Learning the Lexicon

Although the MPX 500 and, to a much lesser extent, the MPX 100 let you edit parameters to dial in custom effects, trailblazing beyond presets can be difficult because of an almost complete lack of documentation about those parameters.
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The Lexicon MPX 100 and MPX 500 multi-effects processors areeconomical alternatives for the budget-conscious engineer in search ofLexicon-quality effects processing. Although the MPX 500 and, to a muchlesser extent, the MPX 100 let you edit parameters to dial in customeffects, trailblazing beyond presets can be difficult because of analmost complete lack of documentation about those parameters.Fortunately, a parameter glossary for the MPX series is available at www.lexicon.com inthe support downloads area. Also, though the user interface for bothunits is mostly straightforward, some controls don't always act the wayyou expect them to act.

Fortunately, none of those idiosyncrasies diminishes thecapabilities of either unit; the boxes just need some explaining. Inthis article, I'll plumb the inner workings of the two popularprocessors to reveal undocumented features, offer tips on using some ofthe lesser-known parameters, and dispel some common misconceptionsabout operating the units. I'll start with the MPX 100 because it issimpler to use and offers much that can also be applied to the MPX 500.For a sneak preview of Lexicon's newest offering, see the sidebar“Features of the New MPX 200.”

MPX 100

Though not nearly as programmable as the MPX 500, the MPX 100 offerssome nice tweaks for spicing up tracks. Here's a look at some of itsreverb algorithms.

It's often tempting to lengthen a track's reverb tail to create agreater sense of depth. But all too often, you get a dense wash ofreverb that obliterates detail in the mix and makes everything soundtoo far away and indistinct. The MPX 100's Live Concert (Chambervariation 11), Vocal 1 and Vocal 2 (Chamber variations 15 and 16,respectively), as well as Vocal Plate (Plate variation 8) offer ways togain a sense of depth without turning your masterpiece into pea soup.With those programs, the Tap Tempo function sets the delay time for afeedback loop operating on the input signal. The resulting echo feedsthe Chamber or Plate algorithm, causing the reverb to repeat. Thatadded spice can be just the ticket for giving a lead vocal, leadguitar, or snare drum the depth you want without sacrificingclarity.

For starters, route your track to the MPX 100, call up one of thepreviously mentioned programs, and tap in a quarter-note value with thefront-panel Tap button. You can also use MIDI or the Audio Tap functionto set the tempo. At 100 bpm, you should hear the track's reverb repeatat 600 ms intervals once or twice before it dies off. That gives theeffect of the instrument's sound bouncing off walls two football fieldsaway. Talk about depth!

A quarter-note Tap value shouldn't cause clutter as long as you'reworking with a slow to midtempo song, because the repeats are fixed atsuch a low level (6 percent feedback level for Live Concert and 12percent for the other three variations), so the rhythmic effect theyprovide is subtle. The effect will usually muddle an uptempo tune,however. In fact, the repeating effect can be so elusive that it oftencan't be detected unless the initial impulse of reverb dies out alittle beforehand. First, turn the Adjust knob fully counterclockwiseto decrease the reverb's Liveness to its minimum value; then, slowlyincrease the setting to taste. Liveness is a master control for as manyas four parameters, including midfrequency reverb-decay time. With theLiveness/decay time shortened adequately, the reverb repeats can beheard more clearly because they are not competing with an overlappingwash of initial reverb.


Using front-panel controls, you can tweak the reverb predelay timesfor some of the MPX 100's Gate and Plate variations, but not for theRoom, Hall, and Chamber programs. (You can, however, tweak predelaysettings in the reverb programs by manually entering SysEx messagesinto a sequencer; for complete instructions about that operation, clickon EM Links at the top of this article.)

Fortunately, some variations of the Delay-Reverb dual programs giveyou front-panel access to the parameter by proxy. The Cascade routingconfiguration within variations 7 through 10 is your ticket to predelaygratification.

With Cascade routing, left and right inputs feed two stereo effectsthat are chained together in series (see Fig. 1). ForDelay-Reverb variations 7 through 10, the MPX 100's Effects Lvl/Balknob adjusts the amount of delay and dry signal that will be fed to thereverb. When you set the Effects Lvl/Bal knob to the 12 o'clockposition for any variations, input to the stereo reverb is derivedsolely from the output of the stereo delay (see Fig. 2). Thedelay time, which is set with the Tap Tempo function, becomes thereverb's predelay time. You can add impressive depth to lead vocals andsax solos, yet retain clarity, by adding a short predelay to theirreverbs. As with other delay-based effects, the predelay time shouldtypically be synchronized with the song's tempo.

