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for fx sake...


Dave Blake has an Attack of Delirium Tremolando.

MXR, Roland, Bell and Electro-Harmonix ADT Boxes Reviewed by Dave Blake

Our Editor is a lovely chap, charming, mysterious, bless his cotton sox, a poppet, couldn't do without him, blah blah, sycophant, sycophant... BUT when he suggested I take a look at these four onstage fx units, I evinced a certain reluctance, ennui, a dollop of boredom, and even what might be described as a rough and ready truculence. I was lofty and declared, 'I do not like fx. They are boring and tasteless and have nothing to do with music... sir'. Then he hit me.

So: subjectivity time. The reason I do not generally like fx has to do with the Five Minute Syndrome — that is, most fx are interesting for the first five minutes, during which time experimentation proceeds at a fantastic rate, if somewhat heuristically (from the Greek: a system of education in which pupils learn by sussing things out for themselves). Then the ardour cools and moderation sets in. The effect can then be used as a tool to explore new sounds, relieve the musician of dogsbody chores like double tracking, and so on. Often, however, the Five Minute Syndrome does not abate, and the effect is used forever after to generate silly noises. If this strikes you as a bit controversial, write in and discuss. SI is nothing if not a forum.

However, dogmatism is no good thing. Having had a few heuristic days to putter about, I am prepared to admit that fx can be great fun. In the absence of scope pix, noise tests, and other objective procedures, my testing apparat was: the four fx units, a Strat, Les Paul, Kimbara FQ guitar, a brace of Calrec mikes, an EMS synth, a piano, and a Redmere Soloist amp. Also briefly used were: an Avon bass guitar, a Gibson acoustic (bottleneck), a Pignose, my voice, and a certain lady's voice. In the course of testing, I discovered one paramount point: that each unit, like every guitar and amp, has its own specific character. When I began, I naively assumed that four ADT boxes should all do the same job and sound similar. This is no more the case than it is with guitars and amps. The four units, ranging in price from £40 to over £200, each have their own subtleties, vices, and outstanding characteristics. It follows, then, that shopping for an ADT box is not merely a matter of price; it becomes a personal and subjective exercise (heurism rears its head yet again). Thus, my appraisal of the units should be regarded as a springboard from which to dive, and not a series of edicts.

But first a few words about ADT itself. ADT stands for Automatic Double Tracking and began its life as a studio effect intended to 'thicken up' and 'richen' vocal and instrumental melody lines. In days of yore the vocalist (or whoever) was simply required to sing the part over again on another track. This was difficult and time-consuming because the idea was to nearly duplicate the original track - not to harmonise or sing a counter-time. Richard Elen tells the story of one singer he recorded who knew his timing and tuning so well that it took seven takes to get a track bad enough to be useful. And this is the essence of the matter: the ear discriminates between simultaneous sounds in three ways - by differences in amplitude, frequency, and direction. Anything more than tiny differences in amplitude in dissimilar sounds and the balance can be lost (if similar, one sound simply swamps the other). Frequency differences mostly sound out of tune unless they are so great that they become harmony. And directional differences are difficult to reproduce electronically. So the fourth discrimination function comes in: time. Exactly similar sounds can be discriminated by the ear if they happen at different times, and since the ear is very sensitive to temporal shift, this time difference need only be a few milliseconds.

So the problem of ADT is to split the original signal and delay one part of it. Exactly similar sounds in terms of pitch, volume, and direction then become two sounds to the ear. In the studio, this was first done with tape machines, one signal being delayed before being recombined with the other. Later, the IC chips appeared, the 'bucket brigade' devices used by most ADT units. The input signal is split; half is passed straight through as the 'original', while the other half is sampled at regular intervals (determined by an oscillator clock) and held without decay by the series of BBDs for a delay. When the sample is released by the BBD, a time differential is established between original and delayed signals, which the ear hears as two discrete sounds. If the delay time is short, a reverb effect is heard. When the delay time is longer and if some of the delayed signal is sent back to the input for redelaying, a multiple echo is heard. In between, a single sharp 'slapback' echo can be set up. And of course, if the delay time is very short and the delayed signal is at a similar amplitude to the original, the effect is of two voices singing together, ADT.

