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Echo Unit Supplement

Enter The Time Domain

Add Another Dimension to Your Sound!

"Wee represent and imitate all Articulate Sounds and Letters and the Voices and Notes of Beasts and Birds. We have certaine Helps, which sett to the Eare doe further the Hearing greatly. Wee have also diverse Strange and Artificiall Eccho's, Reflecting the Voice many times, and as it were Tossing it; And some that give back the Voice Lowder than it came, some Shriller, and some Deeper; Yea some rendring the Voice, Differing in the Letters or Articulate Sound."

It's tempting to believe that, in writing 'New Atlantis', seventeenth century polymath Francis Bacon had some vision of the musical technology available to the composers of the twentieth century. Yet his speculations on Sound Houses and other diverse instruments stem more clearly from an unconscious appreciation of the importance of echo and reverberation to the composition of satisfying music.

The long tradition of sacred music has always made use of the 'celestial' effect of reverberation produced by large spaces enclosed in stone walls, and European classical composers simulated the natural echoes of mountains and stone corridors in their pieces. Vivaldi's 'Four Seasons' is just one example of a piece containing an 'echo' passage, where the leading melody is repeated by other instruments after a few notes' delay. The organ compositions of J. S. Bach and many others used echo effects produced by repetition from upper to lower keyboard.


Early recordings on disc, cylinder or wire usually employed a single-point recording device (such as the acoustic horn of the first Edison machines) which was naturally prone to reception of reverb from the recording studio. As sound damping, recording techniques and direct injection of sounds from pickups improved, however, the naturally reverberant sound of live music was lost. It became clear that it would have to be re-introduced artificially, and the rapidly developing science of tape recording represented an ideal medium for the production of repeat echoes.

Tape Echoes

Early electronic echoes, then, were tape-based. The WEM Copicat for instance relied on a 15" loop of ¼" tape, a single erase and record head, and three replay heads situated at about 1" intervals inside the tape logs. Combinations of playback heads and different tape speeds could give many echo effects, from single or multiple repeats to a fast reverb-like sound, with the inevitable colouration produced by progressive distortion during re-recording. The Copicat, the HH tape echoes, Binson and Carlsbro models and the Echoplex became highly popular, the latter particularly for its ability to give very long delays and a sound-on-sound effect. Vivaldi's string pieces could now be reproduced by a single musician playing solos over his own backing played a few seconds earlier; guitarists Steve Hillage, Brian May and many others have created amazing passages using this method.

Studio quality tape units such as Roland's Space Echo became standard issue for PA work, and the tape echo still has a place in many studios and bands. In this supplement we've reviewed a recent model, the Evans SE-810 echo unit.

Analogue Echoes

Tape echoes suffer from the inevitable electro-mechanical problems associated with motors, springs, moving tape loops or discs and pads or wheels under tension. Although they are accurately described as analogue systems — since the input information is copied in its original form for processing — an electronic analogue system was actively sought in the 60's and 70's to avoid these electro-mechanical problems. With the introduction of BBD chips the answer seemed clear.

The Bucket Brigade Delay or BBD chip contains a series of tiny capacitors, which charge up when an input signal appears, and discharge their signal to the next capacitor in line until an output appears. Since this charging process takes a finite amount of time, a delay is imposed on the signal. This can be mixed with the input to create a single echo, or returned to the start of the bucket brigade to create repeat echo. Chips usually contain multiples of 1024 buckets, and are economical when used for short delays in the order of 100mS. BBD devices are capable of giving a few additional features, such as Doppler or Leslie effects. We've looked at another Evans unit, the MX-99, based on the BBD system, and also at two JHS Echotec models.

Digital Echo

The problems of BBD designs included cost, if a large number of chips had to be used to gain long delays, quality, which tended to suffer from the BBD's limited frequency response, and versatility, which wasn't sufficient for the increasing number of studio tricks which had come to be expected in the 70's. The only foreseeable solution was to completely digitise a musical signal and produce effects by manipulation of this information. Although this was done with computers such as Peter Zinovieff's at EMS some time ago, it wasn't until the mid-70's that digital controllers became inexpensive enough to fit into standard studio equipment.

Once it was possible to replace the power-consuming BBD shift registers with efficient RAM storage, an enormous number of effects became easily accessible. Manipulations within the time domain (to create reverb and echo) were now joined by pitch and phase alteration (phasing and vibrato) and various forms of modulated short delay and filtering (chorus and flanging).

Flanging, originally produced by replaying two identical tapes and varying the speed of one by pressing down on the flange of the tape spool, could now be produced with a delay of 1-10mS, varied slightly in duration in a regular fashion and remixed with the original. Digital echoes examined with a built-in modulation section to produce such variation include the Ibanez DM 1000 and MXR II units.

Automatic Double Tracking or ADT uses a 10-45mS delay to give an almost inaudibly fast repeat of all the music input. The effect produced is that of two instruments playing together. Most of the units examined this month, including the Cutec CD-242, DeltaLab Effectron ADM-64 and Roland SDE-2000 will produce ADT.

Chorus is similar to ADT, with slight rate variation of a delay around 50mS. Again, any of the units reviewed which has a modulation section or provision for external modulation can produce this sound-thickening effect. Similar remarks apply to Vibrato, the variation without feedback of a delay around 25mS.

Echo itself depends largely upon the maximum delay obtainable on any given unit. Delay costs money, and there is still a trade-off in operation between maximum delay time and frequency response. The MXR II unit reviewed here will give over 3 seconds delay, but with a maximum frequency response of only 4kHz. The Korg SDD-3000, on the other hand, can provide around 1 second of delay with 17kHz response.

Programmability. Microprocessor-based delay units can also be equipped with memories to store different echo programmes, making it possible to reproduce a desired studio effect at any time. Examples include the Korg unit mentioned above, and the Ursa Major mentioned below.

Reverberation. As recording quality improves, the demands for a clean reverb sound become more stringent. Spring lines are generally not sufficient, although the Evans SE-810 reviewed here can produce some impressive spring reverb effects. Echo plates in an acoustically isolated chamber are efficient, but bulky and expensive to purchase and install. The solution is a digital unit dedicated to reverb — a very fast series of pseudo-random, overlapping echoes — and we've looked at several devices intended for just this purpose. The Fostex 3050 is an inexpensive, popular, basic reverb unit; the Yamaha R1000 is the prototype for a slightly more up-market unit with various modes or reverb times selectable on the front panel; and the Ursa Major 8X32 could be described as the guv'nor of digital reverbs, an expensive but enormously versatile, state-of-the-art programmable unit.

The Time Domain

Between these 13 units we have covered almost every design, function, cost and facility available on the market. From £70 starters' units to the top professional models, and looking ahead to items not yet available but sure to make their mark on the commercial scene, we've examined them all. We hope you enjoy your journey through the Time Domain.

Previous Article in this issue

Music Maker Equipment Scene

Next article in this issue

Ursa Major 8X32

Electronics & Music Maker - Copyright: Music Maker Publications (UK), Future Publishing.


Electronics & Music Maker - May 1983


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Echo Unit Supplement


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