Aphex Dominator II User manual

DOMINATOR II
PRECISION MUL TIBAND
PEAK LIMITER
OPERATING GUIDE
APHEX SYSTEMS, LTD.
11068 Randall Street, Sun Valley, CA 91352 [phone]

WARNING
TO REDUCE THE RISKS OF FIRE OR ~LECTRIC
SHOCK, DO NOT EXPOSE THIS APPLIANCE TO
RAIN OR MOISTURE

Dominator II
Errata And Modifications To The Operating Guide
Due to circuit changes, several parts of the manual are now
irrelevant or inaccurate. Please Note the followi~q changes.
~. section 3.0, Basic Setup, paragraph (5.) should read thusly:
5) Feed speech or music program at normal level; adjust ZNPUT
control to generate at least 6 to adB of limiting. Do not use
a steady tone for this purpose but a 1KHz tone burst with
30msec on and 300msec off may be used.
2. section 5.8.2, ALT Generator:
The circuit revision defeats the tone detector function and
places a direct connection from collector to emitter of Q3.
Therefore, any discussion of the tone detect circuit is
irrevelant. All discussion including Q3 should be taken to
assume Q3 is always conducting. The Dominator II no longer
recognizes test tones.
3. The parts list should be updated to reflect several new
values. .
Main Audio PCB:
R317(L,M,H)
was
10KO
is now 4K99
R417(L,M,H)
was 10KO is now 4K99
D301(L,M,H)
was
1N914B diode
is now
D401(L,M,H)
was 1N914B diode
is now
Aux
Control PCB:
C6 was O.OOlUF is now O.OlUF
R32 was 4K99 is now lOOK
5.6meg
resistor
5.6meg resistor

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DOMINATOR II
PRECISION MULTIBAND PEAK LIMITER
1.0 INTRODUCTION
After its introduction in 1985, the Studio Dominator became the
world standard for peak limitin.g because of its transparency and
effectiveness. However, un willing to rest on its already established
reputation, Aphex Systems. Ltd, has continued to develop new
techniques. The result is the Dominator II.
As a direct descendant of the original, the Dominator II has the
same primary functions and applications. Its many performance
improvements lie in the areas of dynamic range, distortion,
flexibility I and ease of setup.
Although those familiar with the Studio Dominator already know
much of the information in thls manual, Aphex recommends that
these people as well as those new to Aphex Dominators read this
manual.
The Dominator II is a stereo multiband peak limiter with absolute
zero overshoot. Once the PEAl{ CEILING is set. there is no
higher amplitude in the output. Awareness of headroom limitations
and the price of exceeding those limitations I important for any
audio application, is critical for most. especially digital. The
Dominator II allows users to work confidently I creatively. and
quickly by freeing them from the fear of "crashing".

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Achieving this brick wall result while retaining complete fidelity
is the art and science of the Dominator II. Because of its
exceptional function and performance, it has applications in a great
many audio fields, including:
. BROADCASTING-PRODUCTION, AND TRANSMISSION FOR AM.
FM.
AND TV
_RECORDING
_SAMPLING
.MIXING
_ MASTERlNG-CD. FILM, AND ANALOG DISK
_ SOUND REINFORCEMENT
. SATELLITE AND STL UPLINK
.LOCATION RECORDING
_VIDEO POST-PRODUCTION
. TAPE DUPLICATION
_TELECONFERENCING
1.1 DYNAMIC RANGE CONTROL
Essential to a full understanding of the operation and application of
the Dominator II is a knowledge of the definitions and applications
for each type of gain control: leveling, compression. limiting, and
clipping.
1.1.1 Leveling
Leveling has high compression ratios with slow attack and release
times. Because of its very slow time canstan ts, leveling has no
effect on short term changes in average levels or on transient peaks.
Therefore, it is used to maintain a constant output level without
affecting the short term dynamics by adjusting for long term changes
in the input signal. Typically. the threshold is set low so that low
level signals will be brought up.