Simple, innit? Nope. There are other factors to be considered. For instance, frequency is itself a function of time - the standard A is 440 cycles per second. If the cycles were speeded up or slowed down, the note would no longer be A. So if the BBDs released their samples faster or slower than they picked them up, the frequency of the delayed signal would change, and if the release rate varied according to a sinewave, a significant pitch deviation would result. This obviously opens up a whole new world of fx. If you can establish a time delay and a pitch deviation, the ADT sounds that much more authentic, and if the delayed and/or deviated signals can be redelayed, you have a chorus effect. If the pitch deviation is minimised but the delayed signal is repeated under a sustained note or chord, the effect is similar to a tremolo: a fast volume variation.


This is by far the most expensive unit of the four — and it must be one of the most expensive onstage fx units available! It is also the simplest to use and, to my mind, the best of the four. It is totally without frills; a simple cast metal box, standard jack input and two outputs on one side, three uncalibrated black knobs and a push-switch on the top. Like all these units, the MXR needs an AC mains supply and, if I had to level one criticism at the unit, it would be for the five foot mains lead. Unlike the other units, the user's manual is explicit and well-written, setting out theory, controls, and suggested usages. A soft self-adhesive rubber sheet is supplied because the unit has no feet.

The MXR generates very little noise (often a major problem with fx units) due to its use of a compander IC which compresses the signal for BBD processing and then expands at the output. The delay range is from 33 to 500ms, again the best of the bunch. Like all the other units, the MXR is analogue (as you might gather from its name) — that is, the BBDs work directly on the input signal instead of converting it first into digital words. The advantages of digital delay are longer storage time, lower noise, and no clocking noise. The advantage of analogue delay is in the exchequer.

The three MXR controls are designated Delay, Mix, and Regen. The first controls the delay time, the second the proportion of original or dry signal to delayed signal - and on the MXR extreme counterclockwise setting blocks all delayed signal while extreme clockwise suppresses the initial dry signal - and the third controls the amount of delayed signal sent back to the BBD input for redelay, in other words, the number of echoes. The footswitch is obviously effect on/off. The input will accept any high impedance signal, instrument or mike. If only one output is used, the Mix control acts as above; but if both are used, the Mix routes the dry signal to output one and the delayed signal to output two. Thus, by using two amps, a stereo effect is achieved.

The MXR is a delight to use. It really is a delay box and I found considerable fascination playing guitar against a long delay and regen a la John Martyn. The echo was comparable to the best onstage tape-loop units, while the reverb was a good deal quieter and less distorted than the average springline delay. It ADT'd cleanly and, although it will not do chorus or vibrato (vibrato can be obtained by manually tweaking the delay control for pitch deviation, but this is not really practical), it can be set to over-regeneration and siren-like pitch deviation, both of which are interesting in very short doses. Altogether, a spot-on device and my personal fave, even in the face of the high price.


I did not immediately like this unit. It struck me as boring. It was only after the Five Minute Syndrome had passed that I realised what a nice (in both contemporary and archaic senses) unit it is. It is subtle. You don't get a blast of cosmic infra-noise as soon as you turn it on. It sneaks up on you.

Typically Roland, it is beautifully constructed in a cast metal enclosure ('box' is too crude a word for the sculptured design) with all the controls clearly labelled and easy to use. Primarily a chorus/vibrato (real pitch vibrato) unit, it will put out a creditable ADT performance and even attempt a reverb. Richard Editor informed me that he used it to good effect on Keith Mansfield's albums to put a Wurlitzer electric piano into stereo and to sweeten up the chords — so I immediately miked up the Blake Joanna and gave it a bash. Lovely. All the harps of Paradise. And it turns a mere monophonic synth into something else (what? an artichoke? a candied ostrich navel?)!

Not quite as noiseless as the MXR, the Boss was still very quiet. The controls are slightly more complicated than the MXR, but because of the careful layout, they are just as convenient. The input and stereo outputs are standard jack sockets (but no balance or pan control as on the MXR). A switch changes the input sensitivity from 10mV to 80mV and a rotary level control works in conjunction with a peak level LED to give ideal input conditions for almost any high impedance source. Chorus intensity is governed by a rotary, as are vibrato depth and rate (pitch deviation and speed respectively). A footswitch changes chorus and vibrato and an LED displays vibrato rate or a slower speed for chorus. Another footswitch (with plenty of room between the two) changes effect and normal. A rocker mains switch and eight foot lead complete the picture. Like the other three units, the Boss is sold in the UK as 220V, so watch it. That's all, just watch it.

