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720
/ 722 Dominator II Precision Multiband Peak Limiter |
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The
Aphex Systems Model 720 / 722 Dominator II is
a stereo MultiBand peak limiter designed to
fit a wide range of applications. Through the use of MultiBand
techniques along with new proprietary circuits, the audibility
of limiting action has been greatly reduced, especially when
compared to conventional limiters. This means that greater limiting
depth is possible, resulting in higher loudness with maintained
audio quality. At virtually any limiting depth, the Dominator
II is free of "hole punching", "dullness",
and most other effects normally associated with limiters. As
a peak overshoot protection limiter, the Dominator II is undetectable
in line while it absolutely prevents peak levels from exceeding
a user settable output level. In addition, the desired limiting
effects of greater audio density and increased "punch are
readily available with the Dominator II.The Model 722, for broadcast
use, has the Pre and De-emphasis circuitry, while the Model
720 does not. |
| FEATURES |
| • |
Peak
Ceiling Trimmable in 0.2dB Steps Over a 34dB Range |
| • |
3
Bands of Limiting with Switchable Crossover Frequencies |
| • |
Patented
Automatic Limit Threshold (ALT) Circuitry |
| • |
Freedom
from Pumping |
| • |
Freedom
from Spectral Gain Intermodulation |
| • |
Adjustable
Density (Relative Crest Height) |
| • |
Calibrated
Detented Potentiometers |
| • |
104dB
Dynamic Range |
| • |
LF and HF EQ Provides Shaping Equalization Below Peak Ceiling
|
| • |
Relay
Bypass, Remote Controllable |
| • |
Servo-Balanced
Transformerless Inputs and Outputs |
| APPLICATIONS |
| • |
Sound
Contracting -- protection of amplifiers and speakers from overload;
increased loudness; maximized use of available power. |
| • |
Recording
-- preventing sudden peak overload of mixer or recorder; tightening
tracks; special effects, etc. |
| • |
Mixing
-- used as a program limiter, the Dominator II will keep a track
"rock steady" for "layering" into or on
top of a mix. |
| • |
Digital
Sampling -- obtaining good full scale samples free from peak
overload, i.e. no more missed samples. |
| • |
Digital
Recording -- insuring clean recording by stopping clipping of
peaks and overshoots. Maximizes bit usage for less distortion.
|
| • |
Satellite
Uplink -- Modulation control to prevent splattering on high
frequency audio, gives reduced distortion, better signal-to-
noise. |
| • |
Broadcasting
-- AM and FM modulation control for increased loudness; cleaner
sound; use in production for greater consistency of tapes, punchier
voice-overs. |
| • |
Location
Film Shoots -- anti-crash for dialog and sound effects recording.
|
| • |
Post
Production -- Soundtrack peak control; managing difficult dialog;
controlling transient sound effects. |
| • |
Optical
Recording and Transfer -- prevents "valve clash",
gives higher average level with low distortion and better signal-to-
noise performance. |
| • |
Analog
Disk Mastering -- peak control for high allowable average cutting
levels; less limiter degradation to the program; brighter, punchier
sound. |
| • |
C/D
Mastering -- peak and density control for more accurate digitizing,
cleaner sound requiring less error correction on playback; no
limiter induced sound degradation. |
| • |
STL
& Phone Line Driver -- maximize signal-to-noise without
overload distortion. |
| • |
Video
and Audio Tape Duplication -- "Hotter" transfers without
saturation. |
| Multiband
vs Wideband Processing |
A
very significant problem with wideband processing is "spectral
gain intermodulation" which occurs when one part of the
spectrum controls the level of another part. A typical situation
is a vocalist being "sucked down" every time the kick
drum hits.
Since most energy is contained in the lower frequencies, they
tend to control the level of the entire spectrum. When the lower
frequencies are above the limit threshold the higher frequencies
are attenuated thus 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 giving the
user flexibility, it also requires different settings for almost
every different source.
The
Dominator II uses program dependent, intelligent circuits to
reduce the number of controls. The user, therefore, has flexibility
to shape the sound while quickly and easily achieving the goal
of consistent, effective limiting. |
| ALT
(Automatic Limit Threshold) |
A
MultiBand processor splits the audio into separate bands, limits
each band individually and 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. This, however,
introduces all the drawbacks of wideband limiting discussed
above.
Another
approach is to use a clipper on the summed output. This causes
too much clipping distortion if the summed output is too high.
In order to avoid this distortion the limiters' thresholds are
set very far below the clipper threshold. The drawback is a
loss of loudness and, due to the lower thresholds, much greater
amount of processing.
The
Dominator II uses a patented method to produce a predictable
peak output while maintaining maximum loudness without audible
distortion- the Automatic Limit Threshold (ALT). The outputs
of the three bands are summed and sent to the ALT detector circuit.
If the sum exceeds a reference value, the ALT 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.
Both
parameters are set by the Density control. When the Density
control is set higher, the ALT reference gets closer to clipping,
and the attack time is slower, producing more clipping. The
opposite occurs when Density is set lower. The "0 RCH"
position for the Density control emulates the standard parameters
of the original Studio Dominator Model 700, and is recommended
for general use.
It
should be noted that there is only one ALT circuit controlling
both channels equally. This provides global stereo balance and
imaging by assuring that both channels always limit at the same
threshold. This does cause an interaction if the Dominator II
is used as two independent channels. Therefore, we do not recommend
such a practice. |
| Model
722 Pre- and De-emphasis |
Pre-emphasis
is an equalization curve expressed as a time value based on
the ratio of a resistor and capacitor. The higher the value,
the greater the equalization. It has been employed as a noise
reduction technique for broadcast and transmission links. There
are primarily two world standards- 50 and 75 microseconds.
