The JOEMEEK SC4 is a stereo compressor with a unique adaptation of M&S recording techniques to guarantee perfect image accuracy even when optical compression might misbehave.

he SC4 Is basically a Joemeek SC2 stereo compressor with additional features. The analogue inputs are balanced via XLR connectors, at line level, and the input gain control can add gain up to a limit of 18 dB. After the input stage, the audio is converted to 'middle and side' mode, this means that one channel contains the 'volume' (sum) information, while the other contains the 'width'(difference) information. A front panel switch disables the MS coder so that either analogue or digital signals in MS mode can input directly.

On the rear panel two jack sockets give insert access to the 'middle' and 'side' audio signals. This is so that special effects can be introduced by processing the width information independently of the volume information. The signals go through the compression circuits where a non-linear sidechain drives light sources, and the actual compression is done with photo-resistors. This is the heart of the Joemeek sound. Because of the difficulties in achieving a true hard-wired 'bypass' switch (especially with digital), the 'compression in/out switch has the additional facility of switching in extra gain to allow for the compression effect. Although the amount is only 2dB, this makes the comparison 'compressed/uncompressed' switch very much more useable.

Metering is unconventional: The left hand meter reads the volume information in the stereo signal, the right hand meter reads the compression depth in real time. After compression, the 'side' channel goes through a separate variable amplifier giving a 'width' control. This affects the stereo image so that it is variable all the way from 'mono' out to 200% stereo. A detented output gain control is calibrated to give 6dB gain in hand and the MS signal is then decoded back into stereo left and right. The analogue output stage gives balanced outputs via XLR connectors.

Digital inputs are either optical or AES/EBU, at 44.1 or 48 KHz samplerate. Digital to analogue conversion is to 24 bit standard. The input to the compressor section is switchable between the analogue inputs and the digital inputs.

After compression and the analogue output gain control, the decoded audio signal drives both the analogue output stages, and the analogue to digital converters. The clocking of the digital output is selectable: A 'local/remote' switch selects whether the output follows the incoming clock or generates a local clock.

Another select switch determines the local clock setting; 44.1 or 48KHz. LEDs show the selected samplerate but they are only illuminated when the selector is in 'local' mode, or when there is no incoming clock. When an incoming clock is present, it is indicated by a red LED on the front panel.

Digital outputs are AES/EBU and optical (SPDIF) with an additional pushbutton on the rear panel which switches 'consumer' or 'professional' mode.

ANALOGUE INPUTS
Line inputs are 20Kohm floating balanced via XLR connectors maximum level is approx +28dBu.

ANALOGUE OUTPUTS
Line outputs are XLR connectors 75 ohm source impedance, auto-centreing balanced. Maximum output +26dBu.

INSERT 
An unbalanced port is provided so that additional analogue circuits may be inserted into the sum and difference (MS) path. 
The 'tip' is the buffered analogue output of the MS coder the 'ring' is the input of the compressor

DIGITAL INPUTS AND OUTPUTS
All digital connections DC isolated from analogue systems. 
TOSLINK Optical inputs and outputs. 
AES/EBU XLR input and output.

POWER 
Power input is 230 or 115VAC at approx 12 watts. Voltage selection is by rotating the fuseholder. NOTE. Operation of the compressor on the wrong mains voltage WILL CAUSE TERMINAL DAMAGE.

TECHNICAL SPECIFICATION

ANALOGUE SIGNAL PATH

INPUTS : XLR connectors. Floating electronic balanced inputs 20Kohm impedance.

INSERT : unbalanced 1/4 inch jack.10Kohm nominal -10dB. source impedance 400 ohms.

OUTPUTS : Main analogue outputs XLR connectors. Auto centering electronic balanced. Source impedance 75 ohms.

AUDIO PERFORMANCE

AMPLITUDE FREQUENCY RESPONSE : +0 -1dB 7Hz to 30KHz (analogue path) +0-1dB 10Hz to 20KHz digital path.

HARMONIC DISTORTION : less than 0.01% at all frequencies and levels except under compression where 2nd harmonic distortion is generated by the compression.

MAX. OUTPUT : +26dBu

NOISE : less than -84dBu (dynamic range exceeds 110dB)

DIGITAL SIGNAL PATH .INPUTS AND OUTPUTS (optional on some models)

AES/EBU and TOSLINK OPTICAL.

CONVERSION PERFORMANCE : A/D 1 bit system producing 24 bit word at 128 times oversampling. D/A 24 bit word capacity. 128 times oversampling. Analogue performance limited at high frequency by sample rate. At 48KHz, system is 1 dB down at 22.5KHz.

Dynamic range capability : 115dB.

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