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Lexicon PCM70

Launched over two years ago, the PCM70 digital effects processor is still at the forefront of technology thanks to Lexicon's foresight in making it software updatable and MIDI controllable in every conceivable way. Mark Badger checks it out.

Launched over two years ago, the PCM70 digital effects processor is still at the forefront of technology thanks to Lexicon's foresight in making it software updatable. Mark Badger checks it out.

The Lexicon PCM70 is not 'just' a digital reverb and effects generator of singular quality, it is also a creative MIDI device which goes right to the heart of a problem which I feel is mostly overlooked in our efforts to express ourselves artistically with sound and MIDI. In short, I believe there is a tendency for some people to assume that MIDI-based music has a limited range of expression purely because it is based on a digital system which only has 128 steps of resolution in any direction. I would assert that the only limitations, in terms of one's capacity to express oneself musically, are your own. The PCM70 is a product which makes nonsense of the perceived limitations of MIDI, turning the tables entirely and putting the creative ball right back in our court.

Pause to consider the impact of assigning effects parameters to remote MIDI control, with these messages dynamically controlling one of the finest effects machines you are likely to have the pleasure of listening to. The Lexicon pedigree is one of high quality, high cost, effect and the PCM70 represents their fourth generation of digital processors. Even at £1785 plus VAT it is at the 'budget' end of the family, the cost of the top-of-the-line model 224 being well in excess of £10,000. The fact that so many professional studios have found the 224 essential for their work gives you an indication as to the lengths people are prepared to go for the Lexicon sound. And the PCM70, you'll be pleased to hear, uses the same algorithms that were developed for its upmarket sibling.

In addition to reverberation, many other sorts of sound effect are provided. There are eight basic program types available: five different reverbs, chorus and echo, multiband delays, and what Lexicon label 'Resonant Chord' types. This sounds pretty straightforward until you discover that the factory preset 'memory matrix' contains 42 variations of these basic algorithms.

There are actually two such 'matrices', one devoted to presets (7x10 locations, called Programs) and the other to user storage (5x10 locations, called Registers). The rows of Programs are arranged by type, with the columns representing variations on the theme. There are many more memory locations than there are existing presets and I presume this will enable Lexicon to continue to develop further effects. In fact the review machine contained a recently released software update (version 3.01) which adds the Inverse Room effects to the list of basic reverb algorithms, a perfect example of one of the benefits of software-based machines.

If you have ever edited a synthesizer, you will recognise the type of 'human interface' employed on the PCM70 to overcome the lack of panel space for controls, etc. Once you've loaded a Program or Register, you can access the parameter matrix which controls the program. The 16-character fluorescent display changes to show the parameter whose value you can adjust by turning the data entry knob on the fascia. Lexicon have done their best to make the programming as easy as possible, with the same 'row as type', 'column as variation' organisation found in the Program and Register matrices. There are even 'reminder' features for the program and parameter types you are adjusting. However, it would be a mistake to call the PCM70 'user-friendly'. As with most modern synthesizers, there are simply too many parameters.

It is somewhat surprising then, given the complexity and depth of the unit, how easy it is to use on a basic level. Perhaps the quality of the presets is the key to this ease, and the way in which they have been programmed, reflecting Lexicon's many years of experience with effects processors.

Instead of attempting to describe the presets in detail, I'm going to concentrate on the parameters which create them. Partly because these can be assigned, via MIDI, to your dynamic control in performance, and partly because, like on a synth, it is these which you'll adjust in order to create your own effects. In general there are about 40 parameters for each program type. Let's start by examining those which are present in all programs, regardless of type.


- Balance between effected (wet) and clean (dry) signal appearing at the outputs
- Level of the effected signal
- Program name (up to 13 characters)
- Assignment of the 'soft knob' on the front panel to operate on specified parameters when the machine is not in editing mode
- 10 MIDI patches

The 'soft knob' (no jokes please!) assignment is linked to a feature of the MIDI patch assignments. These let you assign up to 10 other Reverb, Delay, Chorus+Echo, or Resonant Chord program parameters to be controlled dynamically by different incoming MIDI messages. These can be any of the following:

- 32 Continuous Controllers (0-31, including Modulation Wheel, Breath Control, Data Entry, Volume etc);
- 32 Switches (64-95, including Portamento and Sustain);
- Pitch Bender and Aftertouch messages;
- Velocity and the Scale position of the last received Note-On message;
- MIDI Clock.

