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Hands On: Lexicon PCM70

David Mellor takes an acknowledged classic effects unit for a road test.

There are those who always want the latest, the most up to date, the flashiest and, perhaps, most expensive car on the market. Then there are those who prefer to own and drive an acknowledged classic, a Mark II Jaguar, perhaps, or an original Lotus Elan. A third group of people will understand the true function of personal transport apparatus and buy a low-mileage secondhand mass market saloon, knowing that it will get them from A to B with the minumum of fuss and cost.

There is a little of all of these ways of thinking in each of us, and it affects the way we see studio equipment too. If you have the latest and the best, then you know that your productions are breaking new ground, and if your work finds favour, then others will follow in your footsteps. If you use a classic piece of musical or studio equipment, then you know that the sounds you are dealing with have proved their worth and marketability thousands of times over. If you follow the third path, you'll be looking to buy a piece of equipment that does the job the way you want to do it at the least cost. This is perhaps the most sensible option. Do you agree?

No, I didn't think you would. 'Sensible' people don't get involved in music; they become lawyers, accountants and college lecturers. Getting the job done efficiently and at minimum cost is not wholly compatible with producing an artistic result which eventually may affect the life and thoughts of those who hear it.

One of the advantages of working with acknowledged classic pieces of equipment is that you can have a great deal of confidence that the sound they produce is right. Some top engineers can trust their ears totally, but lesser mortals like the rest of us find it helpful to have the benefit of other people's judgement. When you have finished a track, don't you always play it to someone you know and hope that they say they like it (and that they won't just say that to be nice)? Another way of getting the benefit of other people's judgement is to use classic equipment. If a particular piece of equipment is well-liked and used by top engineers the world over, then it must be good, mustn't it?


Ask anyone in the know "who makes the best reverb units?", and they'll say "Lexicon do". Lexicon have been producing high-quality digital reverb units for over a decade and their reputation is second to none, although now there are many devices which could make a reasonable claim to be the best unit available. Once upon a time we had to depend on plate reverb units, which were bulky and inflexible, although their basic sound quality was good. Lexicon's early model 224 showed us how we could manipulate the quality of the sound by adjusting the reverberation time separately for high and low frequencies, among other features, even though it didn't, in all honesty, sound that great.

Lexicon's more recent top-of-the-range models have certainly gone far beyond what their earlier attempts achieved sonically, and the fruits of their research filtered down to the more affordable PCM70. The Lexicon PCM70 has certainly been one of the most popular effects units ever, and you will find it in many studios across the length and breadth of the country, and around the rest of the world. If you want to be sure that you are using one of the world's favourite effects units, patch into the PCM70 and you definitely will not be disappointed.


I have already looked at another classic effects unit, the Yamaha SPX90, in a previous Hands On. The SPX90 was the first of the multi-effects units, and could produce just about any effect you were likely to need in the studio. The Lexicon PCM70 doesn't have quite this abundance of effects, but there is nevertheless a little more on offer than just reverb.

Basically, a digital reverb unit consists of a lot of RAM, plus the number-crunching power to shuffle the temporarily-stored audio data about in a way that will create the sound of multiple reflections in a room. With appropriate software, the same hardware can be used to create delay, chorus, phase and flange effects, and the PCM70 does pretty well in these departments too. But first let's look at the way the PCM70 is organised. Once you understand this, you'll be able to dive into the editing parameters and manipulate the programs to get exactly the sound you want.

Figure 1. The PCM70's front panel.

Figure 1 shows the front panel of the PCM70. When it first came out, we were still getting used to the idea of operating equipment which didn't have too many knobs, and all the button pushing was seen as a necessary unpleasantness (though it was the lack of mechanical hardware that made the equipment affordable). If you were an equipment designer and you were trying to develop an interface to a synthesizer or effects unit which used a form of up/down key interface, you would actually find it quite difficult to work out which was the best of the many ways to implement it. Lexicon chose to use a method which isn't at all intuitive, and it is unlikely that you could sit down with a PCM70 and get much joy from it without some serious thought.


On most modern equipment, you can call up the various presets by pressing the up/down buttons, in the direction you want to go, as many times as it takes to get there. Alternatively you may be able to select a preset from a panel of number keys. Either of these methods are very obvious and you don't need to read the manual or attend a seminar to know how to do it. What the Lexicon PCM70 has, at least as far as the preset programs are concerned, is a number of basic algorithms, each of which is given a number from 0 to 6 (you understand, of course, that software designers start counting at 0, not at 1 like the rest of the human race). Select the algorithm by pushing the up/down keys. Each algorithm has a number of variants, as few as two or as many as nine, which are numbered from .0 to .9. These are selected by the number keys. Figure 2 shows the range of preset programs available; if you wanted the Infinite RT program (number 4.7), then you would push the up/down keys until you saw 4-point-something in the display, then number key 7, then Load (unless the unit has been programmed to autoload, in which case the program will load up without further ado).

