Ashly S CL-100 User Manual

ASHLY

owner’s manual

CL-100 CL-50E CL52E
LIMHER/COMPRESSORS

ASHLY AUDIO, INC^

TABLE OF COWranS

Introduction....................................................2

If You Are In A Hurry

.......................................

Mechanical Installation....................................3

Wiring.............................................................3

Stereo Tie, Detector Patch, Alternatives for Sound
System Installations

Controls And Indicators...................................5

Gain, Ratio, Attack Hme, Release Time, Output Level,

Bypass Switch, Threshold/Gain Reduction Indicators

Initial Setup And Checkout

Theory

Applications

Special Notes On the CL-52E.....................

.....................................................

The Need for Gain Control, Gain Riding, What Compressors

and Limiters Do, Compressor/Limiter Circuitry, The Aahly

VCA (Voltage Controlled Amplifier), Detectors

.............................................

The C!ompres8or/Liiniter as a Protective Device, Alternatives
for Sound System Installations, Compression for Feedback

Control, Recording, De-essing, The Compressor/Limiter as a
Special Effects Device, Using the CL-Series on Stage,
Voice-Over Compression (Ducking), Stereo Operation

Gain Reduction Meter Display, Output Level Meter Display,
Gain Reduction In/Out Switches, Stereo Tie Switch

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2

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19

In Case of Trouble..........................................28

Glossary........................................................30

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IMTBODUCTION

The Ashly CL-SERIES of Peak Compressor/Limiters was designed in
response to the need for a universal peak-sensitive automatic gain control
(AGC) device with audio performance comparable to that of a professional

mixing console. It took over five years of research to realize this goal, with
much of that time spent in developing a wide-bandwidth, ultra-low­distortion, low-noise VGA (voltage controlled amplifier). The resulting
product is a versatile and highly listenable compressor/Umiter suitable for
use in professional sound reinforcement, recording and broadcasting.

The Ashly CL-52E Stereo Peak Compressor/Limiter was developed to

meet the need for a stereo compressor/limiter that maintains correct stereo
imaging at all times. The CL-100 is the half-rack version of the CL-50E. The
greater part of the text and illustrations in this manual therefore refers to
the CL-50E. Special features of the CL-52E are explained separately. We ask
that you please read this instruction manual thoroughly before operation so
that you may realize all the features and benefits that the Ashly Compressor/

limiter has to offer. □

IF YOU ARE IN A HURRY

4. If you have problems, please refer to the more detailed sections and to
the troublediootu^ guide in this manual. Q

T

MECHANICAL IW«™i i AUftii

The CL-50E and Clr52E Compressor/limiters mount in a standard 19
inch equipment rack. The mounting screw threads vary with different rack
manufacturers and you should refer to your rack instructions for proper
hardware. An oval head or flat head screw with a plastic countersink washer
is preferred to protect the finish of the compressor/limiter under the screw.
The CL-100 is housed in an indusby standard half-rack enclosure which

provides a variety of mounting options. It can be used free-standing, in a half­rack-sized enclosure, mounted in a vertical 19 inch adaptor with up to eight
other half-rack products, or side by side with another half-rack product in a
standard 19-iiKh rack. Mounting accessories are available fixtm Ashly to
accomplish this.

Your Ashly compressor/limiter is housed in a rugged steel case and will

tolerate moderate abuse. However, for road systems which may be dropped
or otherwise subjected to extreme forces, we recommend some rear support
for the chassis to prevent bending the fient panel when these forces occur. □

We will assume that you are femiliar with compressor/limiters in

general. Please keep the following points in mind:

1. For safety, your CL-50E or CL-62E should be connected to a standard
ground AC outlet supplying 120 volts, SOHz. The CL-100 uses
standard rcTnote RAPS power pack. This should also be connected to
a grounded 120 vdt, 60Hz outlet.

