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Lexicon MPX100

Dual-channel Effects Processor By Paul White
Published August 1998

Lexicon MPX100

If you've £250 to spare and a reverb‑shaped hole in your studio, Lexicon would like you to fill it with their latest budget processor, which offers 20‑bit converters, a digital output as standard, and the famous Lexicon Ambience effect.

The MPX100 is the first in a range of processors based on Lexicon's new Lexichip III reverb processing engine, an extremely powerful custom device capable of running Lexicon's famous high‑quality reverb algorithms without cutting corners. Lexicon have ventured into the budget effects market before, notably with the Alex and the Reflex, so affordable Lexicon effects are no longer unheard of, but the MPX100 offers a few refinements that could make it attractive to anyone searching for decent‑quality effects on a shoestring. For a start, it differs from its predecessors in that it has 20‑bit input and output converters running at 44.1kHz. Combined with an internal 24‑bit signal path, this gives a dynamic range of over 95dB using the analogue output, but Lexicon have also included an S/PDIF digital output that extends the dynamic range to better than 100dB.

Lexicon's new unit provides reverb, as you'd expect, but also adds a wide selection of non‑reverb effects, from delay and chorus to rotary speaker simulation and pitch shift. The control system hints at the well‑worn Alesis Microverb/Midiverb arrangement, where the user simply picks one of 16 variations on one of 16 preset effects themes, but there's actually rather more to it than that.

Hardware Overview

Physically, the MPX100 is a 1U‑high, 2‑in, 2‑out effects processor based on 240 presets that can be edited on a fairly basic, but nevertheless useful level. The analogue I/O is on unbalanced jacks, with a high‑impedance input that will accept electric guitars as well as regular line sources. For practice purposes, the left output jack doubles as a phones output, though it's not very powerful.

The colour scheme is traditional Lexicon and the stylish knobs have a very up‑market feel to them. There's no display window, though, and only dual red/green LED indicators to monitor the input level. For the benefit of live players, there's a rear‑panel Tap and Bypass footswitch socket. Power comes from an external adaptor.

Lexicon MPX100 rear connections.Lexicon MPX100 rear connections.

A surprising amount of MIDI functionality is built into the MPX100, not least the ability to synchronise certain delay and modulation parameters to MIDI Clock. It's also possible to access all the patches via MIDI, using Bank Change and Program Change messages. Naturally, there are two MIDI sockets for MIDI In and MIDI Out/Thru.

Conventional rotary controls are used for setting input level, wet/dry mix and output level, and all but the input level setting can be stored, along with the Tap time, as part of a user patch. Tap is used to set the delay time of certain echo‑type effects or the pre‑delay time of some reverb patches. It's also used in various presets to set modulation rates.Even the Adjust knob isn't as straightforward as it seems — in some modes it operates as a conventional 'amount' knob, in others it operates either way from the centre position, and sometimes it behaves as a switch. It also alters more than one parameter on some patches, a trick it doubtless learned from the PCM80 and PCM90! There's a Store button for saving edited patches back into one of just 16 user memories, and holding this down at the same time as Tap puts the box into MIDI learn mode, so that an external MIDI controller can be used to modulate a key effect parameter.


Both single and dual effects are featured on the MPX100. All the single effects are available on the left‑hand side of the rotary Program Selector switch, with the 16 variations of each selected via the Variation knob. As you'd expect, the usual reverbs, choruses, flangers and delays are there, but — for the first time on a budget Lexicon unit — you also get their classic Ambience algorithm, which is great for making a dry sound 'belong' in a mix without adding obvious reverb. On top of that, there's a selection of tremolo effects plus a rotary speaker simulation where the two virtual rotors spin independently and in opposite directions. The braking and acceleration rate of the real thing is also carefully modelled. A surprisingly sophisticated pitch‑shifter is also included.