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1.1. 2 Compression
Compression has low ratios with faster attack and release times. A
compressor forces a wide dynamic range into a smaller range. The
size of the resultin g dynamic range depends on the level of
the threshold, the height of the ratio used, and the speed of the
attack and release. The higher the ratio and the faster the time
constants, the greater the effect on the short term dynamics (the
actual quality and fidelity of the sound); these effects are often
used creatively. Normally, since one of the desired results of
compression is to bring up low level signals, the threshold is set
low.
1.1. 3 Limiting
Limiting has high compression ratios (usually defined as greater than
8:1), fast attack and, depending on the particular application and
desired sound, slow or fast release times. Since it is normally used
to keep high levels down, the threshold is set high. Inasmuch as
the ratios are high, as the input is driven further into limiting, the
dynamic range of the output becomes 'tighter', an effect that may
or may not be desirable. If the attack times are set to control only
the average level, and allow for peaks above the threshold to pass I
the limiter is considered a program limiter. When the speed of the
attack times is increased to control peaks, the limiter is considered
a peak limiter.
1.1.4 Clipping
Regardless of a limiter's attack time I there is a finite amount of
time before the detector circuits cause the gain circuits to reduce

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the output below threshold. Also, extremely fast gain modulation
introduces unwanted audible effects. Therefore, clipping with its
infinite ratios and instantaneous attack and release, functions as an
absolute brick wall. To control the pBaks, clipping literally shaves
off the peaks of the wave above threshold without changing the
amplitude of the remainder of the wave. Done properly, clipping
is inaudible and. under certain circumstances, actually enhances the
audio. Done improperly, however, clippin g produces very audible.
obnoxious effects.

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2.0 FUNCTIONAL DESCRIPTION
Traditionally, peak limiters have been designed with fast attack
times: the faster the attack time, the lower the amount of overshoot
above threshold. The drawback to these fast attack times I however,
is that the limiter is triggered off each transient, even extremely
short ones. The sonic result is hole punching and · overall lower
density (peak to average ratio). On the other hand, while slower
attack times result in better sonic performance, the overshoots
cause distortion, or the overall level must be reduced to accommodate
the overshoots. The Dominator II overcomes both drawbacks by
combining limiters with fairly slow attack times and clipping, in an
interacti ve, self-adjusting manner.
The Dominator II has been designed as a unity gain device with an
adjustable threshold. Since there is zero overshoot over threshold,
users have only to set the PEAK CEILING to the level at which
peaks must stop (fDr example: 100% modulation). In other words,
set it and forget it!
2.1 MULTIBAND VERSUS WIDEBAND PROCESSING
A significant problem with wideband processing is "spectral gain
iotermodulation" which occurs when one part of the spectrum
controls the level of another part. A typical situation is a vocalist
being 'sucked down' whenever the kick drum hits.

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Since most energy is contained in the lower frequencies, they tend
to control the level of the entire spectrum. When lower frequencies
are above the limit threshold, higher frequencies are attenuated,
causing the output to be dull.
Multiband processing solves these problems by splitting the audio
into two or more frequency bands, and processing each band
separately. However, more bands often result in many more parameters
to control, including a method of summing the bands together again.
While this creates user flexibility, it also requires different settings
for alrnost every differen t source.
Since the Dominator II uses program dependent. intelligent circuits
that reduce the number of controls, users have the flexibility to
shape the sound while quickly and easily achieving consistent,
effective limiting.
2.2 ALT (AUTOMATIC LIMIT THRESHOLD)
[Reference: Fig. 2.1 ALT BLOCK DIAGRAM, Page 2-4] _ A multiband
processor splits the audio in to separate bands, limits each band
individually, an d then sums the bands together again. Even though
each band's peak output is predictable, summing the bands together
produces an unpredictable peak output.
One conventional approach to making the summed output predictable
is to use a wideband limiter after the summing. Unfortunately, this
introduces all the drawbacks of wideband limiting identified above.

2-3
Another approach is to use a clipper on the summed output, but
this causes too much clipping distortion if the summed output is too
high. To avoid this distortion, the limiters· thresholds are set very
far below the clipper threshold. The drawback to this approach
1s a loss of loudness and, because of the lower thresholds, a rouch
greater amount of processing.
Instead of either of these approaches, the Dominator II uses a
patented method to produ~e a predictable peak output while
maintaining maximum loudness without audible distortion: the
Automatic Limit Threshold (AL T). With this method. the outputs of
the three bands are summed and sent to the AL T detector circuit.
If the sum exceeds a reference value. the AL T reduces the thresholds
of the individual limiters, When the summed output falls below the
reference value, the limit thresholds return to their original
setting.
The ALT circuit has a self-adjusting finite attack time. The amount
of time it takes to lower the thresholds of the limiters is the length
of time the limiters· overshoot may be in the clipper. The reference
value of the ALT in relation to the clipper determines the depth of
clipping. The DENSITY control sets both parameters. When it is set
higher, the ALT reference gets closer to clipping and the attack
time is slower, producing more clipping. When DENSITY is set
lower. the opposite occurs. The 0 ReR position for the DENSITY
control emulates the standard parameters of the original Studio
Dominator, Model 700; this is recommended for general use.

