Descending Moses‑like from the Mount, Lexicon's new dedicated reverb processor brings intelligence from the company's top‑end reverbs. Paul White gets a debriefing...
Lexicon's sleek, 1U‑sized PCM90 looks on the surface to be very similar to the PCM80 introduced a couple of years back (and reviewed in SOS December '94), but appearances can be deceptive. It has virtually the same operating system as the PCM80, the same front panel control layout and pretty much the same block diagram, complete with digital I/O — but there are major hardware and algorithmic differences.
For a start, the PCM90 is more of a reverb processor than a multi‑effects unit, and while the PCM80 uses one Lexicon Lex II chip supplemented by a Motorola 56000 DSP, the PCM90 uses dual Lex II chips, making it much more powerful as a dedicated reverb processor.
While some of the PCM‑style reverb algorithms have been retained, the PCM90 also includes algorithms brought in from the high‑end Lexicon 480L and 300L, perhaps the most notable being the 300L's Ambience algorithm. The dual Lex chips also allow the PCM90 to function in a true split mode, and one very flexible split algorithm taken from the 480L is included, enabling two different mono‑in, stereo‑out reverbs to be set up at once. Plans are in place for an expansion card offering further split reverb functions which utilise one Lex II chip per algorithm, and this is expected later in the year. There are five stereo reverb algorithms in total, and though the PCM90 isn't a multi‑effects unit, there are additional parameters in some of the algorithms that take the effects further than basic reverb, by incorporating delay, modulation and EQ.
Like the PCM80, the PCM90 comes with a library of presets, and these cover all the usual acoustic spaces and plates, plus a few oddball effects. The presets are arranged as five banks of 50 patches, grouped into Halls, Rooms, Plates, Post and Split, with one bank per section. A new addition to the operating system is Keyword sorting, which allows you to tag your favourite patches so that they can be reviewed, database‑fashion. Each preset comes with up to four Keyword tags, but you can change these in Edit mode if they don't meet your needs. In theory, if you want to pick a Drums/Percussion reverb, you can do a Keyword search to view only the patches you've tagged with Drums/Percussion.
One of the really friendly features of the PCM80 was its dual‑complexity user interface, which Lexicon describe as Go and Pro. In Go mode, you get to access a limited range of parameters — only the ones likely to make the greatest difference to a patch. In Pro mode, you can go deeper, to adjust all the available algorithm parameters, or even create custom controls. The custom controls aspect is a useful one, and each patch in the PCM90 can have one or more of its most important parameters assigned to the front panel Adjust knob, which enables you to change, for example, the reverb decay time without having to enter Edit mode at all. Up to four additional custom controls can be created for each effect.
Comparing a high‑end Lexicon to a cheap reverb is like comparing a 3D movie to real life.
A full MIDI implementation is included for remote program selection, plus real‑time control and a powerful set of tempo controls. This means that the rate of tempo‑related effects can be tapped in from the front panel, effect tempo can be locked to an external MIDI device, and there's even the option to generate MIDI clock from the tempo you've tapped in. Tempo may be used to control LFO rates, delay parameters and so on, and there's provision to select different rhythmic tempo divisions for the various parameters in a patch. For example, the LFO might be set to run at twice or four times the delay rate. If a patch is designed to work with Tap Tempo, simply hitting the Tap button twice locks in a new tempo.
The editing parameters are arranged as a matrix for easy access via the front panel plasma display, and the system includes comprehensive modulation facilities which have some parallels with the approach taken by some modular synths. For example, sources including LFOs, envelopes, switches, envelope followers and sample and hold can be assigned to various effect parameters, allowing the effect to either change with time or be in some way modified by the input signal itself. Up to ten modulation patches can be set up per effect, and you can control multiple destinations from a single source, or have several sources acting on the same destination parameter at the same time.
The Hardware
The surprisingly deep 1U case provides a very simple set of front panel controls, a two‑line, 20‑character plasma display, and a back panel full of I/O connectors. Level switching is provided for 0dBu balanced or ‑20dBu unbalanced operation. The input connectors are hybrid XLR/jack sockets that can accept either type of connector. The outputs are available on both jack and XLR, with further phono connectors to provide the S/PDIF digital inputs and outputs. You could write a small book on all the digital input and output options, as these include the ability to add various levels of SCMS, to include pre‑emphasis or not, and to sync to internal or external clock at either 44.1kHz or 48kHz sampling rates. Various error messages help locate potential interfacing problems.
The full complement of MIDI In, Out and Thru sockets is present, and the mains feeds into the unit via a standard IEC mains lead. MIDI mapping facilities are included, along with comprehensive patch‑chaining options and very thorough parameter dumping and reloading options via SysEx. Front panel changes are also transmitted in real time via MIDI.
