SPL's BiG is a double-slot 500 series module designed by the same minds that brought you the SPL Iron Mastering Compressor. BiG uses stereo information-audio with little or no correlation between the left and right channels and allows manipulation using three simple hardware controls. No matter how much you use it, BiG processing collapses accurately down to mono.
The stereo L and R audio inputs of BiG are algebraically summed to produce a full-spectrum mono signal that no longer contains out-of-phase (non-correlated) information such as reverb and delays. This signal is processed through a specialized filter set that has three, interacting controls: Range, Stage, and Bigness. I tried BiG on full mixes as well as individual stereo instruments that had L/R channels of un-correlated sound.
With the Bigness knob set to mid-way and both the Range and Stage controls off, I did notice hot percussive levels were compressed and re-adjusting working levels downward ameliorated some of the loss of transients.
I tried the Range control that selects the frequency processing range. Range set to High dials in a "fizz factor" with cymbal crashes and other bright sounds taking on a new clarity. Range set to Open seems to bring up the lower mid-range band and is noticeable on electric guitars and vocals.
The Stage control moves the frequencies set up in Range backward or forward in the stereo field with the effect of the sound either wrapping around you or it is positioned more in front of your listening position. Lastly, there is a switchable 1.5dB @ 80Hz bass boost using a passive filter circuit similar to the Iron's AirBass function. For me, this can stay on all the time.
The SPL BiG 500 Series module is distributed by Focal-Naim America in the U.S. and Canada, and sells for $649 MSRP.