In short, if the volume for either the low (bass thru mid) or the high (mid thru hi-hats) frequencies gets above a
certain level, the dualband pre-limiter will slowly turn the volume for those frequencies down.
If it stays below that level, the volume is slowly turned up. This way, the output volume is made
more constant, except for sudden peaks and drops.
The dualband pre-limiter is actually a simplified version of the multiband compressor/limiter,
using only two frequency bands, without clipping, which is only limits (it does not compress).
Please see the help text for the multiband compressor/limiter
for more information.
Goal
The goal of the dualband pre-limiter is to feed the multiband compressor/limiter with a more or less
constant signal.
Because the multiband compressor/limiter is usually set to respond very quickly to volume changes,
input with a very loud volume which is reduced strongly causes a very flat, over-compressed sound.
This can be reduced by reducing the speed with which the multiband compressor responds, but that also
reduces the effectiveness of the multiband compressor.
The dualband limiter, when set to respond very slowly, does not cause the flat and over-compressed
sound that would be caused by fast responding compressors. Sudden peaks are not removed very well,
unless they take a longer time. That's not a problem, because the multiband compressor/limiter will remove them
later on. Short loud burst don't cause an over-processed signal in the multiband compressor/limiter,
only continuously loud signals do.
See the images on the left.
In image 1, the original signal is displayed.
Image 2 shows the signal after being fed through the dualband limiter. The loud peak has been reduced,
only a bit at the start and more at the end. The lower volume sound slowly comes back after the peak.
Image 3 shows the signal after multiband limiting. The drop after the loud peak is almost completely
restored because the multiband limiter responds much faster to signal level changes than the dualband
limiter. The remaining peak at the start of the loud peak is also reduced strongly for the same reason.
When to use it
This implies that the dualband pre-limiter should be used when the input volume is very high. Note that
if the input volume is already at a rather constant level, another option would be to just reduce the
input level. This will have the same effect.
How to control the volume that is fed into the next processing step
The topmost sliders control the maximum output volume for low (bass) and high (treble) frequencies.
Lower them to reduce the volume that is fed into the next processing step.