"In this age of disposable products, it may come as a surprise to learn that the Lexicon PCM70, classic though it is, is still available."

Once you know what to do, this way of working isn't a problem, but it does cause some confusion when you try to select, for instance, Program 2.3. As you can see from Figure 2, there isn't a Program 2.3 and the display will show 'Not available'. Now you know why, but if you didn't have the benefit of a manual or someone to tell you, you might think that Program 2.3 had gone on holiday and might be back later, or that the unit was faulty, or that the unit was awaiting the next software revision, or indeed that you had done something wrong. The answer is not to worry about it.

As well as Program Mode, there is also Register Mode, which is just another way of referring to user memories. Registers are accessed in exactly the same way as Programs, except that you won't get the 'Not available' display. If no program has been stored in a Register, then the display will read 'Unused' or 'Register Unused' showing that there is a free space into which to write your creation.

Figure 2. The Lexicon PCM70's preset programs.


You will probably be wondering why there is no button labelled 'Edit Program', or something similar, on the front panel. To save space and hardware (I presume), the PCM70's Program and Register modes are selected by front panel buttons, with indicator LEDs, and if neither of these modes are active then you are in Edit mode. This is something to watch out for. If you didn't realise you were in Edit mode, you might be frantically searching for a Program or Register and find only cryptic messages such as 'HC MST' or 'L3 RFL DB', followed by a couple of digits.

Like Program and Register selection, you find the parameter you wish to edit by punching the Up/Down buttons the appropriate number of times in the correct direction, and then using the number keys to get where you want to be. You might think this is a bit hit-and-miss, but fortunately the parameters are grouped into families and you can find the precise one you need very easily.


Since the PCM70's primary function is, to my mind at least, as a digital reverb unit, I think I should start with Program 3.0, the first of the 22 basic reverb Programs. The Programs in Row 3 of Figure 2 are designed to emulate real concert halls, and they do a pretty good job too. As the manual states, the reverb starts with a low initial density, which builds up gradually over time. As well as the reverberation itself, the Concert Hall programs also have four early reflections, each of which can be independently adjusted for level and timing. There is also a gate for stopping the reverb abruptly, an effect which was especially popular on drum sounds at the time the PCM70 was introduced, but which sounds a bit naff now.

Stepping down to Row 4 (you press the Down key to change the number) we find the Rich Chamber programs. I can't improve on Lexicon's description: "The Rich Chamber programs produce an even, relatively dimensionless reverberation, with little change in colour as the sound decays. The initial diffusion is similar to the Concert Hall programs, but the sense of space and size is much less obvious. This characteristic, along with the low colour in the decay tail, makes the Rich Chamber programs especially useful on spoken voice, giving a noticeable increase in loudness with very low colour." This is actually a very helpful description of the sound, not just an advertising copywriter's hype, which Lexicon provide in their manual for all the Program families. When you understand the designer's intentions, it makes operation of the unit more rewarding (a lot-more rewarding than simply flicking through presets).

The programs in Row 5 are plate simulations, with a high initial diffusion and bright sound. Lexicon recommend their use on percussion. Row 6 is dedicated to 'creative' Inverse Room programs. Many of the reverb programs have editable parameters in common (see box for details). There is a good range of these, but not, I think, too many to put the average user off editing the original programs. The one drawback is that the unit's display is quite small and some of the parameter names have necessarily been abbreviated beyond the point where people can be expected to work out their meaning — but you have to remember that classic effects units have their failings, just as classic cars leak oil.

The other effects have a whole new set of adjustable parameters, far too many for me to go into here, but I must mention the PCM70's party trick. Every engineer will want to use it at least once, and I recently placed it, suitably tailored, on the opening of the CD The Killing Tide by Sol Invictus. The effect is known as Resonant Chords.

"When the Lexicon PCM70 first appeared, it had one major new selling point, Dynamic MIDI, which allowed you to control effects parameters from a MIDI controller."


Lexicon describe this effect as being "unlike anything that has ever appeared before in an effects processor", and I don't think anything like it has appeared since. The effect is created by six delay lines, each of which has its own delay and feedback controls. As you probably know, if you set a short enough delay time and apply feedback then any input will create a sequence of impulses which recur so rapidly that they are heard as a musical note. Multiply this by six and you have the ability to create chords, so that each bash of the snare drum will produce a burst of harmony at the output.

You could probably achieve the same thing with six delay units, but Lexicon have been thoughtful enough to allow the user to program in musical notes, so you can program a chord very quickly rather than having to tune the delays very precisely. Each of these short delays with feedback is preceded by a longer delay, so that the six notes can emerge in a rhythmic sequence. Once you get started on editing these programs, it's amazing what you can do, even if it is really a novelty effect. Don't forget to try the 'Auto Suspense' program, which Lexicon advise "is great for daytime soaps".


