Field Test: Solid State Logic XLogic Multichannel Compressor

A 5.1 Unit With That Old Familiar Sound 5/01/2004 8:00 AM Eastern

Solid State Logic continues the modern tradition of large-consolemanufacturers by adding processor units to its inventory with thelatest release of the XLogic series, which employs the Grammy-winningSuperAnalogue technology introduced with the SL 9000 for excellentbandwidth and dynamic range, as well as surface-mount technology forcompact profiles.

XLogic modules include the XLogic Channel (with G and E Series“Twin-Curve” 4-band parametric EQ and optional 96kHz A/Dconverter), the XLogic G Series Stereo Compressor (a new version of anold favorite, with twin VCA design and auto-fade) and the XLogic4-Channel Mic Amp (a smaller version of XL9000's Super-Pre withmotorized control for mic gain that can be adjusted on the unit or viaremote). It also includes the SL944 remote (which can control two ofthe XLogic Mic Amps) and the answer to DVD multichannel audioengineers' prayers: the XLogic Multichannel Compressor.


Unless you're one of those audio engineers who has steadfastlyeschewed the center channel in favor of the retro “quad”version of surround, or one who refuses to recognize the frequent needfor the LFE in professional multichannel productions, you'llimmediately appreciate the flexibility and control offered by theXLogic Multichannel Compressor. It's the solution to the commonmultichannel mixing dilemma: how to maintain the bottom end whilecontrolling the center channel, without losing the total surroundsoundstage.

The XLogic Multichannel Compressor owes much of its heritage to thetraditional SSL mix bus compressor, but adds the XL9000's DC-coupleddesign, yielding better specs than older implementations. Looking underthe hood reveals 56 THAT 2181LA VCAs with trims for in-circuitadjustment for low distortion and excellent feed-through performance,as well as LT1115 op amps (touted as being the lowest-noise op ampavailable) and LT1010 buffers to increase op amp output and reducethermal feedback. There's also a turn-on relay to prevent audiothumps.

We measured 101 degrees with a probe over the vents of the unit inopen air with a room temperature of 71 degrees and the unit sitting onhalf-inch spacers with no heat-producing gear under it. If yourack-mount this box, heed the mounting instructions to leave onerackspace above it for ventilation.


The compressor provides a clean, clearly visible layout with thetraditional SSL square, lighted push buttons and the six-LED“Max” display, an alluring piece of eye candy that showschannel contribution status to the sidechain.

It can run in two modes — multichannel or dual-stereo —which allows it to function as separate 2- and 4-channel compressors.Dual-stereo mode reassigns controls so that the upper set governs left,center, right and LFE, and the lower set provides compression for thesurround channels.

An illuminated gain reduction meter is lighted by a ghostly whiteLED. Users can switch between monitoring the main 5-channel sidechainto monitoring either the LFE or stereo B sidechain, depending ondual-stereo mode status. Although the controls are well-defined, theengineer should keep in mind which channels are contributing to thesignal path and their allotted levels and behavior. Next to the meterare two compressor sidechain controls with In switches, and threshold,attack, ratio, release and makeup controls.

In multichannnel mode, the upper set controls the fivefull-bandwidth channels, while the lower set is assigned to the LFEchannel. This is the traditional multichannel mix setup, where the LFEis often used for sound effects that can push to maximum headroomallowance in a split second.

If the surround channels seem to be the problem area (oftenencountered in live or upmixed situations in which the audience isprimarily in the back), then you can switch to dual-stereo mode so thatthe lower sidechain controls work only with the surrounds.

The center of the front panel is the mode section, which comprisestwo switches: Sidechain Sum and the dual-stereo mode discussed above.Sidechain summation is used when one instrument or element is tooprominent in all of the channels. When one channel has an element thatis too prominent, XLogic's RMS detector works well to triggercompression. With a multichannel signal, however, it's best to sum thechannels to finesse the overly loud element. Summing in the traditionalsense falls prey to phase cancellation (especially in recordings ofacoustic environments), so SSL engineered this aspect appropriately:They rectified the signals prior to summation.