2. The inputs and outputs of Ashly compressor/limiters can be used as

either balanced or unbalanced depending on the connector. For
unbalanced connections, use a standard mono phone plug. For
balanced (xnnections, use a stereo phone plug with the (+) signal on

the tip, the {-) signal on the ring, and the ground on the sleeve.

3. For a good starting point, set the input and output levels at V” and
the ratio, attack, and release controls at mid-rotation. Apply signal

and adjust from there to suit your application.

WIRING

The CL-50E and CL-52E Compressor/limiter should be connected to a

3-wiie grounded outlet supplying 120 Volts, 50-60 Hz. Power consumption is

12 watts. The CL-100 uses a standard RAP-6 remote AC power supply.

The INPUT is a 10k ohm active balanced type on a standard stereo
phone plug that will accept levels of up to +20 dBV. The (+) or in-phase
connection is on the tip and the (-) or out-of-phase connection is on the ring.

To use the input as a common unbalanced type, simply use a mono phone

plug in the usual way.

The OUTPUT connection is a standard 1/4” phone jack and mates with a

standard phone plug such as a Switchcraft 280. Output impedance is 200

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ohms, and fiill headroom is realized with any load of600 ohms or greater. For
rack-mounted unbalanced audio ^^ms the output ground may be
separated from the case ground by using a stereo phone plug for the output
connection. The output ground is then wired to the ring of the stereo plugs

rather than the sleeve. In this manner, ground loops in the rack may be
eliminated. Ihis output can be fed to a balanced input by wiring the (+) input
to the tip, the (-) input to the ring, and the shield to ground

Stereo Tie

This patch point is used to tie tc^ether two or more CL-SOE’s (or
CLrlOO’s) for stereo or multi-channel operation. To connect, place a patch
cord between the STEREO TIE connections of both units. If signal ground
isolation is being used, be sure to use a stereo patch cord

NOTE: If more than two units are to be tied together, use a common “Y”
type adaptor to split the signal as necessary. The Stereo He point actually
represents the DC output of the detector circuit When tied in parallel for
stereo operation, the VGA’s of the two units will both respond to the most

negative control voltage present at the Stereo Tie point, thus insuring that
the stereo image never shifts left or right. The Stereo He points of CL-50E’s
and CL-lOO’s may be directly interconnected.

Detector Patch

The CL-50E and CL-100 Compressor/Iimitere have a DETECTOR

PATCH point whidi can be used in conjunction with an equalizer to produce
frequency-sensitive limiting. This and other uses of the Detector Patch are
discussed later.

Alternatives For Compressor/Limiter Sound System installations

To install the CL unit in a sound system using a passive crossover,

insert it between your mixing console output and the power amplifier input.

For systems using electronic crossovers, there are two ways to use an Ashly
compressor/limiter. If it is inserted between the console output and the

crossover input, it will act on the entire audio frequency spectrum.
Alternately, the compressor/limiter may be inserted between an output of the

electronic crossover and the input of a power amp, in which case it will only
affect a specific band of firequencies. □

COMTROLS AND INDICATORS

Gain

The gain control is used to match the level of the signal source to the
fixed 0 dBV threshold of your Compressor/limiter. It should be adjusted so
the yellow threshold indicator iUuminates only when the signal reaches the
maximum level desired Then, above this level, the O)mpressor/Iimiter will
tend to minimize further increases in level.

Ratio

This control determines the ratio of change in output level to changes in
input level for all signals above threshold The numbers printed around the
Ratio control are calibrated in dB and indicate the dB increase in input above
threshold required to produce a 1 dB increase in output. This can be
expressed conveniently as a ratio. If the output remains constant no matter
how high the input level, we have an infinite (<») input/output ratio. It should
be remembered that the Ratio control has no effect on signals which are
below threshold, since the CLrSERIES products do not alter signals at below-

threshold levels.