When the Lexicon PCM70 first appeared, it had one major new selling point, Dynamic MIDI, which allowed you to control effects parameters from a MIDI controller. Nowadays this is considered something that every serious effects unit must have; the only problem is that hardly anyone ever uses it. The blame for this lies with the manufacturers, who, on the whole, spare no effort to produce brilliant equipment, and then don't bother to show us how we can get the best out of it. It is human nature that if something is difficult to understand, then we are reluctant to put time and energy into understanding it unless we can see clearly what the reward is eventually going to be.

I would recommend to any manufacturer of effects units which incorporate the equivalent of Dynamic MIDI that they program in a few presets which use it and, most of all, explain prominently in the manual what we are supposed to hear and tell us how we can get the best out of the feature. I have tried using it from time to time, but I always found my results interesting only in an academic sense; up until very recently (yesterday in fact) I hadn't met one person who had used Dynamic MIDI or the equivalent function on another effects unit. But this one person who does use it has an application which does indeed appear to be musically interesting (thank you, Steve Culnane). The trick in this case is to use a flanging program on the PCM70, with the depth of the flange controlled inversely by note-on velocity, so that the more quietly the keyboard is played, the more effect is added, which makes all the difference between a dull ordinary piano sound and one with life and sparkle.

Let me explain a little about how to use Dynamic MIDI yourself: each Program has 10 patches available by which a MIDI control source can change a program parameter. In Edit mode (which is when neither the Program nor Register LED is illuminated) Row 5 of the display is given to MIDI patches, and it would be most logical to start at position 5.0. If you spin the soft knob now you will see the possible control sources, which as well as MIDI controllers such as the pitch bend and modulation wheel — and all the rest — can be note on velocity, aftertouch, note number of last note played, or even MIDI clock rate. When your chosen control source appears, press the Load key. Now you can select the parameter you wish to control. Once you have got this far in PCM70 operation, it isn't difficult to get the hang of the other Dynamic MIDI operations, and with patience almost everything you could imagine yourself wanting to do is possible.


In this age of disposable products, it may come as a surprise to learn that the Lexicon PCM70, classic though it is, is still available (at £1,792 plus VAT). It just goes to show that if you have a quality product, and support it with software updates, the customers will keep on coming back. The PCM70, even against modern competition, is still a wonderful piece of equipment and I have no hesitation in recommending it, not only to buy, but also to feature in questions you might ask any studio you were thinking about booking. The question is "Do you have a Lexicon PCM70?", and an affirmative answer will tell you that the studio is, at least in respect of its effects rack, properly equipped.

The Lexicon PCM70 was kindly supplied lor this article by Audiohire ((Contact Details)).


Aftertouch or Velocity to Reverb Time
Any controller to Reverb Time
Any controller to Feedback
Pitch Wheel to pitches in Resonant Chords
Any controller to Mix
Note Number to Pitch Master in Resonant Chords


Attack: Sets the sharpness of the initial response
Chorusing: Randomises delay times, adding richness to the sound.
Decay: Optimisation alters program characteristics according to input level to make the reverb decay more natural. This can be set On or Off. Select the off position if clicks are noticed.
Definition: Controls the build-up of echoes during the latter part of the decay.
Diffusion: Controls the density of echoes.
Delay Master: Changes simultaneously the delay times of all the early reflections.
Duration: Determines the length of time before cut-off in the Inverse Room programs.
Gate: Sets the time delay before reverb is stopped.
HC (high frequency cut-off): Applies a 6dB/octave filter at a selectable frequency.
Lo Slope (low frequency slope): Determines the shape of the reverb envelope at low frequencies in the Inverse Room programs.
MD Slope (mid frequency slope): As above, but for mid frequencies.
L RFL DB (left early reflection levels): The level of each early reflection in the left channel can be adjusted.
R RFL DB (right early reflection levels): Similar to the above.
L RFL MS (left early reflection delay times): The delay time of each early reflection can be adjusted.
R RFL MS (right early reflection delay times): Similar to the above.
LVL MST (level master): Allows simultaneous changes in the early reflection levels without altering the relationship between individual reflections.
Mix: Controls the ratio of dry and processed signal.
PDelay (Pre delay): Sets the time between the input signal and the onset of reverberation.
Reverb Time: I think you know this one already.
RT HC (reverberation time high frequency cut-off): Sets the frequency above which sounds decay at a progressively faster rate.
RT Low: Adjusts the low frequency reverberation time.
RT Mid: Similar to the above.
RTL Stop: Sets a separate reverberation time for low-frequency signals when input has ceased.
RTM Stop: Similar to the above but for mid frequencies.
Size: Sets the room size.
Xover (crossover frequency): Sets the frequency at which the transition from low-frequency reverb time to mid-frequency reverb time takes place.

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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 - Jul 1992


Effects Processing

Gear in this article:

Studio FX > Lexicon > PCM70

Gear Tags:

Digital FX

Feature by David Mellor

Previous article in this issue:

> Quality Control

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> Some Like It Hard

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