In the delay section, long delays of up to 5.7 seconds are possible, and the delays all have a choice of clean or tape‑style operation, the latter producing more diffuse and warmer‑sounding repeats. These are both available within each preset by turning the Adjust knob clockwise from centre for tape echo and anti‑clockwise from centre for regular, clean DDL effects. Many of the modulation effects feature up to six voices (a spin‑off from the PCM80), so you can create very rich chorus effects.

The dual effects patches combine various modulation effects with either delay or reverb, and there's also a 'delay plus reverb' configuration. It's in this mode that the Adjust knob operation sometimes gets a bit clever, because it adjusts the contribution of the two effects within the current routing setup by controlling how much of the dry signal and how much of the first effect is fed into the second effect (at extreme settings, the result is one effect or the other). Unless you have a trainspotter memory you'll need the manual while editing, as the routing is different depending on which variation you choose.

The same system is carried through all the dual effects, such that the first six variations sum both inputs to both effects blocks, which are arranged in parallel. The two sets of stereo outputs are then mixed. The next four variations are based on two stereo‑in, stereo‑out effect blocks in series, while the following three are true dual effects, arranged so that the left input feeds one effect and the right input the other. Again, the stereo outputs are summed to provide a composite stereo signal. Finally, there are three further variations where each input feeds its own mono‑in, mono‑out effects block. Most of these combinations have editable parameters controlled by both the Adjust knob and the Tap button.

One bank falls into neither the dual or single categories, as it produces special treatments that draw on elements from other effects. Here you'll find an infinite reverb (actually, it's stopped now, but it's good for a minute or so!), a weird combination of pitch‑bend and delay called The Abyss, ducking reverbs and delays, spiralling pitch shifts, infinite repeats and panning delays.

In Use

Operating the MPX100 is extremely simple, but without the manual you might be a little lost as to what the Adjust knob, or even the Tap button, is controlling. The overall sound quality is much better than you'd expect from a budget unit and the input is reasonably tolerant of small overloads. Patches with lots of feedback, such as flanging, tend to be just a little noisy, and the large amounts of feedback make them vulnerable to overload, so you have to be rather careful with the levels. This is true of all effects units, but an analogue input limiter, such as the one on Lexicon's own MPX1, might have made setting up easier.

For the first time on a budget Lexicon unit you get the classic Ambience algorithm, which is great for making a dry sound 'belong' in a mix without adding obvious reverb.

As for the sound of the new unit, the reverbs have the classic Lexicon character that allows you to use very high levels of effect without drowning the dry signal. In terms of quality, they're a lot closer to the MPX1 and PCM80 than they are to the old Reflex and Alex, and all have a good sense of 'realness'. In most cases, the Adjust knob sets the decay time or tonality of the reverb and Tap, where applicable, varies either pre‑delay or an echo delay. Some patches also have pre‑delay mapped to tempo, so that when MIDI Clock is running you get a 32nd‑note pre‑delay.

The reverb algorithms on some reverb units can sound rather 'samey' from one to the next, but with Lexicon each algorithm is distinctive. They're very three‑dimensional effects — even the smaller rooms, which have exactly the right character and coloration. What's more, most of the algorithms are suited to music production, so as well as typical concert halls and churches, you get bright rooms suitable for drums or guitar, intimate live rooms, vocal rooms, and so on. Especially interesting is Ambience, an algorithm first used on the big, expensive Lexicon 300s and 480s, and later on the PCM90 and MPX1. This emulates the reflections and colorations imposed by a real space, so it's good for placing dry‑miked sounds in a real space without having to add reverb. The smallest ambience is designed for voice‑over work, and the treated sound seems almost deader than the dry sound, if that's possible. At the top of the ambience scale is Marble Foyer, where the early reflections are quite obvious, but still die away quickly. Here the Adjust knob controls 'liveness', making this a useful preset for drums and acoustic guitar.

