using the 32768Hz crystal.

any advice would be very much appreciated

[smear]

i'm dumb and didn't see this bit in the manual "The purpose of this input bypassing is to remove any high frequency noise from the input signals, and to provide a low impedance at very high frequencies."

so i'll take that as assurance enough and just use whichever similar cap values i have lying around