Lexicon MPX-550
A single Lexichip, 255 programs, and a $649 reverb in a 1U box.
Overview
The MPX-550 is a 1U dual-channel multi-effects processor. The spec sheet covers a lot before anyone plugs it in. The A/D and D/A converters are 24-bit, with 105 dB and 101 dB of dynamic range respectively. Internal processing is 24-bit too. Frequency response is 20 Hz-20 kHz within ±1 dB, and sampling rates are selectable between 44.1 and 48 kHz. It weighs three pounds and is 1U tall with a 4-inch depth, so it's shallow enough to sit in a rack without eating the whole cavity.
What separates the 550 from the rest of the MPX line is that it runs on a single Lexichip, Lexicon's custom reverb processor. Sound On Sound (January 2003, p.40) noted that the MPX-550's features and sound quality put it well above the entry level. The 255 factory programs cover time- and frequency-based effects plus dynamics processing. The unit can be used as an insert, across a stereo mix bus, or between an instrument and an amp.
The I/O is serious for the price. There are two XLR and two ¼-inch TRS analog inputs, the same complement on the outputs, S/PDIF digital I/O on RCA coaxial, MIDI In and Out/Through, and a ¼-inch TRS footswitch jack. The 24-bit converters, per Sound On Sound (January 2003, p.40), deliver more dynamic range than most home studios could hope to do justice to. There are 64 user locations alongside the 255 presets.
The front panel centers on a backlit LCD. It shows the current program, a graphical representation of the DSP building blocks and how they're patched together, and level meters. Four rotary encoders sit to the left of the screen, and each knob's function is labeled at the bottom of the display rather than over the knob itself. A large rotary knob on the other side scrolls through presets and user programs and pushes in to access Banks. Editing can run as deep as five screens, but Sound On Sound (January 2003, p.40) described the interface as easy to navigate and understand.
The first encoder is labeled Adjust, and it's the smartest thing on the panel. It gives instant access to the parameters Lexicon expects you to reach for first on a given program. On hall reverbs, Adjust moves midfrequency reverb time and decay slope together. On plate programs it controls reverb decay and high-frequency rolloff simultaneously. In a delay program it might just be feedback. Most tweaking happens without diving into menus at all.
The compressor lives on the final edit page of every program except the mastering-oriented dynamics programs. Its parameters can be set globally or stored per-program. The dynamics section also includes peak limiting, expansion, and compression, and the expansion and compression programs carry a subtle saturation algorithm in "modern" and "vintage" variations. Sound On Sound (January 2003, p.40) found that saturation increased density at a slight cost in clarity.
Programs are arranged in five categories: Single, where the whole processor is devoted to one effect; Dual, which stacks two effects; Special Effects; Mastering Dynamics; and Live-FOH for front-of-house work. Within each category, programs group into Banks of similar types - plate reverbs, hall reverbs, gated reverbs. The single programs include tremolo, chorus, flange, pitch-shifting, and delay/echo with up to six taps and feedback. There's also a rotating speaker program called Rotary, modeled on the Leslie Model 122, which simulates a woofer and tweeter spinning in opposite directions. Delay programs can be set to a filtered tape-echo simulation that darkens with each repeat, or configured so each of the six delay channels shifts relative to the current tempo. The dual programs pair flange, chorus, or pitch-shifting with reverb or delay in series or dual-stereo configurations. Sound On Sound (January 2003, p.40) judged them completely usable but not quite as rich as the single programs.
MIDI implementation is thorough, as expected from Lexicon. Controller numbers are preassigned to editing parameters and can be reassigned from the front panel. A knob can also learn a controller by being moved, and the distance traveled scales the parameter range. Program changes run over MIDI. The entire user bank, current program, or system setup can be dumped and loaded, and all parameters respond to System Exclusive. Delay times and modulation rates can sync to MIDI Clock, and the unit can derive tempo from a suitable audio source.
The Bypass button does more than most. It can mute the whole unit, mute only the input so you hear just the effects at the output, or pass input straight to output through the 24-bit converters, which turns the MPX-550 into a standalone A/D converter. Dry signal can be routed to the digital outs while the analog outs carry wet, which is handy for live recording splits.
Two caveats before buying. The S/PDIF digital I/O interacts oddly with the Mastering Dynamics programs. Sound On Sound (January 2003, p.40) found the effect reduces input level, requiring gain raised to 7 to match the bypassed signal even with all parameters flat. That's a real annoyance if you're inserting it digitally. And the dual programs, while useful, trade some of the richness of the single-effect algorithms for their flexibility. The Sound On Sound review praised good sound quality, an excellent program selection, quick parameter access, and hassle-free digital I/O, with the mastering-effects level drop as the lone con. The price is $649, and the box sits below Lexicon's flagship processors.
The MPX-550 shares its lineage with the MPX-500 it updates and sits above the entry-level MPX-110. The 550's screen and deeper editability are the dividing line between the two.
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