A card slot allows the internal, 100‑patch user memory to be expanded to 1000 patches using 1Mb PCMCIA cards, and remote control is available using an optional conventional dual footswitch and volume pedal, the latter providing dynamic parameter control. A single memory card may also be used to store up to five complete PCM90 setups.
The internal memory is segregated into five banks of non‑volatile factory presets, plus two user banks which Lexicon calls Registers. Each bank comprises 50 locations, so users without memory cards can store up to 100 of their own patches. The Control button gets you into the system parameters section, where things like MIDI and memory card formatting are dealt with, while Edit lets you access and change the parameters of whatever effect is currently loaded, and Tempo is used to access and set tempo‑related effects. In any editing mode, the parameters are arranged in a matrix of up to 10 columns and 10 rows. The matrix is navigated using the Select knob and the Up/Down buttons, and each parameter name is displayed as you access it. As a rule, the things you are likely to want to adjust most often are located near the top of the stack, with the more obscure stuff on the bottom layers. Navigating through the parameter list is very easy, with good consistency of layout from one algorithm to another.
Patch 'N' Go
Earlier, I mentioned the Go and Pro edit modes. Go mode includes a row of 'soft' matrix parameters that can be changed to provide you with your own custom set of easy access parameters. Essentially, these are simply parameters chosen from the full parameter list that are deemed to be most useful. Like the PCM80, the '90 powers up in Go mode, so that some of the parameters are hidden from you. Switching from Go to Pro (in‑depth) mode is accomplished from the Control mode menu, in which case the full parameter list becomes available. Another feature retained from the PCM80 is the on‑line help system. Most operations are organised so that the switch functions occur when you release a switch rather than when you press it, so if you press and hold a switch for any length of time, a helpful prompt message will pop up. Once the message has appeared, the switch will not perform any action upon its release, so if you decide you had the right switch all along, you'll need to go back and hit it again.
Patches are selected using the Select knob and then loaded into memory using the Load button; they may also be called up via MIDI. Because the reverb algorithms are so complex compared with those found in most other units, the loading time is a little over one second, which can seem quite a long time when you're waiting for it. Though I fully understand why this happens, from an operational point of view it makes it difficult, or sometimes even impossible, to change patch cleanly, in mid‑song. The bypass function can be configured to operate in a number of ways, so you can mute either the input to the effect or the effect output, and a compare function is provided so that edited patches can be compared with the original version.
Some of the PCM90 features come straight from the world of computers, and one such is its capacity to remember the last ten effects you loaded, so that you can go back and see the history of what you did, even if you've forgotten the patch you used. The Keyword search is also similar to a computer database search, and a list of 50 keywords is provided, where up to four can be attached to each patch. As shipped, the unit searches alphabetically, so that all the effects are visible. In Control mode, you can pick a different keyword for sorting.
In Use
Though the PCM90 is very approachable, it has so many hidden depths and possibilities (not least when it comes to MIDI and digital interfacing), that there's a very real danger of spending the whole review getting bogged down in the fine detail, whereas most of you are probably more interested in the effects algorithms and what they actually sound like. As touched upon elsewhere (see the 'Algorithmics' box), the PCM90 creates its effects from five different algorithms, which the manual describes as Random Hall, Ambience, Rich Plate, Concert Hall and Chamber/Room.
The beauty of the system is that you don't have to get involved with anything deep and mysterious unless you want to.
From what I can see, any delay elements in the algorithms tend to be true stereo, in so far as the left and right inputs are processed independently, but I'm assuming that most of the traditional reverb effects are created by feeding both channels into the reverb processor, and then using this to generate a set of left and right reflections based on the mono sum of the left and right input. This corresponds to what happens in most real‑life acoustic environments, though as we shall see later, there are opportunities for split reverb patches using the Chamber/Room algorithm.
From the subjective viewpoint, I don't see how anyone can be disappointed in the PCM90, because it is a thoroughbred Lexicon reverb from top to bottom. I always remember the clean, detailed sound of Lexicon reverbs, but when you put the PCM90 side by side with the competition, you also realise how immensely warm and well‑integrated Lexicon sounds are. From a purely personal viewpoint, I would have found this machine flexible enough if they'd just provided 256 presets with decay and pre‑delay controls, (a kind of high‑end Alex), but as it is, you can either edit in incredible detail or stick to a broad brushstrokes approach. Unless you're working on sounds that are going to be heard in isolation, broad‑strokes editing (such as that offered by Go mode) may be all you ever need. The modulation facilities are less important to my mind than they are on the PCM80, where they can really add movement and interest to complex multi‑effects, but again, there are bound to be some users with the time and enthusiasm to make serious use of them. The beauty of the system is that you don't have to get involved with anything deep and mysterious unless you want to.
