Thanks, Don. Your filter shows much more response variation with a capacitive load than the 230 kHz filter in the Murata curves. I don't think anyone adds capacitance on purpose. In the past I have used pots instead of fixed 330 ohm resistors and adjusted them for minimum detected audio distortion. Since I now have quite a few spare filters, these days I just swap in another one, trying both orientations for minimum distortion.
Before I wrote this program, I used to worry a lot more about audio distortion:
Brian
