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Learning the Lexicon

Aug 1, 2001 12:00 PM, By Michael Cooper

Click here to access files referenced in this article

The Lexicon MPX 100 and MPX 500 multi-effects processors are economical alternatives for the budget-conscious engineer in search of Lexicon-quality effects processing. 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. Fortunately, a parameter glossary for the MPX series is available at www.lexicon.com in the support downloads area. Also, though the user interface for both units is mostly straightforward, some controls don't always act the way you expect them to act.

Fortunately, none of those idiosyncrasies diminishes the capabilities of either unit; the boxes just need some explaining. In this article, I'll plumb the inner workings of the two popular processors to reveal undocumented features, offer tips on using some of the lesser-known parameters, and dispel some common misconceptions about operating the units. I'll start with the MPX 100 because it is simpler 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 offers some nice tweaks for spicing up tracks. Here's a look at some of its reverb algorithms.

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

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

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

DELAY GRATIFICATION

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

Fortunately, some variations of the Delay-Reverb dual programs give you front-panel access to the parameter by proxy. The Cascade routing configuration within variations 7 through 10 is your ticket to predelay gratification.

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

You can get dramatic predelayed reverb by setting the MPX 100's Effects Lvl/Bal control to the three o'clock position (still referring to the Delay-Reverb variations 7 through 10). With the control set to three o'clock, the MPX 100 produces instant reverb that's then followed by predelayed reverb (see Fig. 3). Again, the predelay time is set with the Tap Tempo function. Set the Adjust knob to produce a medium decay time, and the resulting effect sounds as though you're in an enormous space. The sound reverberates immediately and then seems to bounce off a hard wall at the back of the space to start the reverberation again. The Delay-Reverb variation is similar in principle to 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, David Gilmour-style guitar solos.

I'M TREMBLING

The MPX 100's Tremolo variations can create excellent stereo-autopan effects. The Adjust knob changes the phase angle (called Sweep in Lexicon parlance) between the left and right output signals for Tremolo variations 4 through 8, thus causing a difference in the perceived width of the stereo image. Though the Adjust knob is continuously variable, it actually switches through four discrete polarity settings instead of smoothly moving through phase angles.

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

The Sweep parameter is also available for Flange variations 15 and 16. The Adjust knob steps through four static settings for those patches as well.

DIFFUSION CONFUSION

The MPX 100's Chorus variations 5 and 6 assign a diffusion function to the Adjust knob. Diffusion uses an allpass digital filter to simulate the effect of a sound bouncing off an acoustic diffuser. That is, it smears the sound so that discrete slapback echoes are more difficult to hear. Each echo is repeated in several iterations that have different amounts of amplitude and phase. As you turn up the Adjust knob in the Chorus variations, the Chorus algorithm's six delayed voices sound increasingly less discrete and the sound becomes more “gauzy.” If you're shooting for a softer-sounding Chorus effect, crank the Adjust knob for those variations.

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

MPX 500

Now I'll switch gears and dive into the MPX 500. A quick stroll through the Edit Pages of the processor confirms exactly how powerful and occasionally confusing the unit's editing capabilities are. Unfortunately, the near absence of documentation for parameters handicaps engineers eager to exploit the user-friendly interface to its fullest. Furthermore, some terminology used for the parameters is inconsistent with that of the MPX 100 and even for program variations within the MPX 500 itself. Thankfully, a few pointers easily clarify the disparities.

Note that the following tips apply to version 1.04 firmware. See the sidebar “What's New with Version 2” for a rundown of the additional functionality the new firmware will bring to the MPX 500.

GLOBAL WARNING

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

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

RATE CHANGE

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

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

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

There's one more cryptic parameter to discuss for the MPX 500 Chorus variations: Spread. Spread is a master delay control that adjusts the difference between the shortest and longest delay times for the chorus algorithm's six voices. Cranking up the Spread value results in a more reverberant sound as delay times increase and the delay taps are spaced farther apart. Keep Spread set to a low value if you're shooting for a tighter, more focused sound.

PLAYING TAPS

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

A value of ±100 percent denotes modulated tap amplitudes equal to that of the fixed taps (“+” being positive polarity and “-” being inverted). Because closely spaced occurrences of a sound and its modulated iteration create the greatest destructive interference when they are at equal amplitudes, you get the deepest comb-filtering effects from the MPX 500 by setting the Adjust knob to ±100 percent Depth. A 0 percent Depth setting results in no flanging but nevertheless provides an excellent stereo effect on strummed acoustic guitar (in mono) and keyboard comp tracks.

HEAVEN'S GATE

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

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

The Spread parameter's setting determines how quickly the reverb's density builds up. Low settings cause the density of reflections to build up quickly, making the reverb behave like a small chamber; high settings cause a slow buildup of density, similar to the effect of a large hall. For a dramatic but controlled inverse gated-snare sound, try dialing in a medium-long Shape setting (perhaps around 145) and a low Spread setting (roughly 88). If you set the Spread too high with a generous Shape value, the sound will generally become too diffuse to maintain a tight groove. Try lowering the Diffusion parameter to about 48 percent for a coarser, more aggressive sound.

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

MUTE OUTPUT

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

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

WHAT'S NEW WITH VERSION 2

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

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

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

The number of factory presets has grown to 255 (from 240), and the User Bank has increased to 64 programs from 30 in version 1.x. Version 2 recognizes MIDI SysEx dumps performed with a version 1-loaded MPX 500.

FEATURES OF THE NEW MPX 200

Like the MPX 500, Lexicon's new MPX 200 multi-effects processor ($399; now shipping) is a true stereo-effects processor that features 24-bit A/D and D/A converters and S/PDIF I/O. Whereas the MPX 500 supports 44.1 and 48 kHz sampling rates, the MPX 200 is strictly a 44.1 kHz box (like the MPX 100).

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

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

Other amenities include unbalanced ¼-inch inputs that can accept line or direct-instrument input; unbalanced ¼-inch TRS outputs that deliver line-level signals or headphone output (left channel only); a software-selectable MIDI Out/Thru port; Cue program mode; bypass; and a built-in power supply.