2-4
It is important to know that because there is only one ALT circuit
controlling both channels equally t this method provides global stereo
balance and imaging by ensuring that both channels always limit
at the same threshold. Since this does cause an interaction if the
Dominator II is used as two independent channels, Aphex does not
recommend such a practice.
"PEAK CEILING"
LIMITERS
BAND 2
DC THRESHOL REF
ALT BLOCK DIAGRAM
FIGURE 2.1
2.3 EQUALIZATION
As indicated above, wideband limiting often causes dullness. To
prevent this, a common practice is to follow the limiter with an
equalizer set to boost the high frequencies. The drawback is that
the equalizer adds directly to the overshoot.

2-5
Another practice is to attenuate the lower frequencies fed to the
detector circuits. While this diminishes spectral gain intermodulation,
the drawback is that when there is substantial energy in those lower
frequencies, it creates unacceptable amounts of overshoot.
The Dominator II eliminates these problems by using three-band
processing with selectable crossover frequencies between low and
mid-band and between mid and high-band, with adjustable input levels
to the low and high-band. Also. the crossover filters are designed
so that when the EQ controls are set flat and the input is below
threshold, the Dominator II will pass perfect square waves. This
means that the Dominator II equals a well designed wideband limiter
in below threshold audio performance, and vastly outperforms any
wideband device in performing its function above threshold.
The selection of the crossover frequencies and the input level to
each band helps determine the frequency response of the output.
When the input is below the limit threshold. the EQ will give a
response equal to the change in input in each band. Since the
compression ratio of the limiter is essentially infinite, a change in
the input level above threshold will not cause any change in the
output level. The EQ provides user flexibility to shape the sound
and still maintain an absolute peak ceiling.
2.4 RELEASE TIME
The release time allows users to adjust the density of the output.
With faster release times, the output is consistently maintained as
close as possible to maximum. Extremely fast release times result

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in a very tight dynamic range, and also may cause low frequency
distortion. Slower release times reduce the distortion and provide a
rounder, softer sound. Very slow release times tend to make the
output much lower in average amplitude, especially on transient
inputs.
2.5 GAIN CONTROL CIRCUITS
An important design goal for all Aphex products has been to make
a signal processor able to do nothing before it performs its
function. That is, it must be able to pass audio as if it were nothing
more than a straight wire--no noise, distortion, or color.
Essential to achieving that goal is the use of the Aphex VCA 1001 high
performance integrated gain control element. Its measured
specifications are outstanding as a signal amplifier, but even more
importantly, its dynamic performance surpasses all other devices.
Others produce distortion or amplitude anomalies with complex program
audio which do not appear with steady tone test measurements. Of
extreme importance is that other devices also create anomalies when
gain is changed rapidly. The best known anomaly is DC shift or
control feedthrough whose sonic results include clicks, pops, or
unintended signal fed to the control circuits. The Aphex VCA 1001
is completely free from these anomalies, even in the most demanding
situations such as a peak limiter.
Each band has its own limiter and detector. The attack time is
preset and equal for all limiters. The release time is adjustable and
also equal for all limiters. The threshold is adjustable from the

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front panel Peak Ceiling control and is also adjusted by the ALT.
2.6 TRACKING CONTROL
Tracking forces the limiting of each band in each channel to follow
the same band in the other channel. The channel with the greatest
amount of limiting will cause the same band in the other channel to
have an equal amount of limiting. This control maintains a stable
stereo image. Without the tracking control, increased stereo
loudness can be achieved but with potentially inaccurate or "smeared"
stereo imaging, depending on the amount of limiting. For light
limiting. non-tracking may be preferred in many cases.
2.7 DENSITY
The DENSITY control is one of the most important improvements
incorporated into the Dominator II. As indicated in section 2.2 ALT.
the DENSITY control adjusts the parameters of the ALT circuit. In
effect. this allows users to determine the RELATIVE CREST HEIGHT
(RCH) of the audio output signal. With a higher RCH setting. the
below-threshold peak levels increase, producing greater power in
the waveform as well as greater relative loudness.
By setting the ALT reference level and attack time. this control
essentially adjusts the average depth of clipping, and the relative
duration of cUpping allowed. High clipping depth and duration
create greater loudness, but may generate high distortion. Low
clipping depth and duration reduce clip distortion, transferring more
work to the limiters. Reduced loudness and 'punch' is traded for
low distortion.

