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, but what else are they used for - and what
about sounds where the time constants are less than optimum ? Historically, “LA” style limiters were
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 are 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 kill a few woofers.
7