For those of you without a MIDI system (!), Lexicon include a 'soft knob' assignment in this already extensive list of options, meaning that you can manually adjust up to 10 parameters at once with just the turn of a single dial - useful for stage use. Any assignment can be scaled positively or negatively, with a slope range of 0-128.

Having looked briefly at the parameters you'll find in any PCM70 program, and what sort of MIDI information you can use to control them, we can now investigate what makes the program types different.


The PCM70 gives you control over the room size, low and mid-range reverb times, crossover frequency, high frequency filter cut-off, pre-delay, diffusion, attack, density, low and mid-range reverb stop times (the release time of the reverb sustain, in synth terms), up to three pairs of stereo reflection levels and delay times, and master controls which operate on the delay and level of all reflections simultaneously.

In addition, chorus is available in the 'Concert Hall' programs, the 'Inverse Room' types include extra parameters to control low and mid-range reverb slope and overall duration, and the 'Infinite Chambers' treatments have a single reverb time control.

It would take many pages of text to adequately describe the 22 variations of these reverb algorithms. Subtle, smooth, riveting, awesome, unsettling, evocative, mountainous, miniscule - let's just say that they attest to Lexicon's experience with professional quality reverberation. Some programs are so subtle that you cannot distinguish their presence, others so powerful that the massive spaces burst through your speaker cones with tidal force.

Not content to blow you away with sheer quality of effect, most of the programs are MIDI responsive. 'Infinite AT', for instance, reacts to aftertouch messages by reducing an infinite reverberation time to 29 seconds. This causes the PCM70 to 'hold' the sound appearing at its input. Any modulation information then progressively reduces the reverb time to 2.4 seconds. This combination enables you to capture sounds by exerting pressure on your controlling MIDI keyboard, and banish them with your modulation wheel. This dramatic effect really shows off the quality of the unit; the held sound retains its harmonic content with a complex, syncopated beating rather than breaking up into white noise, and it leaves eight MIDI patch parameters for your own experimentation.

I got very encouraging results by assigning the Lexicon's Mix level to the last incoming MIDI velocity message, causing only low velocity (quiet) messages to accompany 100% effect, higher velocity messages causing the PCM70 output to become progressively 'drier'. With an average of thirty reverb parameters available in each preset for dynamic MIDI control, you would be very hard put to exhaust the creative possibilities.


These offer controls for six separate 'voices': level, delay time (up to 936 milliseconds), high and low filter frequencies, pan position, and 'master' controls which operate on all these parameters simultaneously. Other parameters include diffusion, and feedback level for voices 1 and 2. Some algorithm variations use delays calculated in beats per minute rather than milliseconds, and are programmed to respond to MIDI clock messages in order to produce synchronised tempo-related effects. Very ingenious!

The presets offer seven versions of this effect type, from fluttering echoes which flit across the stereo field, as in 'Six Across', to difficult to describe 'widening' effects as in 'MIDI Mod Pan'. The latter assigns incoming MIDI modulation messages to pan voice 1 from left to right, voice 2 from right to left, and MIDI clock messages to control the beats per minute (BPM). Once again, you are left with several MIDI assignments for your own applications.


Controls are supplied for six separate voices: level, delay (here reduced to a 432 millisecond maximum), pan position, feedback level, and master controls. Other parameters set the chorus on as many voices as you need (1-6 and with a choice of triangular or sinusoidal LFO wave), overall chorus level, diffusion, and high frequency filter cut-off.

There are 10 presets devoted to variations of the Chorus+Echo algorithm. They produce a surprisingly wide selection of traditional effects, from flanging and tremolo to the sort of 'non-linear' effects one might normally associate with reverb-type programs. The two flanging presets, 'Power Phlange' and 'Flange O Echo' are worthy of particular mention. The first is simply brilliant and the second produces sweet little echoes until the PCM70 receives some modulation information, whereupon the sound swings to the right side of the stereo field with a heavy duty flange and then to the left, a very unnerving event!


Again, controls are available for six separate voices: level, pitch, resonance, pre-delay, pan position, and master controls. Further parameters include feedback level control for voices 3 and 6, along with high frequency cut of independent left and right channel filters.

It is these programs which represent the most unique of the PCM70s presets. Though the parameters seem to control distinctly recognisable effects individually, in combination they present the user with sound effects which I have heard on no other device, and which stretch my descriptive powers to their limits. As there are just three variations of this program type included in the presets. I'll make an exception and attempt to describe them in some detail.