You can get dramatic predelayed reverb by setting the MPX 100'sEffects Lvl/Bal control to the three o'clock position (still referringto the Delay-Reverb variations 7 through 10). With the control set tothree o'clock, the MPX 100 produces instant reverb that's then followedby predelayed reverb (see Fig. 3). Again, the predelay time isset with the Tap Tempo function. Set the Adjust knob to produce amedium decay time, and the resulting effect sounds as though you're inan enormous space. The sound reverberates immediately and then seems tobounce off a hard wall at the back of the space to start thereverberation again. The Delay-Reverb variation is similar in principleto the MPX 100's Live Concert, Vocal 1 and Vocal 2, and Vocal Plate,but it is far more intense. It's excellent for use on grandiose, DavidGilmour-style guitar solos.


The MPX 100's Tremolo variations can create excellent stereo-autopaneffects. The Adjust knob changes the phase angle (called Sweep inLexicon parlance) between the left and right output signals for Tremolovariations 4 through 8, thus causing a difference in the perceivedwidth of the stereo image. Though the Adjust knob is continuouslyvariable, it actually switches through four discrete polarity settingsinstead of smoothly moving through phase angles.

Here's the scoop: the knob starts at a 0 degree L/R phaserelationship when set to full counterclockwise (CCW). It then moves toa 90-degree angle at about the 9:30 position, a 180-degree angle justpast 12:30, and a 270-degree angle roughly past 3:30. A 0 degreesetting creates a mono effect; the stereo image is widest at 180degrees; and both the 90- and 270-degree settings create a narrowerstereo image (and essentially the same effect). In all cases, the TapTempo function lets you adjust how fast the image bounces from speakerto speaker. It's usually best to synchronize the bounce to the beat ofthe music or, for slow-tempo pieces, to some subdivision thereof.

The Sweep parameter is also available for Flange variations 15 and16. The Adjust knob steps through four static settings for thosepatches as well.


The MPX 100's Chorus variations 5 and 6 assign a diffusion functionto the Adjust knob. Diffusion uses an allpass digital filter tosimulate the effect of a sound bouncing off an acoustic diffuser. Thatis, it smears the sound so that discrete slapback echoes are moredifficult to hear. Each echo is repeated in several iterations thathave different amounts of amplitude and phase. As you turn up theAdjust knob in the Chorus variations, the Chorus algorithm's sixdelayed voices sound increasingly less discrete and the sound becomesmore “gauzy.” If you're shooting for a softer-soundingChorus effect, crank the Adjust knob for those variations.

If you want a modulation effect with extra oomph, check out theChorus or Flange variations that assign the resonance parameter to theAdjust knob. Resonance causes the Chorus or Flange delay lines to feedback on themselves. The Adjust knob is a bipolar control for theprogram variations. Turning the knob clockwise from the 12 o'clockposition introduces positive feedback into the algorithm's delay lines,and turning the knob counterclockwise introduces negative feedback. Asyou turn the Adjust knob farther in either direction, a greater portionof the signal feeds back upon itself. Positive and negative feedbackcause phase cancellations, resulting in notches (comb filtering) in theeffect's frequency response. Because Chorus and Flange modulate theirdelay times, the notches are also modulated. The result is a sweep thatsounds great on instruments, such as organ and electric guitar, thatproduce sustained tones.

MPX 500

Now I'll switch gears and dive into the MPX 500. A quick strollthrough the Edit Pages of the processor confirms exactly how powerfuland occasionally confusing the unit's editing capabilities are.Unfortunately, the near absence of documentation for parametershandicaps engineers eager to exploit the user-friendly interface to itsfullest. Furthermore, some terminology used for the parameters isinconsistent with that of the MPX 100 and even for program variationswithin the MPX 500 itself. Thankfully, a few pointers easily clarifythe disparities.

Note that the following tips apply to version 1.04 firmware. See thesidebar “What's New with Version 2” for a rundown of theadditional functionality the new firmware will bring to the MPX500.


Flange variations 75 and 77 control the Speed parameter using Editknobs 1 (Adjust) and 2 (a soft knob on Edit page 1). Note that theAdjust knob's function is labeled somewhat confusingly Rate. The knobscontrol how fast the delays modulate between their extreme values.However, the knobs' respective scales are arbitrary (that is, without aunit value) and not related, so it would be fruitless to try to find anequivalent point for both scales or to infer millisecond or percentagevalues from their readouts.