The Dominator II Model 722 has separately switchable pre and
de-emphasis curves. When pre-emphasis is switched in, either
50 or 75 microseconds, the equalization curve is added after
the input stage and before the limiters. When de-emphasis is
switched in, the complementary de-emphasis curve is inserted
after the final clipper and before the output stage.
When both pre and de-emphasis are switched in, the frequency
response of the output is flat. When the input is below threshold
and as the input increases above threshold the output takes
the shape of the de-emphasis curve. When
both pre and de-emphasis are switched out, the Model 722 works
exactly like the Model 720.
|
| Aphex
Dominator II Models 720 / 722 Block Diagram |
|
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| Using
the Aphex Model 720 / 722 |
| 1 |
INPUT
Adjusts input level ±15dB. Center detent is unity gain.
|
| 2 |
PROCESS
IN / OUT Switches the audio through the unit or through bypass
relays. |
| 3 |
LF
EQ Adjust input level to the low frequency band ±5dB.
Center detent is "flat" response below limiting. |
| 4 |
LF
XOVER Switches the crossover point between low and mid bands
from 100Hz to 210 Hz. |
| 5 |
HF
EQ Adjusts input level to the high frequency band ±5dB.
Center detent is "flat" response below limiting. |
| 6 |
HF
XOVER Switches the crossover point between mid and high bands
from 1.7 kHz to 3.4kHz. |
| 7 |
RELEASE
TIME Adjusts release time of the limiters between 150 msec (fully
Clockwise) and 7 seconds (fully Counter-clockwise) |
| 8 |
STEREO
COUPLING Forces the limiting in each band to be equal to the
limiting in the same band of the other channel if the band in
the other channel has a greater amount of limiting. |
| 9 |
DENSITY
Adjusts the RELATIVE CREST HEIGHT (RCH) of the output. The higher
the RCH (Clockwise) the louder the output. The lower the RCH
(Counter clockwise) the lower the average level output. |
| 10 |
FINE
Adjusts the peak ceiling by ±1dB in .2dB steps. |
| 11 |
RANGE
When switched to the "-10" position it adds a 10dB
boost to the input and a 10dB cut in the output. The PEAK CEILING
is therefore 10dB lower than the settings shown on the "COARSE"
and "FINE" controls. |
| 12 |
METER
Displays the limiting (from gain reduction and clipping) in
the channel with the greatest amount of limiting. |
| 13 |
POWER
Switches AC mains on and off. In the "Off" position
the audio signal is hard-wired bypassed through bypass relays.
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| FRONT
PANEL VIEW, CONTINUED >
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SPECIFICATIONS
- Aphex Model 720 / 722
Precision MultiBand Peak Limiter |
| RANGE SETTING: |
0dB |
-10dB |
| Audio |
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| |
Frequency
Response |
±0.5
dB 10Hz to 50 kHz |
same |
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Nominal
Gain |
0dB
+14dB / -21dB |
0dB
+8dB / -21dB |
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Signal/Noise
(Ref +4dBm) |
-84dB |
-94dB |
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THD
(Ref 1kHz, no limiting) |
<0.006%
(+12dBu in) |
<0.006%
(+2dBu in) |
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SMPTE
IMD |
<0.006% |
<0.006% |
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Max
Input (MIL) |
+26dBu |
+16dBu |
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Max
Output Level (MOL)* |
+24dBm
Peak |
+14dBm
Peak |
| *(MOL is limite
,.d by the peak ceiling setting. The output stage
is capable of +25dBu into 600 ohms) |
| |
Crosstalk |
-60dB
up to 10kHz |
same |
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Dynamic
Range |
104
dB |
same |
| Inputs
and Outputs |
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Input
Circuits |
Servo
Balanced Transformerless |
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Output
Circuits |
Servo
Balanced Transformerless |
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Input
Connectors |
3-pin
XLR Female |
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Output
Connectors |
3-pin
XLR Male |
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Input
Impedance |
19.5k
ohms unterminated; 600 ohms by rear panel switch
(terminator lifts in bypass mode) |
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Output
Impedance |
65
Ohms |
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Input
CMRR |
Better
than 50dB 20Hz to 20kHz |
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Input
RF Rejection |
Better
than 40dB at 800kHz; better than 60dB above 2 MHz |
| Controls
and Adjustments |
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Input
Gain |
+14dB
/ -21dB |
+8dB
/ -21dB |
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LF
EQ |
±5dB |
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LF
Crossover |
100Hz
/ 210Hz |
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HF
EQ |
±5dB |
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HF
Crossover |
1.7kHz
/ 3.4kHz |
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Release
Time |
150msec
to 7 seconds |
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Density |
-5
to +5 RCH |
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Output
Ceiling |
-9
to +24dB (peak) (=peak value of sinewave) |
| Other
Specifications |
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Power
Requirements |
120
VAC 50-60 Hz 30 Watts (100, 220,
240 options) |
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Power
Fuse |
100/120
VAC = .375A SloBlo; 220/240 VAC = .25A SloBlo |
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Dimensions |
19"W
x 1.75"H x 9.5" D (482.6mm x 44.5mm x 241.2mm) |
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Net
Weight |
9
lbs (4.08 kg) |
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