2-8
For those interested in the technical aspects, when the DENSITY
control is in the 12 o'clock position, the limiter thresholds are 3dB
below the clipper threshold. Fully clockwise, the limiter thresholds
are at the same level. Fully counterclockwise, the limiter
thresholds are 6dB below the clipper.
2.8 PEAK CEILING CONTROL
Many audio applications require that the peak output be trimmed to
be as high as possible. To fulfill that requirement. the Dominator II
was designed with two controls for the output ceiling. The COARSE
control switches the ceiling, in 2dB steps. from +2 to +24dBu (peak).
The FINE control adjusts the ceiling +1 to -idB from the COARSE
setting. in O.2dB steps.
There is a third control, RANGE, which adjusts the internal gain
structure by adding lOdB at the input. and subtracting lOdE at the
output. These three controls give users the ability to trim the
peak output to within O. 2dE over a 34dB range.
The PEAK CEILING controls set the threshold of clipping (the
maximum peak output). If the input level remains below threshold.
adjusting the PEAK CEILING controls does not affect output levels.
2.9 INPUT AND OUTPUT CIRCUITS, BYPASS RELAY
For maximum audio performance. the Domina tor II has servo-balanced
transformerless audio I/O circuits. With these, perfect interfacing
with any system, balanced or unbalanced. high or low impedance.
is extremely simple.

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The input stage and AC power input receptacle include radio
frequency filtering to reject interference from transmitters and allow
the Dominator II to be used in typica~ broadcast racks.
The servo balanced input stage has a selectable 600 ohm termination
resistor for systems which need to be loaded. When Bypass mode
is selected. the resistor is lifted to prevent line loading disturbance.
For systems that don It require a load resistance J users simply do
not select the termination; unterminated. the input impedance is
19.5K-ohm.
The servo-balanced output stage properly drives any load of 600
ohms or greater. The output impedance of 65 ohms can drive
long capacitive lines effectively. terminated or unterminated. The
especially unique characteristic of the servo-balanced output stage
is its ability to drive balanced and unbalanced output lines without
difficulty. For unbalanced output, the unused output pin (2 or 3)
is GROUNDED to pin 1. This causes the output stage to shift all
drive automatically to the hot pin only. and adjust gain to provide
full output level (no 6dB loss as with other circuits).
A high quality audio relay provides a true hard-wired bypass function.
Bypass connects the output connector directly to the input connector
and lifts the input termination resistor J if it was selected. The
limiter input stage is still connected to the input connector; thus.
the limiter remains active for instant insertion in line. The Bypass
function can be initiated in one of three ways: powering down or
power failure; front panel Process Off/Oo switch; or remote control
(rear panel jack). This configuration provides a fail-safe

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characteristic for critical systems where the audio signal must be
bypassed through the Dominator II if the AC line or internal
power supply fails.
2.10 MODEL 723 PRE AND DB-EMPHASIS
Pre-emphasis is an equalization curve expressed as a time value based
on the ratio of a resistor and capadtor. The highsr the value, the
greater the equalization. This has been used as a noise reduction
technique for broadcast and transmission links.
Primarily, there are two world standards: 50 and 75 microseconds.
Starting flat at approximately 1KHz I 50 microsecond pre-emphasis
jncreases almost 12dB at 15KHz; 75 microsecond pre-emphasis increases
over 17dB at 15KHz.

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The Dominator II Model 723 has pre-emphasis (either SO or 75
microsec) added after the input circuit and before the limiters. It
also has a complementary de-emphasis circuit (which may be switched
out of circuit) after the final limiter and before the output stage.
When the de-emphasis circuit is in circuit. the audio output of the
Model 723 is flat if the input is below threshold. As the input
increases above threshold. the · output takes the shape of the
de-emphasis curve.