Specifications

13
Operating Manual - CLX-52 and CLX-51 Compressor/Limiter
our earlier limiter prototypes which measured fine and
sounded terrible. This led us to use a purely subjective
approach in the design of the detector - we did a lot of
listening to determine what sounded good and what didn’t.
Two important features emerged from this re-
search:
1. We designed the detector to let the attack and
release times speed up as more and more limiting occurs.
The compression ratio also increases. This lets us main-
tain peaks fairly close to a constant ceiling level, but al-
lows the illusion of increasing loudness as input level
increases, thereby preventing complete loss of dynamics
when limiting.
2. We incorporate a Double Release Time Con-
stant. When release time was set slow with a single time
constant, transients such as mic “pops” caused a quick
reduction in gain and a slow fade-up, making the action
of the limiter very obvious. With the double time con-
stant, release from gain reduction after a brief transient
is always fast, with a slower release after a sustained over-
drive.
When choosing a compressor/limiter, you can see
that it is very important to listen to it in your particular
application and see that it sounds the way you want. There
are lots of these devices with seemingly excellent specs
which sound very different with real program material
applied to them.
Peak Or RMS
There are several ways of looking at a signal to
determine its level. A peak detector looks at the maxi-
mum voltage a signal reaches regardless of it’s waveform,
while an RMS (root mean square) detector looks at the
energy in a signal regardless of the short term voltage
levels. This makes a peak detector the correct choice for
preventing clipping, overmodulation, or tape saturation,
while an RMS detector can be used to restrict material to
a given loudness. When an RMS limiter is used to pre-
vent clipping, the result is unpredictable. For instance, a
flute and a snare drum which are limited to the same RMS
level might have peak levels as much as 30dB apart! Use
peak limiters to prevent clipping.
10. TROUBLESHOOTING TIPS
Note: Unshielded cables, improperly wired con-
nectors, and cables with broken strands of wire are very
common problems. Use quality cables with quality, cor-
rectly wired connectors.
No Output
Check AC Power. Is the power switch on? Check
input and output connections - are they reversed? Are
you sure you have an input signal?
Controls Have No Effect
Is the Limiter In/Out switch In? Perhaps the Ra-
tio control is set too low to produce an audible effect or
the input level is below threshold. Is the Threshold LED
lighting up? If not, lower the threshold setting or increase
the gain. Do not expect to hear any effect when the input
level is below threshold, since the unit is simply a linear
amplifier at those levels.
When Using Heavy Compression, Background Noise
Is Noticeable During Quiet Sections Of The Program
As defined in the section on compression, quiet
program material is effectively made louder while loud
peaks are made quieter. When the program source is thus
raised in volume, its noise floor is also raised in volume
by a proportionate amount. This is not a defect in the
Compressor/Limiter, but an unavoidable side effect of the
gain altering process. If the noise becomes a problem,
the solutions are to either decrease noise at the program
source, or use less compression.
Excessive Hum Or Noise
Hum is often caused by a “ground loop” between
components. Try using the suggested balanced input and
output hookups if the other pieces of equipment used in
conjunction with the CLX unit have balanced inputs and
outputs. Noise can also be caused by insufficient drive
levels. Make sure you are sending a nominal 0 dBV line
level signal to the unit.