Gullfoss is an adaptive mastering equaliser.
Gullfoss sorts out clashes between frequencies.
Recover = brings up the level of the overwhelmed instruments.
Tame = brings down the level of the overwhelming instruments.
Sound theory recommends splitting the load between the recover, and tame controls — but you don’t have too.
Over 100% it can make things start to sound unnatural.
There’s a meter along the bottom of the spectrum indicating if the process is too bright, or too dark. If the meter is heading right, the process is too bright, and heading towards the left; it’s darkening the sound.
There’s another meter on the left of the spectrum showing the relative amounts of recovery and taming.
With each of these meters, aiming for the middle is a good starting point, but, of course, adjust for taste.
Bias = bias towards recovery or taming. A negative value bias towards recovery, a positive value towards taming.
Brighten = Either brighten or darken the track, a positive being towards brightened, a negative towards darkened.
Boost — Imposes the effects of the Fletcher Munson curve, similar to a loudness control. A negative value favours the mid-range, where our ears are most sensitive.
There are two processing limits, allowing you to select which boundaries of the frequency range. They overlap too, allowing you to exclude the mid-range, which could be interesting.