The sidechain-adjust section dominates the right half of the frontpanel, and it's the most important and innovative area. The circularMax display with five bi-color LEDs in a pentagon around a center LEDfor the LFE is remarkably intuitive for indicating which channel isdriving the compressor.

Four sidechain trims control how much of each channel or channelpair contribute to the sidechain. These include left/right, center, LFEand surround. Center and surround may be disconnected from thesidechain input by activating their respective iso switches, but theywill still be controlled by the master level control.

The Link switch allows the LFE to merge with the main channels,incorporating it with the sidechain for the main compressor andswitching the control of the LFE signal path to the main compressor.There's also a 12dB per octave, 120Hz filter switch and a 10dB padswitch to reduce the level of the LFE if the mix has been made to DolbyDigital specifications. It would be nice if the 120Hz filter could beexpanded to include 80 Hz, as current Dolby recommendations for the LFEuse in music mixing call for 80Hz lowpass to accommodate playback inconsumer systems with bass management.

The far-right section has two controls with their respective Inswitches: master level and auto-fade. Master varies from ▸ tounity gain. Auto-fades can range from 1 to 60 seconds. Releasing thelighted auto-fade switch creates a fade-in, while engaging the switchcreates a fade-out.


SSL arranged the XLR inputs and outputs in the standard ITUgrouping: L, R, C, LFE, Ls and Rs — an excellent choice. There'salso a big heat sink, but you'll still need that space above the unitif you place it in a rack. Next to the power switch and IEC cable inputis the housing for a removable vertical PCB that can be configured forsettings of 100V, 120V, 200V and 240V.


Working with the compressor brought back many fond memories ofworking with SSL consoles. I used to call the Quad compressor the“make-it-bigger button,” and I distinctly remember thatcompressor's characteristics.

With XLogic, however, the engineer should tweak very carefully,because it is easy to misuse the box and render a formerly spacious mixinto a cramped space that sounds like a closet. I also found that withcertain channel trim settings, I could put the machine into a statethat caused radical changes on an acoustic guitar (recordedmultichannel) by simply changing threshold from 1.5 to 2, while varyingthe attack throughout its range seemed to do relatively little.Theanswer to these problematic situations lay in the trim control section.The prudent engineer will want to focus immediate attention onexercising variations in trim control relationships.

Of course, a little compression goes a long way. For one session, Irecorded a vocalist/guitarist in surround. Although the vocalist wasclosely miked, his guitar still bled into the vocal microphone. Becausehis vocals were also picked up by ambient microphones, I faced a mixwith a very dominant center-channel vocal, a stereo front that wasmostly guitar and surround channels that were nearly perfect.

I needed to make the vocals “sit” in the mix rather thandominate it. Again, the solution involved tweaking the channel trims. Ilet the center channel contribute most to the sidechain, with a bit ofthe left and right channels also going to the sidechain. I isolated thesurrounds from the sidechain so that they were only affected by themain out and not the compressor. I also summed the sidechain so thatthe main contributor to the compressor was the vocal and not theguitar. Finally, I set the top compressor controls with a fairly slowattack and release and a very gentle ratio of 2:1.

I had to work with the trims quite a bit so that the compressordidn't squash the front ambience. At certain settings, the wall behindthe guitarist seemed to leap forward, but after playing with varioussettings, I was able to make the guitarist sit comfortably in thecenter with his vocals focused but not overbearing. The ambienceremained relatively untouched.

The XLogic Multichannel Compressor is elegant with logical yetcomplex routing, excellent components and, most of all, the classic SSLbus compressor's sonic signature. The unit gives the engineer ultimateflexibility and control over multichannel mixes in the analogdomain.

Solid State Logic, 212/315-1111,

K.K. Proffitt is chief audio engineer of JamSync inNashville.