Some things seem a little off, here.
The typical pump effect is heard when you put multiple tracks through the same compressor, allowing the loudest signal in the group to trigger the compressor (typically kick or bass).
You wont hear much “pump” a) by mixing parallel compressed and uncompressed signals and b) by only putting the bass through the comp.
Parallel compression is typically used to raise the overall noise level of a track or submix. Usually you apply it to a whole mix, or something like a drum submix. You want to keep all the frequency content in the signal, not strip it down to the bass. In parallel compression, usually you aim to squeeze out all the dynamics (high ratio, low threshold, short attack, short release so it churns a lot) and then a strong amount of make-up gain to bring the signal back up. The compressed signal, in a parallel config should be very noisy. You then mix this into the dry signal, which should give it more energy.
I don’t know why you’re getting a lower overall volume. This happens to me a lot when I try parallel compression in my Rytm. I guess it’s a phase issue? Or your meters show RMS - the consistently lower dynamic range might pull the average level of the signal down, even if peaks are occasionally higher.
I usually just crank the make-up higher, or the overall (dry and wet) level higher, give up on parallel and try another approach.
Given 3, maybe my theory in 1 and 2 needs work.
If you really want your track to pump, don’t use parallel. Push your whole mix through the compressor, perhaps with higher bass levels than you’d guess (to ensure the compressor engages due to kick or bass), and set a rhythmic release time that shows up the groove you’re aiming for. You probably need lower ratio and higher threshold than your initial guess.
Also consider other techniques to make kicks or bass more punchy:
- don’t have anything play when the bass plays
- use shorter bass notes, so there’s more emptiness in the low end between the hits/notes (you’ll have to work to get the right balance here. The real weighty tones usually need a longer attack or sustain phase to show themselves - because the wavelength is longer)
- eq off the low end from the bass when the kick hits (or vice versa), so they don’t muddy one another
- shelve the low end off everything else to give the kick and/or bass more bandwidth to show themselves
- some times your bass needs more high end to tell the ear where it is
If you want deeper overall tone, reduce the high end on everything… just a little. 0.5-1 db is plenty. Then turn everything up a blittle.