Here we have one of the new suave optical Smoothies and the previous OTA model Smoothie.
I've spent a lot of time comparing the two listening closely for apparent differences. I've used Beyerdynamic DT770 cans that are pretty flat and neutral. I've played through multiple cabinets. Here's what I can pretty safely say:
1. There is no way anybody listening to you playing live would ever tell a difference between the two (assuming using the same settings) 2. Headroom on the older OTA version was not an issue for me, even with a hot G&L L2500 bass 3. With all settings (knobs) the same (at least as close as visually possible) the LED on the OTA does not trigger as fast as the optical and when it does, it releases much faster than the optical. Based on the metering, this is probably indicative of attack and release differences with the OTA having inherently faster release (and probably attack). However, in real life playing, I really didn't notice a difference. 4. With the sustain knob all the way clockwise, the OTA is unusable really. It is squashy and thuddy. The same setting with the optical still seems potentially useable, though still very squashed feeling. This is pretty picky though. I doubt most people would never desire to turn the sustain knob all the way up as the Smoothie doesn't seem to be intended for being used as a limiter.
This next statement is totally subjective:
Maybe, just maybe, the OTA is a little more raw sounding.
Or another way to say it is, maybe, just maybe the optical is a tad smoother. Very, very minor difference. Totally subjective here because I am using only my ear and would only possibly be noticeable with neutral headphones. Nobody would ever notice unless doing this same side-by-side isolated test. Again, I am only using my ear here and really digging to try and uncover any real tonal differences. But, I used four different basses with both compressors ranging from a P/J setup, to G&L MFD's, to fretless, to Bartolini pre/humbuckers.
Bottom line: I'd personally be completely satisfied with either. Both sound fantastic. Both are very versatile. Both have the same build quality and identical in function. @bongomania has done a fantastic job rolling out a new optical version that is so close to the OTA it's crazy. I guess given the choice, I'd opt for the newer optical due to the charge pump to boost the 9V supply to a higher internal voltage. Really, both are impressive compressors. The Smoothie is easy to dial in and just plain works so well.
Retail price: $225