In the tremolo section are several different modulating waveform shapes, ranging from a choppy square wave to a rectified sine wave reminiscent of old guitar amps. Stereo pans are included, with various phase relationships between the left and right channels, as well as a handful of rotary speaker effects. The latter are musically pleasing and have the right speed dynamics, but they still don't seem quite real.

The ability to specify multiple voices on the MPX100 produces a nice rich chorus effect, but in most cases I prefer the more subtle detuning available from the Pitch effect repertoire. For more radical pitch effects, the shift can be set from ‑2 to +1 octave, and although the processing delay is a little irritating sometimes, the effect itself is a lot smoother than on most of its competitors. All the dual effects worked smoothly for me, with the MPX100 making no apparent compromise on effect quality as a result of generating two effects at once.


It's very easy when reviewing a product like this to forget the price and start listing compromises, but at the asking price of £250 there's nothing I can't forgive the MPX100. OK, it is a little annoying to have to pick up the manual when programming, there are only 16 user memories, you can't name your patches, and there are not many editable parameters, but the vast number of presets means it's easy to get close to what you want very quickly, and the reverbs — which is what you generally buy a Lexicon for — sound way better than they've any right to do for a box of this price. In fact, I'd go so far as to say that most people wouldn't be able to tell whether they were listening to an MPX100 or the rather more expensive MPX1 in a mix. Having 20‑bit converters and a digital output also helps ensure the MPX100 will remain compatible with your future setups, though the lack of balanced I/O may upset a few professionals.

As a main reverb processor, the MPX100 will more than satisfy most project studio requirements, in terms of both versatility and quality, and the fact that it offers other impressive effects too makes it a useful all‑rounder. Those who've already got a decent main processor will still find the MPX100 a good second unit, and anyone without a Lexicon may be surprised by just how well those Lexicon reverbs sit in the mix. Frankly, I think other budget effects in this price range may find the going pretty tough from now on!

MPX100 Programs

Effect Type

Plate Reverb

Gated Reverb

Hall Reverb

Chamber Reverb


Room Reverb















Special FX

Number of Programs






















It's About Timing

Lexicon have made it very easy to synchronise delay and modulation parameters — an important issue, as even the best sounding delay is useless if it's running at the wrong speed for the track. On patches where the Tap function is available, a LED next to the Tap button illuminates, and if it's a delay preset, tapping the button twice will set a delay time equal to the spacing between taps. Of course, you can't get a longer delay than the maximum available in the preset you're editing.

If you're hooked up to a MIDI sequencer and want to change the tempo mid‑song, you can assign a MIDI Program Change to the Tap button (you can also assign another to Bypass). A simple Auto Learn function means that once the MPX100 is primed, the next received Program Change is adopted as the controlling one. A similar Learn system is used to select a continuous controller to access the Mix, Effects, Level/Bal or Adjust knob functions. The exact parameter set by Tap varies from preset to preset, so you will need to keep the manual handy — sometimes it's a delay time, sometimes it's a reverb pre‑delay, and sometimes it's a modulation rate. Another neat operational refinement entails holding down the Tap button to allow two audio input events to set the time. — for example, two drum beats or guitar plucks.

Sync is also possible over MIDI, and the MPX100 recognises MIDI Clocks in the range 40‑400bpm. Whether or not the MPX100 syncs to incoming clock can be set up in the System mode, along with the MIDI receive channel and bypass mode. For bypass, there's a choice of either muting both the dry sound and the effect feed or leaving the dry sound active in bypass.


  • Good range of reverbs, including Ambience.
  • Useful delay and mod effects, especially 'Tape Delay'.
  • Easy to use.
  • Affordable.
  • 20‑bit converters with S/PDIF output always active.
  • Excellent (and brief) manual.


  • Another external PSU!
  • Unbalanced connections only.
  • Lack of editable parameters starts to show when you're editing some of the modulation effects.


The MPX100 gets very close to a big Lexicon sound for very little money.


£249 including VAT.