Remember that the Adjust knob is essentially a convenient programcontroller that can modify one or more parameters simultaneously. ForFlange variations 75 and 77, it provides a link to the Speed control(Edit knob 2) only (as opposed to programs for which the Adjust knobcontrols several parameters simultaneously), and its range is set towhat Lexicon engineers thought would be optimal for the parameter. Therange for the Speed parameter, set by Edit knob 2, is more extensive.For example, you can set the modulation speed with the Adjust knob tox and increment its value further with Edit knob 2 (Speed) tox+10. However, if you change the Adjust knob again, the Speedparameter's value will instantly increase or decrease from xand not from x+10.


On many digital delay lines (DDLs), the speed or rate parametercontrols how fast the delay time sweeps over the range set by thewidth/depth control; typically, the range varies from approximately 0.1to 10 Hz (that is, as many as ten modulation cycles per second).Changing the width/depth control does not change the frequency withwhich the DDL modulates across the range. Thus, a greater width/depthvalue causes the same speed/rate setting to modulate over a greaterdistance during the same elapsed time, effectively increasing thelinear speed of travel. If the delay time must modulate further at thesame frequency, it must move faster to do so.

The MPX 500 works differently. When you set its Speed parameter fora Flange or Chorus variation, you are fixing the modulation at a moreor less constant speed. The Chorus variations actually modulate inpseudorandom fashion versus the constant,low-frequency-oscillator-based action provided by the Flangevariations. The speed is unaffected by adjustments to the Sweepparameter. The Sweep parameter for the variations is equivalent to aDDL's width/depth parameter; it determines how far the modulating delaytime will stray at its extremes, expressed in milliseconds differencefrom the delay tap's base setting. Therefore, increasing the Sweepvalue results in a slower rate, because the modulation takes longer togo the increased distance at its essentially fixed speed. To keep theMPX 500's cyclical modulation rate roughly the same, you must readjustthe Speed inversely to the Sweep parameter's changing value.

Don't confuse the MPX 500's Sweep parameter with the MPX 100's. The500's Sweep provides control of Flange and Chorus modulation widths;the 100's Sweep adjusts the phase-angle difference between left andright output signals for several Flange and Tremolo variations. For theMPX 500's six-voice Chorus variations, Speed 1 and Sweep 1simultaneously control the left channel's three voices, and Speed 2 andSweep 2 control the right channel's three voices.

There's one more cryptic parameter to discuss for the MPX 500 Chorusvariations: Spread. Spread is a master delay control that adjusts thedifference between the shortest and longest delay times for the chorusalgorithm's six voices. Cranking up the Spread value results in a morereverberant sound as delay times increase and the delay taps are spacedfarther apart. Keep Spread set to a low value if you're shooting for atighter, more focused sound.


The MPX 500's Flange variations provide yet another enigmaticparameter that is important to understand. Most manufacturers use theterm depth (in regard to flanging) to refer to how much thedelay time in the signal's out-of-phase portion modulates away from thebase value. For the MPX 500's Flange variations, however, the Depthparameter determines the relative amplitude of both channels' modulatedtaps with respect to their fixed taps.

A value of ±100 percent denotes modulated tap amplitudes equalto that of the fixed taps (“+” being positive polarity and“-” being inverted). Because closely spaced occurrences ofa sound and its modulated iteration create the greatest destructiveinterference when they are at equal amplitudes, you get the deepestcomb-filtering effects from the MPX 500 by setting the Adjust knob to±100 percent Depth. A 0 percent Depth setting results in noflanging but nevertheless provides an excellent stereo effect onstrummed acoustic guitar (in mono) and keyboard comp tracks.


The MPX 500's editing facilities allow you to create a variety ofgated-reverb sounds. Two key parameters that work hand in hand with theGate variations are Shape and Spread. Neither parameter does muchunless the other is at a healthy level (at least 20 to 30 percent ofits maximum setting).

Shape determines the amplitude profile of the gated reverb (how fastthe amplitude of the reverb's delay taps will rise over time).Low-value Shape settings cause an almost instantaneous buildup much theway a real plate reverb performs during its initial stage ofexcitation. High Shape values, on the other hand, cause an inverseeffect in which the reverb's amplitude rises relatively slowly. Dial ina very high value, and the sound mimics a reverb tail played backwardon a tape recorder. Remember those?

