I love a useful freebie - who doesn't? So I've been testing BoostX.
I tried it on a drum bus that previously had an instance of Pro-L on it. The initial results sounded pretty all right, though obviously not as transparent as Pro-L. (Yes, I know it's unfair to compare a freebie to a fairly expensive product, but you have to establish some kind of standard of what's possible.)
Be aware that the description of BoostX is a little misleading . It says that quiet parts are boosted while peaks are left alone, which isn't quite accurate. Setting the slider to 3db resulted in an increase in peak value of 2db, and setting the slider to 6db resulted in a peak increase of 4.5db. IOW, it's a volume control with some peak limiting.
That doesn't mean it's not useful. The idea of upward compression is to raise the average RMS, which BoostX does do. However, if it also raises peak values then much of its effect could be achieved with nothing but a volume control. Here's how I tested:
I exported a measure of the soloed drum track and used Adobe Audition to calculate the average RMS with the raw track, with Pro-L and with BoostX. Each was adjusted so that peak values were close to the same (BoostX was touchy to tweak, so when I got it to 0.3db higher than the raw peak I said "close enough".)
The unaffected track had an average RMS of -20.4db. BoostX only brought it up to -19.4db, because in order to keep the peaks legal I could only set the BoostX slider to 1db; any higher, and the peak values got out of hand. Pro-L brought the average RMS to -16db, such that the track sounded 4db louder without raising peak values. That's what upward compression is supposed to do.
Sadly, BoostX is just OK. If you're looking for something along these lines I'd recommend trying out the free
LoudMax plugin.