Hey there....so I'm in Logic Pro 8.0.2 and my external sidechain option doesn't work for the mcomp. I have the proper logic sidechain input selected (in this case a bus).... I enable the "s.c. ext" button... and I still get the internal sidechain signal (the material being compressed). This problem also occurs with my mix-pressor plug. I have the plugs' latest versions as of 2 months ago... whats going on?

I've been using the internal SC a bit lately and would like to explore the external SC option. How are you supposed to feed it?

I'm using Samp Pro v9...
Thanks.

When using the side-chain with the HPF set to say 60Hz, does the compressor actually not process any freqs below that or does it simply ignore those freqs while determining how to act based on the threshold setting (but yet still compresses the entire freq range)?

Whenever a VST version of the plug-in is used you need to set up the multi channel track before inserting the PSP MasterComp, this is a usual procedure for VST 2.4 plug-ins.
Side chain filters attenuate or boost low or high frequencies depending on the setup. Side chain filters allow you to choose how the compressor should react depending on the frequency. Sometimes you need to have a heavy kick or bass pumping so you boost low frequencies in the s.c. In most cases you need the compressor to be lighter on low frequencies as in most cases the kick still has enough energy in the mid range for proper and musical compression so you cut lows.
Side chain is a control signal path, whatever you do on a side chain signal reflects in the processor's behavior but doesn't change the processed sound directly.

Regards,