There is a common but incorrect notion that limiting always implies the
use of an infinite ratio. Although there are times when an infinite ratio is
desirable, there will be situations where infinite, or “hard”, limiting action is
neither appropriate nor necessary. In fact, it should be noted that an infinite
ratio setting is likely to cause noticeable side effects in the sound, and may
not be usable on programs where subtle control is desired

Attack Time

The response of the compressor/limiter to signal levels above threshold
is fiuther defined by the ATTACK TIME control. Attack time is the amount
of time that the unit takes to attenuate the output level after threshold has

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been reached. For veiy fast transients, such as hand claps, snare drums, or
other percussive soimds, a very fast attack time is usually desirable so that
the limiter can respond in time to control the peak level. On other types of
program material, a slower attack time may be preferred. A too-fast attack
may, on some material, “square ofiT the top of a waveform, produtíng a
distorted sound. The Ashly CL Series provides continuously variable attack
times finom 200 microseconds to 20 milliseconds.

Release Time

Another parameter which affects oompressordimiter performance is
Release time, or the time required for the limiter to restore system gain to
nonnal after the input agnal has fallen below threshold level. Again, proper
Release tíme will depend on the type of program material being processed
and the way in which the limiter is being used.

When subtle limiting is desired, slow release times are often chosen to
avoid a condition referred to as “pumping” or “breathing”. This occurs when
overall gain is modulated up and down by repeated peaks which are followed
by quieter intervals. If the release time is set too fast, then the overall level
will jump up and down, producing an objectionable and unsettling effect.
Note that, in some cases, an individual track or channel which seems to be
pumping may sound acceptable when heard in context of a complete mix.

A unique feature of the Ashly Compressor/Liiniters is the incorporation
of a double release-time constant. When a conventional compressor/limiter is
adjusted for slow release times, transients such as mic “pops” and record
scratches may cause a severe reduction in gain followed by a slow fade-up,
making the action of the limiter very obvious. Wi\h the double time constant,

release from gain reduction after a brief transient is always fast, with a
slower release after a sustained overdrive.

Output Leve/

Because compression and limiting are both gain reduction processes,
the output of a oompression^limiter is frequently at a lower level than the
nominal system level. To make up for this loss, an OUTPUT level control is

provided to restore up to 18 dB of system gain, NOTE: When the unit is in
the BYPASS mode the OUTPUT control still functions.

Bypass Switch

This switch enables you to quickly switch the CL compressor/limiter in

or out of the audio chain, making comparisons between processed and

unprocessed signals easy. When the switch is in the OUT position, all
limiting and compression controls and fimctions are bypassed, with the
exception of the output control, which continues to function as a
straightforward level control. For all normal compress and limit functions,
this switch should be depressed to the IN position.

Threshoid/Gain Reduction Indicators

Five LED’s on the CL-50E and CL-100 front panels provide a convenient
visual indication of the amount of gain reduction that is taking place at any
time. As soon as the OdBV threshold level is reached, the yellow LED
illuminates. Depending on how far the input level rises above threshold, and

the settii^ of the RATIO, ATTACK, and RELEASE controls, successive red
LED’s will illuminate, indicating increasing gain reduction.

Gain reduction is a useful way of expressing compressor/limiter action.

We have seen that Ihe increase in output level of a compressor/limiter is less

than the increase in input level by some amount. Using a limit ratio, output
level will remain nearly constant as input levels increase above threshold.
Wth a gentle ratio, say

21, input signals above threshold will be “gain-

reduced” at the output by exactly 1/2. Ihus, gain reduction can be expressed
as input level increase divided by output level increase. For example, a +12
dBV input signal that is 3:1 compressed will produce 4 dB of change at the
output, and 8 dB of gain reduction has occurred (12 d£ input minus 4 dB
output = 8 dB gain reduction). The -6 dB red LED on the CL-50E or CL-100
front panel would be seen to lii^it up because we are past 6dB reduction, but
not jet to lOdB. □

