Another highly useful features of the 543 is the Peak / RMS mode, which allows the VCA to respond to both RMS (Root Mean Square) and peak levels. RMS circuits are considered to better mimic the way the ears perceive apparent loudness, while peak circuits tend to directly respond to the waveform voltage, which may be more of a concern for prevention of clipping and maximizing levels.
In the case of this particular circuit, peak mode actually uses a combination of both methods to get the best of both worlds, and avoids the drawbacks of each method on its own.
THRESHOLD
Controls when the compressor begins to react from -30 dB to +20 dB. When set to +20 dB minimal to no compression is applied and and more gain reduction as the knob is rotated towards -30 dB.
RATIO
Controls the “slope” of the compression from 1.1:1 (minimal) to 40:1 (Limit). In general, low ratio settings apply more subtle compression while high ratio settings can be more effective at preventing unwanted clipping.
COMP IN
Illuminated push-button switch that engages the compressor.
F/F + F/B
Push-button switch that toggles between two different compressor modes, FEED FORWARD and FEED BACK. The F/B mode (button in) tends to sound smoother and more natural. The F/F mode can be more useful for shaping the envelope of the sound and introducing more ‘pumping’, if desired.
MAKE-UP GAIN
Continuously variable control for the make-up gain of the compressor within a range of -6 dB to +20 dB.
ATTACK
Controls how quickly the compressor reacts and starts attenuating. Continuously variable within a range of 20mS to 75mS.
RELEASE
Controls how quickly the compressor stops applying gain reduction. Continuously variable within a range of 100mS to 2.5 Seconds.
RMS/PEAK
Push-button switch that toggles between the compressor responding to the RMS level of the audio or responding to the PEAK level. RMS (root mean squared) more accurately mimics the way the ears perceive apparent loudness, while PEAK directly responds to the waveform voltage, which may be more useful to prevent clipping and maximize levels.
S/C HPF
Push-button switch that engages the high pass filter (fixed at 250Hz) for the side chain of the compressor. Please note that the high pass filter is not applied to the main audio output, this only adjusts the frequency range of the signal being compressed..
LINK
Switch that engages the stereo compressor link mode, linking the gain reduction circuits to work in tandem.
GAIN RANGE
Continuously variable from -6 dB to +20 dB
THRESHOLD RANGE
Continuously variable from -30 dB to +20 dB
RATIO RANGE
Continuously variable from 1.1:1 to Limit (40:1)
ATTACK RANGE
Continuously variable from 20mS to 75mS
RELEASE RANGE
Continuously variable from 100mS to 2.5 Seconds
TOTAL HARMONIC DISTORTION AND NOISE
@ 1 kHz, 0 dBu output level, no load.
Main Output, compressor bypassed: Better than 0.002%
@ 20 dBu better than 0.0015%
Main output, compressor engaged: Better than 0.075%
NOISE
Measured at Main Output, un-weighted, 22 Hz - 22 kHz, Terminated 50 Ohm. Noise specifications may vary depending on which 500 series chassis is being used, and / or interference from stray magnetic fields.
With Gain at Unity, Compressor disengaged: Better than -98 dBu
With Gain at Unity, Compressor engaged: Better than -93 dBu
FREQUENCY RESPONSE
Main Output, Unity Gain: @ 150 kHz -3 dB
METERS
For monitoring OUTPUT LEVEL and GAIN REDUCTION
LINE INPUT IMPEDANCE
10,000 Ohms
MAXIMUM OUTPUT LEVEL
21 dBu from 20 Hz to 40 kHz
POWER REQUIREMENTS
500 series rack with 110-125 mA @ +/- 16V
UNIT DIMENSIONS
1x 500 Series Module: 1.5” W x 5.9” D x 5.25” H
(3.8 cm W x 15 cm D x 13.3 cm H)
UNIT WEIGHT
1.5 lbs. (0.7 kg)
SHIPPING DIMENSIONS
10” W x 8” D x 3” H
(25.4 cm W x 20.3 cm D x 7.6 cm H)
SHIPPING WEIGHT
3 lbs. (1.4 kg)