Summary
Once again, I've got to the end of a Lexicon review with the feeling that I've only just scratched the surface of what is a hugely flexible reverb processor rivalled only by Lexicon's 'car‑priced' high end units. Some may see £2,600 as being on the expensive side for a box that only does reverb, but Lexicon still do reverb like nobody else, and the PCM90 is as near to perfection as you'll get at this kind of price. Sure, you can buy cheap Lexicons like the Alex and Reflex, and great value they are too, but there really is little comparison between what they sound like and what the PCM90 sounds like. The emulations of real spaces are thoroughly convincing, and yet you still have the ability to construct abnormal or gimmicky‑sounding spaces, which is useful both in music and film/video post‑pro work. Lexicon's reverb seems to become a part of the original sound — it doesn't sound 'stuck on' as some reverbs do — and you seem to be able to add a lot of reverb before losing clarity or intelligibility. There's also a lot less graininess than you get from cheaper units, which suggests a much higher reflection density.
Comparing a high‑end Lexicon to a cheap reverb is like comparing a 3D movie to real life: the movie might be initially impressive, but it's a real relief when you take off those irritating glasses. Reverb is the most important effect in the studio, and it pays to buy the best you can afford. It's probably also relevant that clients in paying studios are invariably impressed by the Lexicon name on the equipment list. I'd weld this unit into my rack if I thought there was the slightest chance the guys at Stirling wouldn't come around armed with an angle grinder (or worse still, an invoice), so in the time‑honoured tradition of all the great tragedies of literature, I'm just going to have to love it and leave it.
Algorithmics: The Lexicon Sound
The key to the Lexicon sound is to be found in the algorithms they use, and the powerful hardware needed to run them. Lexicon's algorithms are unique, and the exact details are a closely guarded secret.
Random Hall is designed to emulate a real building, and combines both reverb and delay. Room Size, Spread and Shape can be tweaked to modify the room character, by varying the envelope with which the reverb builds up and then decays. The procedure is to choose a room size first, and then adjust the other parameters to suit. At higher Shape settings, the reverb takes on a dual decay characteristic, and during discussions with Lexicon's Dr David Gressinger a few years ago, he revealed that this was one of the key elements in making a hall reverb appear natural.
This algorithm incorporates Lexicon's Spin function, which modulates certain reverb parameters to prevent modal resonances predominating at certain frequencies during long decay times. Very high settings can cause a chorus‑like modulation, so this feature should be used sparingly unless you're aiming to create an unnatural effect. The algorithm includes a stereo width option that can be controlled dynamically to create surround effects, though there are warnings about mono incompatibility if this feature is used to excess.
The Ambience algorithm comes straight from the 300L and has the uncanny ability to add supporting reverb without obscuring the original sound. If you want a sound to remain focused but take on a sense of space, this is the one to go for. Again, delays are included for both the left and right channels.
Rich Plate combines delay (with feedback), and a reverb algorithm based on the sound of classic studio plates. The sound is very smooth, very dense and has a bright coloration which works well on vocals, drums and hard brass sounds. As with all five algorithms, pre‑delay is included, as is control over the reverb diffusion.
Concert Hall, as the name suggests, is designed to emulate real buildings used for musical performance, and the reverb is designed to sit behind the original sound rather than loom out at the listener. The reverb build‑up is relatively gradual, and the included post‑reverb compression may be used to shape the reverb decay. A feature of this algorithm is a spatial equaliser which comes right at the end of the signal chain, but before the output width control. This has the effect of controlling the stereo width at low frequencies.
Finally, there's the Chamber/Room algorithm which provides true split reverb performance, where the left‑hand input is processed via one Lex II chip, and the right‑hand channel by the other. Stereo delay is available on both channels, as is pre‑delay, echo feedback and an output high‑cut filter. The reverb itself is designed to be unobtrusive, allowing it to be used in a number of general‑purpose applications, and it is also capable of emulating small, coloured rooms. An Infinite parameter allows the reverb decay to be frozen, and the outputs from both reverbs are mixed together in stereo before appearing at the output.
In‑depth editing of any of the above algorithms involves dozens of parameters, but the matrix system puts the most likely candidates for adjustment near the top of the list. Further modification to the effect can be made by bringing the modulation matrix into play, or by using external real‑time control from MIDI, or the connected volume pedal.
Pros
- Top‑end Lexicon reverb sound.
- Hugely flexible programming options.
- Friendly operating system.
Cons
- Patch‑changing is quite slow.
Summary
Though not as flexible as the PCM80 multi‑effects, the PCM90 provides more sophisticated reverbs that owe a lot to the 300L and 480L models. This is probably the most affordable way yet to get the true high‑end Lexicon reverb sound.