MAJOR MOD: This creates stereo major scales which race across the pan field from any input. They arpeggiate as they go and there is something else happening at each speaker which I can only describe as the 'bloom' of tonality. If you put a drum pattern through this preset, and you monitor the fully 'wet' output, you will hear a Spanish guitar accompaniment - honest! Under the same conditions, a 'guitar' patch from an FM synth becomes transformed into a maniacal mandolin being accompanied by Dolphy-style flute playing. Not all sounds produce these stringy results, but any sound can invoke the chordal accompaniment, with even the clicks from my fridge providing an interesting tonal effect.

On this program, MIDI modulation information is set to control the pre-delay master, the last note played controls the pitch master, and pitch bend information controls the pitches of voices 2 and 3 positively, and voice 5 negatively. These parameters result in a fully bent pitch wheel shifting your accompaniment up a musical fourth, full modulation acting as a 'damper' (much like the slap of the flamenco guitarist), and higher notes producing increasingly ethereal results.

MAJOR MODAL: This preset again creates tones from any input sound, but this time the effect goes on for longer and is far more rhythmical. The initial tone is accompanied by a bouncing stereo arpeggiation, then, in rhythm, another tone is produced sounding below the initial one, and on the other side of the stereo field. The only MIDI patch in this preset assigns the last note you input to the pitch master. My 'test' drum pattern produced a clearer result with this program, sounding very much like a closely miked acoustic guitar being played gently, but to an insane 5/3 rhythm which exquisitely enhanced a pretty dull 4/4 kick and snare pattern. Interestingly, the beauty of this accompaniment was very 'start-time dependent' - as long as I played the drum pattern 'from the top' everything was lovely; if I simply pressed the drum machine's 'Continue' button the beauty fractured, with unpredictable results.

AUTO SUSPENSE: To hear this effect properly, the PCM70 really needs to be connected to a device that can produce MIDI clock data (eg. sequencer or drum machine). With no clock input, playing a sound through this preset merely produces a gently throbbing echo of weird digital noise. However, as MIDI clock data is assigned to control the repeat rate, the pitch master, and the left and right channel high frequency filters, the effect becomes transformed by incoming clock information. The parameters then adjust themselves to produce a 'Keystone Kops' accompaniment in time to the beat, with tempo changes adjusting the pitch of the 16th-note arpeggiation in semitone steps. Playing just the snare sound of my test drum pattern through this preset produced enough music to fill the empty gaps between beats, with all the pulsating rhythms of a comic chase from the 1920's silent movies. Again, the snare sound produced a tone reminiscent of an acoustic guitar, and adding a synthesized polyphonic Rhodes sound to the ensemble created a thicker beat with a lot of frenzied action from a glockenspiel-like tone.

The parameters of these variations can be adjusted to produce the simplistic pitch alteration available on inferior digital effects machines, but given the magic of the sounds they create, I can't see any reason to try. As an experiment, I replayed some solo vocals through the 'Major Modal' program and achieved some brilliant results, the Lexicon creating a sort of walking string bass accompaniment.

These programs distinguish the PCM70 as a 'real-time digital re-synthesizer', let alone effects processor.


These include an Auto-Load feature which gives you the option of automatically loading each Program or Register as you call it, or requiring you to press the front panel 'Load' button before doing so. The advantage of the second method is that you can search out a memory location which doesn't have anything important in it before you overwrite it with what you've just been editing (a subtly useful facility).

You can either fix incoming MIDI program changes to incrementally call the Register and Preset Program numbers (the presets start at memory location 50) or to utilise the user-programmable Program Change Table. This table allows you to assign any memory location to any Program Change message. This is an invaluable performance utility, as sounds can be dynamically linked via MIDI to the sort of effects treatment which suits them best, and which may indeed be the same effect! These utilities are accessed in the same way as all the other programs - the minor drawback here being that they must be loaded before you can alter them, forcing you to save any edited program to a Register before doing so.


As you'd expect with such an extensive MIDI implementation, the Lexicon PCM70 responds to, and transmits, MIDI program change messages. It will also transmit and receive system exclusive dumps of both the current Program and the entire Register memory, meaning that if you use a MIDI sequencer you can store your effects along with the relevant songs. Of course, because you can control the PCM70 via MIDI, you can also record yourself doing your controlling with the same MIDI sequencer you are using for your music. Not only does this mean that you can reliably reproduce mega-effects, but it means that the PCM70 fits right in with the current trend towards computer-controlled MIDI workstations.

