Yeah that makes sense now - reactance decreases with increased frequency (1.59MΩ @ 1kHz, 159KΩ @ 10kHz and 15k9Ω @ 100kHz). So, with a larger impedance at the input, higher frequencies take the path to ground, right? If that's correct, does that mean that I should make C2 a smaller value as with a 1M2Ω impedance, I might be losing some higher frequencies of interest, e.g. c.1.3kHz - 15kHz? Or have a got that wrong..!
Thanks.
Thanks.