This article was also published in Electronic Soundmaker & Computer Music, August 1985, and first available on mu:zines here:-

How To Do Tricks With Time (ES Aug 85)

Why Digital?

Despite all the worthy effects that the old analogue delays could give, the advent of digital recording and synthesis has meant that there has to be a higher fidelity delay system to match. Quite simply the quality of 16-bit digital technology (like that used in the new SDE-2500) completely does away with the signal-to-noise and regeneration problems previously associated with delay effects. But digital delays can offer a lot of effects which had to be found elsewhere in the past. Because of the extraordinary faithfulness to the original signal, effects which rely on phase relationships, where two identical signals are slightly separated by a time difference, can be faithfully recreated using a digital delay.

Phasing

Clearly one of the easiest effects to create using very short delays. The technique is to delay the original signal so that it is out-of-phase (or to put it another way out-of-sync) with itself, but not so much that it sounds 'out' with the timing of the track. To achieve this it is necessary to stay in the approximate time area which the wavelength of the sound occupies, or somewhere between 1 & 30 milliseconds. In this area the two signals 'interface' with each other in a fairly subtle way. So subtle in fact that you can't really hear it unless the phase is changing: the human ear is much more sensitive to change in a sound. The phase change can be done on delays which have a modulation section (like the BOSS DE200 for example). By using a slow rate between 0.5 and 1.5 times a second — and not too much depth, you will get a nice slow phase effect. Too fast with the modulation or too much depth and you start to get into the area of chorusing/flanging.

Chorus

This effect takes its name from the extremely complex and unpredictable effects which you get when a large number of instruments (strings for example) are all playing the same line. In this situation, the effect is produced by numerous small variations in tuning and phasing. In order to imitate this complexity, we use a fairly short delay again but make the modulation happen much faster than in phasing. However when setting this up you will find you will need to be careful, particularly with the depth of modulation. Otherwise the effect will be more suitable for imitating the Portsmouth Sinfonia than the London Philharmonic. Too much modulation effect will simply put the instrument you are processing out-of-tune in a horrible wavering manner.

Flanging

Originally created by slowing down and speeding up the analogue delay machine (usually a Revox or some other half-track) often by touching the spools of the tape recorder, acting as brake. Again a phase effect, although somewhat more radical, we can achieve it on a DDL by a short echo, modulated more slowly than chorus, but with a greater depth of effect. This slow modulation should produce the characteristic swooping up and down of the flanger.

ADT

Automatic Double Tracking (as opposed to simply recording a part twice on two different tracks of a tape recorder) is another commonly desired effect. Because with this we are imitating two instruments (instead of many as in chorusing), we would use a longer delay so that the ear can separate the two notes, but only just. Delays between 50 and 150 millisecs are good for this, again depending on how obvious you want the doubling to sound.

Echo

One thing the old analogue tape delays did really well was realistic echo effects. This is because high energy frequencies (ie the top end) are the ones which die away first in natural acoustics and they are also the ones which are most easily lost on tape (especially when it's a bit old and worn). One problem with DDL's can be that they are too good to reproduce a 'natural' echo. However, some of the most recent (like the SDE2500) have a filter which can be applied to the delayed signal, which just rolls the top end of it (making a bit less bright), to give an authentic echo feel, but taking advantage of the higher quality of digital reproduction.

Sampling

Of course, the technology which is used in digital delays is exactly the same as that in the new field of sampling which is becoming extremely popular in music these days. As a result some of the DDLs you can now buy (like the BOSS DE200), have the ability to work like samplers. You can actually 'capture' a sound and then, most exciting of all, you can use the sort of trigger that a Doctor Rhythm can provide to 'fire' the sample together with a rhythm pattern. It's great fun and you can really add a new 'quality' to your music, beefing up the snare drum with percussive samples or even triggering repeating basslines.

All in all then, the DDL is capable of a lot more than just straight echo effects.

In that one package there are a lot of useful effects to be found. In this space we haven't had a chance to cover all the possibilities, so keep experimenting — there's a lot of things in a DDL just waiting for you to find them.