The system exclusive capabilities have enabled third parties to write software packages which assist the user in getting the most out of their investment. There are programs available for both the Atari ST and Apple Macintosh, from Dr T and Digidesign respectively, which make excellent use of the added power of the microcomputer and mouse to enhance the level and speed of control for the user.


There are an awful lot of digital effects processors around to choose from, making that choice both difficult and confusing. Every year the bandwidth's get broader, the reverb/delay times longer, and the control facilities more extensive. Last month I looked in-depth at Yamaha's latest digital reverb/multi-effects unit, the REV5. I was particularly impressed by the 'density' of the reverb it created and the clarity of its effects in general (far better than those produced by my own machine, a REV7!).

The Lexicon PCM70, however, has shed a new light on my conclusions, and one which I find difficult to justify given its technical specifications. On paper, the PCM70 has a lower sampling rate, effects bandwidth (15kHz) and shorter maximum delay times than the REV5. Yet, to my ears, it makes the REV5 sound too dense and too clear. The Yamaha's effects tend to have an almost super-real electronic presence, as opposed to the subtle acoustic you achieve with the Lexicon. Perhaps it is something to do with having a very fast central processor in conjunction with the slower sampling rate, enabling the PCM70 to perform many tasks in between samples.


- Mono input, stereo output
- MIDI In, Out, Thru

- 33.5kHz, 16-bit linear PCM sampling
- Frequency response:
20Hz to 15kHz (effect)
20Hz to 20kHz (direct)

- Dynamic range of processed signal: 80dB

- Audio input, switchable:
+4dB balanced, 40 kOhm
-20dB, unbalanced, 500 kOhm, via ¼" stereo jack socket

- Audio outputs, switchable:
+4dB, balanced;
-20dB, unbalanced via two ¼" stereo jack sockets.

Footswitch controls: bypass, remote Register select (increments Register preset)

The point appears to be that it's not what you've got, it's what you do with it, and with the PCM70 you can do it with MIDI. Perhaps it's unfair to compare it with the REV5, devices such as the Korg DRV3000, Ibanez SDR1000+ or ART DR1 provide better yardsticks. These all offer real-time MIDI control of effects parameters which, on face value, are similar to those of the Lexicon; they are a lot cheaper; and some can even act as two independent effects units simultaneously. Yet upon closer inspection, and in comparison, these machines offer nowhere near the number of parameters or simultaneous MIDI controllers. Then there are the differences in effect quality, and make no mistake, the PCM70 sets standards rather than tries to meet them. Indeed, its parameters are so varied and wide in range that talk of doing 'two effects at once' is almost meaningless - you can do four or five! In addition, MIDI input is not necessary to provide beautiful sounding effects, it merely serves to enhance their dramatic and expressive potential. This 'layered' relationship, where a program can be approached on a number of levels of differing complexity, makes the PCM70 a unit which can grow with you according to your needs, your ancillary equipment, and your imagination.

As I said at the beginning, this is a device of singular quality which sets a very high standard by which to judge any 'budget' effects unit. Given its price, perhaps it should. Given its specification, it's fascinating that it does, and I cannot emphasise enough how lovely it sounds (even off tape, by which time many a monstrous reverb has drowned in a sea of bass and hissy cymbals). Whether used on stage or in the studio, it seems to me that here is a machine which offers a unique level of expressive potential. I practice what I preach - I'm now trying to make room in my overdraft for one!

Price £1785 plus VAT.

Contact Stirling-ITA, (Contact Details).

Please note that the 'Inverse Rooms' software update is available for current PCM70 owners at the very reasonable cost of £50 plus VAT.

Also featuring gear in this article

Previous Article in this issue

Sonus Masterpiece

Next article in this issue

Practically MIDI

Sound On Sound - Copyright: SOS Publications Ltd.
The contents of this magazine are re-published here with the kind permission of SOS Publications Ltd.


Sound On Sound - Dec 1987

Gear in this article:

Studio FX > Lexicon > PCM70

Gear Tags:

Digital FX

Review by Mark Badger

Previous article in this issue:

> Sonus Masterpiece

Next article in this issue:

> Practically MIDI

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