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INITIAL SETUP AND CHECKOUT

Exact control of system headroom requires defining the clipping point of
the amplifiers in relation to the nominal zero VU of the mixing console. A
signal generator and oscilloscope would be helpful in determining this point
Since many people do not have the facilities or time to set up their systems in
this way, an alternate approach is suggested.
* First, realize that the sound system may have several different “0 dB"

levels, especially if equipment of different manufacturers are being mixed.
0 VU on the mixer’s meters may or may not correspond to a 0 dB V level of
.778 Volts. Also, note that input sensitivities of power amplifiers also vary.

1. Begin by turning the crossover level controls down.

2. Switch the unites LIMIT switch to the OUT position.

3. Set both the GAIN and OUTPUT level controls to 0 dB.

4. Set the RATIO control to 10 and adjust the ATTACK and RELEASE
controls to a relatively fast setting.

5. Plug a good quality music source into the mixing console and adjust

the console so that its meter peaks at around 0 VU.

6. Look at the LED display on the CLr50E and adjust the GAIN control

so that the yellow THRESHOLD LED lights only on peaks.

7. Note the new position of the GAIN control and adjust the OUTPUT
control inversely. That is, if you increased the Gain control to +10 dB

in order to light the Threshold LED, then decrease the Output control
to-10 dB. Or, if you had to decrease the Gain control to light the

Threshold LED, then increase the Output by an equal amount. You
have rww gotten the console and the compressor/limiter into relative
agreement over what is a maximum permissible signal level; as long
as the console’s output meter stays out of the red, little or no limiting

will occur. At or above console 0 VU, limiting will take place.

8. Turn the input volume control of your electronic crossover up to its
nominal zero point fforAshly crossooers this is it 7). Turn the

OUTPUT level controls of the crossover up until you achieve a good
musical balance of low and high frequencies, and continue to increase
the output volume controls until the soimd system just begins to sound
a little distorted. Since audible distortion may already be around 5%,
its a good idea to back off the output volume controls just a touch after

you first begin to hear any distortion. All elements of the sound system

are now in agreement. Console OVU - Limiter Threshold = onset of
clipping in your power amplifiers. If you wish to allow extra
headroom in the system between console OVU and the onset of
dipping, turn down the ClrSOHs OUTPUT volume control by 5 dB,

10 dB, or whatever saftty margin you desire. (You can turn the music

down now.)

9. Start with alms. ATTACK time, a.5 sec, RELEASE time, and a
RATIO of 10. Adjust these parameters according to the type of
program material, and firmness of control desired.

10. Activate the compressor/limiter by depressing the LIMIT IN/OUT
switch. Now, bud bursts of energy above 0 VU will cause little or no
dipping in the system. □

THEORY

77ie Need For Gain Control

The human ear excels in its ability to detect an extremely wide range of
loudness levels, fix}m the quietest whisper to the roar of a jumbo jet. When
we attempt to reproduce this dynamic range, by means of amplifiers, tape
recorders, records, or radio transmitters, we run into one of the fundamental

limitations of these electronic media: limited dynamic range. Amplifier
dynamic range is quite good, and is adequate for most musical program
material. However, some types of audio equipment, such as cassette tape
recorders, have a very narrow useful dynamic range.

What is it that compromises the dynamic range of this equipment? The
useftil operating region of a piece of audio equipment is squeezed in between
noise and distortion. As program level decreases, it approaches what is
known as the “noise floor”, and if the volume of the program material goes
lower still, it is engulfed by the noise. The noise floor, or minimum constant

noise level, will consist of hiss, hum, transistor noise, record scratches, tape
hiss, buzz and whatever noises are inherent in the medium. When the
program level is considerably higher than the noise floor, our hearing masks
the noise, and it is not a problem. However, when listening to very quiet

sections of a program for example, a pause between movements of a string
quartet the noise can become very bothersome.

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