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Lowpass filter for LTC6363

I'm trying to add a 1 pole RC filter with a 20kHz cutoff upstream of the LTC6363 as an anti-alias filter. My configuration is like this:

This is for audio frequency input signals and I'll be doing a 16x or 32x decimation factor to provide additional anti-alias performance.

According to LTSPICE I can add a 30nF capacitor as shown:

...and this gives me the magnitude response I'm after, but it adds a ton of noise @ 380kHz which I assume will alias into my input signal. If there's a more optimal solution please advise!