Production models will have slight graphics modification


This set-up was very much the oddball of the four, partly because it is a combination of mains module and fx module, and also because it sounded much closer to a flanger than the other units. Instead of using a variable delay as does the MXR, the Bell uses only a sinewave-controlled pitch deviation, so that phasing fx are much more obvious, while delay fx are minimal. To be honest, I don't regard this unit as an ADT box at all; it is an effect. Even with a tiny pitch deviation, the phasing is audible, while at extreme deviation the sound becomes noise. I did get some unique sounds by playing fretted guitar harmonics, and the vocal fx can be spectacular (if y'like that sorta fing, tosh). By and large, though, I can live without this unit.

It was certainly easy to use in mono or stereo, having only one control of any pith or moment, that being the Deviation control. But I have one monumental criticism. The ADT is not self-powered; it has to be linked to the AC mains Mother unit - along with several other Bell fx boxes if you like. The linkage is via 5-pin male-to-female DINs on the sides of the folded metal boxes. Obviously DINs alone would be weak and unreliable, so the linkage is 'strengthened' by a pair of nylon tabs on one box which fit into spring-loaded clips on the other box. This linkage is slightly flexible so that, as the Bellman explained, the boxes are stable on an uneven floor. Fine, but when you put your foot down to press the fx on/off switch, the weight flexes the DIN linkage and you get a bloody great power crack up yer amp and through yer cones. Bad news. I would much prefer to see an inflexible linkage which would still be perfectly stable on an uneven floor - I direct your attention to the HH system of linking bars in front and rear grooves with heavy knurled nuts for locking.


The cheapest unit, but not to my mind at a disadvantage. I really kinda like this little box. Despite its being much more lightly constructed than the others and despite the rather cheapo knobs, it was simple, adequate, not too noisy, and the pitch deviation seemed far less raucous than the Bell unit. Definitely a box for guitarists, it was not that happy with voice or synth or piano, but as a jangle-box to make your pitiful six-string sound like several 12-strings, or as a vibrato unit, it was fine. In fact the vibrato was so effective at extreme speed and depth that it created an arpeggio illusion. Being essentially a pitch bender like the Bell and Boss rather than a delay line like the MXR, its ADT sounded a bit flangey, but the unit tackled every job, save echo, with a will, and if I sound like I'm rooting for the underdog, this is because I am.

The input is a standard jack socket, high impedance, and while it is not really stereo, it does have a direct output as well as a 'clone' output so that you can drive one amp or channel dry and the other with fx. High frequencies can be emphasised by cutting in the 'Edge' slider switch. Rotary controls are Chorus/Vibrato (infinitely variable between the two, so that there is an area of almost-both), Rate (speed), and Depth. A footswitch controls fx on/off. The mains cable is about seven feet long and - tiny point — is white so you can see it on a darkened stage. Because of its low price and light construction, the Clone's reliability might be suspect; however, since the performance was so good, I am inclined to give it the benefit of the doubt.

Electro-Harmonix seem to go out of their way to bill themselves as 'electronic guerillas', all alternative-ish in their New York Rock Factory. At the recent trade fair, I met a gent who is high up in the E-H hierarchy, and he was about as much an electronic guerilla as is Jim Marshall or Ted Heath. Mind you, I liked his suit and I like his products, so why worry? E-H gets it right and, for the price, top marks!

MXR Analog Delay mk II £203.66/$299.95
Roland Boss Chorus CE1 £127.1 1/$225.00
Bell Electrolabs ADT £81.94/not available in US
Mother £24.95/not available in US
Electro-Harmonix Clone Theory £37.56/$80.00

Dave Blake is an ex-session musician who has been writing on sound for several years.

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EMS Computer Studio

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Electric Wood

Sound International - Copyright: Link House Publications


Sound International - Oct 1978

Donated & scanned by: Mike Gorman

Review by Dave Blake

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> EMS Computer Studio

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