Okay I found a web site
http://www.calculatoredge.com/electr...low%20pass.htm that will calculate it for you.
I tried it, selected 8kHz and 1500 Ohms and three components, and got two 0.44 microfarad capacitors and a 21.2 Henry inductor. Oh and I selected 3 dB ripple, sort of arbitrarily.