Clean, precise, powerful level control
Whether you're tracking, mixing or mastering, the 543 delivers unobtrusive, musical dynamic control and high-ratio limiting with massive flexibility, transparency and precision.

The 543 features a fully controllable compressor-limiter with feed-forward / feedback modes, Peak / RMS detection and a built-in side chain high pass filter. With an unrivaled heritage and a tremendous feature set, the 543 provides an astonishing degree of flexibility and precision.

Features:

- Unobtrusive, musical dynamic control
- High-ratio limiting with massive flexibility, transparency and precision
- Feed-forward / feedback modes
- Peak / RMS detection
- A built-in side chain high pass filter
- Low noise, low distortion VCA (Voltage Controlled Amplifier / Attenuator)
- Immense amount of dynamic control and subtle warmth
- Doesn't leave a heavy sonic imprint

What is VCA compression?
Every compressor has a gain control element in its circuit, and this is generally what determines the "sound" of the compressor. Some compressors use tubes, some use FETs, some use light-dependent resistors, some use a diode bridge - but in the 543, a VCA (Voltage Controlled Amplifier / Attenuator) is used to control the signal's gain.
In contrast to a diode bridge design like our 535 compressor, which adds a thick, very colorful tonality to the source, the 543 makes use of a very accurate, low noise, low distortion VCA. This provides an immense amount of dynamic control and… read more subtle warmth, without necessarily leaving a heavy sonic imprint on your tracks or mixes.

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

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