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SSL XLogic G-series Compressor

Dynamics Processor
Published February 2006
By Hugh Robjohns

SSL XLogic G-series CompressorPhoto: Mike Cameron

The celebrated mix-buss compressor design from the G-series consoles has been brought up to date using SSL's latest Superanalogue circuitry.

The Oxfordshire-based company Solid State Logic — SSL to their friends — have been at the cutting edge of analogue mixing-console design for many decades, and have recently also branched out into rackmount processing. I reviewed their XLogic Superanalogue Channel back in SOS February 2005, and its sibling is now under review here: a high-quality stereo mix compressor derived from that first seen in the centre section of the G-series consoles, but improved using their latest Superanalogue circuitry.

Construction & Controls

The unit is housed in a 1U rackmount case which extends 325mm behind the rack ears. Two pairs of XLRs on the rear panel supply balanced stereo line I/O, and a further female XLR offers an external key input. A recessed switch isolates signal and chassis earths if necessary, and the IEC mains inlet incorporates a fuse holder which can configure the operating voltage for different regions. Construction is to exceptionally high standards, with very neat and safe wiring.

The classic functional styling of the front panel makes it easy and quick to use, with simple controls providing all the essential parameters, and a traditional moving-coil gain-reduction meter indicating up to 20dB of attenuation. The first of the six rotary controls adjusts the threshold continuously from -15dBu to +15dBu. The next three are rotary switches, providing attack times of 0.1, 0.3, 1, 3, 10, or 30ms; ratios of 2:1, 4:1, or 10:1; and release times of 0.1, 0.3, 0.6, or 1.2s, or an automatic release mode. The continuously variable Make-up knob spans -5dB to +15dB, and large illuminated buttons activate the compressor circuitry, the external side-chain key input, and the separate Autofade facility. The final rotary control adjusts the fade time from 1s to 60s.

Circuit Design

Although the controls are very simple, there are a number of clever things going on 'under the bonnet' here. The first thing to mention is that the Compressor In button normally provides a 'soft bypass' which just forces the gain-reduction circuitry to provide unity gain. However, internal circuit jumpers allow a 'hard bypass' to be selected instead, in which case four sealed changeover relays connect the inputs directly to the outputs — the disadvantage being that you can't then use the Autofade function if the compressor is bypassed.

SSL XLogic G-series CompressorPhoto: Mike CameronAnother nice touch is that the Autofade circuit generates a control voltage that, rather than being linear, replicates the audio taper of a real fader, so that the slope gets steeper towards the bottom of the fade, and sounds more natural, especially with longer fade times. The Autofade feature can be controlled remotely through the rear-panel nine-pin D-Sub connector, and you can also connect up an external gain-reduction meter to mirror the display of the unit's internal meter.

Analogue Warmth?

The XLogic series all get quite warm in use, largely because of the current demands of the Superanalogue circuitry. The G-series Compressor is no exception, and it is well worth heeding the handbook's warnings about leaving 1U of rack space above the unit, and about not placing it above anything else hot.

While on the subject of handbooks, The Owner's Manual supplied with the G-series Compressor is a classic for 'tech heads'. After some perfunctory operational instructions and technical specifications, you quickly find yourself amidst fairly detailed technical descriptions of how the circuitry works, complete with full circuit diagrams — proper engineer's stuff, but not perhaps of much help to anyone struggling to understand what the Attack control does!

Plugging the G-series Compressor in is simple enough, with nominal +4dBu balanced signals in and out. The unit has a maximum output level of a healthy +24dBu, so there shouldn't be a problem feeding digital mastering recorders directly from the output if required. Achieving a suitable setting is as intuitive as selecting the required ratio, dialling up the Threshold to achieve the amount of 'squash' needed, and then fine-tuning the Attack and Release controls to optimise the sound character.

Like the mix compressor from which it is derived, this XLogic unit does a great job of making any mix sound louder, but without becoming aggressive or obvious about it. The automatic release mode was rarely caught out (so I tended to leave it set in that mode), while the ability to fine-tune the Attack time to suit the material was sometimes very useful indeed. Although you only get three ratios, you won't want any more: the 2:1 setting introduces relatively subtle and transparent control, the 4:1 mode is a little harder and more obvious (but in a good way!), and the 10:1 mode is essentially peak limiting, which can be used either to keep a wary eye on any unruly transient peaks, or to squash the sound to death in those circumstances where that might appeal!

The Autofade facility is something I've never personally felt the need for — I like to pull the main fader up or down by hand. But where you want consistency of fades across several versions of a mix it can be used to advantage — assuming that you hit the button at the same point in the track each time, of course! The attenuation law sounds natural for the vast majority of mixes, although I did find that I could achieve more pleasing fades manually with some material.

Most studio engineers look upon the SSL console mix-buss compressor as an essential tool of the trade, and having access to one in a stand-alone box, with the added sonic benefits of the SSL's Superanalogue topology, is a masterstroke. If you are looking for a simple but very effective master stereo compressor, built to exemplary standards, then you can't go far wrong with the SSL pedigree. 

Published February 2006