The slope or ratio is also difficult to simulate. The initial ratio is low and becomes higher
with more gain reduction until the leds light up fully and further reduction is not easy. This upper
limit of reduction is in the area of 20 dB or at the bottom of the GR meter where the ratio becomes
low again but this would be a severe setting that few engineers could use. Distortion becomes
audible at very deep limiting. In a tech shop, it is easy to drive the limiter to 20 dB of reduction and
beyond where the GR meter shows a flaw in that it "folds back". We put a higher priority on having
the meter show what the Opto was doing accurately with "normal settings" than extreme test bench
observations. Test benches don't make hit records.
So the Opto Limiters seem to be great for vocals, what else are they used for and what about
sounds where the time constants are less than optimum ? Historically "LA" style limiters are often
used for bass and guitar tracks. They can be ideal for brass, saxes, synths and similar sounds with
superb results. There are other compressors that work well for these instruments but few that are as
transparent. Usually, when you hear of an engineer using a non-Opto compressor for these
instruments it is usually framed with "for the crunch" or because they add some desired color. There
is only a very small number of "clean" general purpose variable time compressors which seem to
give Opto units competition - our Variable MU is at the top of that list. Where the "LA" style
limiters are not always appropriate is for percussion and for mixes where the percussion is just right.
The Opto typically reacts fast to peaks - fast enough to remove drums from a mix but not quite fast
enough to be called "brick wall". Individual drums tend to have a little of the initial transient let
through but the desirable tone of the drum is diminished. If used gently, this can be applied to
brighten up the attack of the drum, but it is difficult to apply in practice because drums can be very
dynamic. One great use is on the room mics. The initial drum sound is pulled down, then the natural
reverb is increased. Shades of early Led Zep. While we mentioned that "LA" style limiters are not
what we suggest for mixes, there are times when the drums are too loud or when the engineer can
mix "into" the limiter. Both techniques are possible but not necessarily easy. One trick is very little
movement on the GR meter. Some of our clients use the Opto on mixes as an effect. This application
is valid as long as the effect given and the effect desired are the same. There is not many options for
adjustment and fine tuning. The good news is that at least the Manley is clean enough to pass a good
mix. In a live sound setting the Opto will perform as a fine speaker protection device. Once again the
Threshold is set for minimal limiting with music and is just adjusted to encourage the pyrotechnician
to try harder tomorow to damage your system.
The Balance Control deserves some description. Often, with stereo tracks, once you apply
limiting the apparent left/right balance shifts a little - even in link. While the Link switch makes both
channels equal in gain reduction, the change may still happen. The clues we use to establish position
include volume, transients and ambience as well as delay and tone differences. Limiting involves
changes with the first three. We included a simple adjustment to assist slight trimming to restore the
desired image center. Turning the Balance control Left increases the Left input up 1 dB and
decreases the Right input by 4 dB and turning the Balance to the Right raises the right and lowers the
left. Use both Thresholds while using Link mode to create the desired reduction. It may be easiest to
"get in the ballpark" in normal mode. A slight change in Threshold and Output is expected when you
switch to Link.
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