The Spread parameter's setting determines how quickly the reverb'sdensity builds up. Low settings cause the density of reflections tobuild up quickly, making the reverb behave like a small chamber; highsettings cause a slow buildup of density, similar to the effect of alarge hall. For a dramatic but controlled inverse gated-snare sound,try dialing in a medium-long Shape setting (perhaps around 145) and alow Spread setting (roughly 88). If you set the Spread too high with agenerous Shape value, the sound will generally become too diffuse tomaintain a tight groove. Try lowering the Diffusion parameter to about48 percent for a coarser, more aggressive sound.

Also try experimenting with the gate's High Slope and Low Slopeparameters. Positive-value slopes increase the amplitude of thereverb's reflections over time but limit their effect on high or lowfrequencies, depending on which slope parameter you're tweaking.Setting Low Slope to a higher value than High Slope generally givesdrum tracks more weight. Start with a Low Slope setting of +8 and aHigh Slope setting of +3 and tweak to taste.


Hopefully this article will help you improve your effects-editingchops. Tap the inner power of the MPX 100 and 500, and the new soundsyou'll Shape are bound to Sweep you off your feet.

Michael Cooper does not live on a Slope. He is the owner ofMichael Cooper Recording, located in beautiful Sisters, Oregon.


Version 2 software ($119.95; now shipping) for the MPX 500 extendsthe unit's capabilities by adding a dedicated 2-channel compressor, newmetering parameters, improved ambience, and additional RAM memorylocations for storing user presets.

The new compressor is available on all presets and is always placedin front of the effect(s) in the wet portion of the signal path.Dedicated compressor-only presets are also provided. The compressor canfunction as a stereo processor or as a single-channel compressor withthe unused channel serving as a sidechain input. Available compressionratios are 1:1 (off), 2:1, 3:1, 4:1, 5:1, and 10:1. Threshold isadjustable from 0 dBFS (digital saturation) to -32 dBFS. Editedcompressor parameter settings can be applied on a program-by-programbasis or globally with a new System parameter called CompressorMode.

Gain reduction is indicated by a descending bar between the twoinput-level meters and is calibrated in 2 dB increments. Version 2 alsoprovides 0, -6, -18, and -32 dB calibration marks for the input-levelmeters for easier level setting.

The number of factory presets has grown to 255 (from 240), and theUser Bank has increased to 64 programs from 30 in version 1.x. Version2 recognizes MIDI SysEx dumps performed with a version 1-loaded MPX500.


Like the MPX 500, Lexicon's new MPX 200 multi-effects processor($399; now shipping) is a true stereo-effects processor that features24-bit A/D and D/A converters and S/PDIF I/O. Whereas the MPX 500supports 44.1 and 48 kHz sampling rates, the MPX 200 is strictly a 44.1kHz box (like the MPX 100).

Powered by Lexicon's proprietary Lexichip, the 1U rack-mountable MPX200 provides 240 factory presets and 64 user RAM locations. The effectsalgorithms are reminiscent of those found in the MPX 100 and 500; theyinclude Ambience, Plate, Chamber, and Inverse Reverbs as well asTremolo, Rotary, Chorus, Flange, Pitch Shifting, Detune, 5.5-secondDelay, and Echo programs. As with an MPX 500 running version 2software, the MPX 200 provides a digital compressor for its programs sothat you can run two effects and compression simultaneously. As many aseight parameters (four for the compressor) can be edited in eachprogram with front-panel controls.

Other aspects of the MPX 200's feature set should also soundfamiliar to MPX 100 and 500 users for example, Dual Stereo (parallel),Cascade, Mono Split, and Dual Mono routing configurations. MIDI controlincludes Program Change, Bulk Dump, and a Learn mode for assigningfront-panel parameters to MIDI messages. You can lock delay times andmodulation rates to MIDI Clock or a Tap Tempo function. The latter iscontrollable from an audio-input trigger, a front-panel Tap button, adual footswitch, an external MIDI controller, or a MIDI ProgramChange.

Other amenities include unbalanced ¼-inch inputs that canaccept line or direct-instrument input; unbalanced ¼-inch TRSoutputs that deliver line-level signals or headphone output (leftchannel only); a software-selectable MIDI Out/Thru port; Cue programmode; bypass; and a built-in power supply.