WHERE TO USE PROCESSORS AND WHY
Delay, originally called echo, is one of the oldest artificial effects, yet it can still be one
of the most impressive - if used with care. PAUL WHITE explains the potential
problems and how to avoid them.
Delay, in its analogue tape guise, was one of the earliest special effects to be used in audio recording, often to
add interest to guitar or vocal sounds. With modern digital delays we have much more control over decay time
and tap (repeat) spacing than with tape delay, not to mention a much better frequency response and a lower
noise floor. However, as regular readers of this series will appreciate, even the best effects can detract from a
recording if they're not used very carefully, and digital delay is easy to misuse.
MUSICAL DELAYS
Most of us know what a delay unit does, but what exactly is a delay in musical terms? A delay device repeats
the original sound one or more times, so the musical outcome is to add more notes to the performance, at time
positions later than the original. This highlights a potential problem right away -- if you have a very pronounced
delay and the delay time doesn't fit in with the tempo of the music, the delay may upset the musical timing of the
piece. If the piece has a fixed tempo it's easy enough to calculate the delay time needed to get the repeats to
fall on the beat (for example, if you're working at 120bpm you need 60/120 or half a second), and you can
double up or halve the delay time without going out of time with the song. Even so, you can still run into trouble,
because now the delayed note might clash musically with the new note it coincides with.
Part of the problem is that digital delays produce almost perfect
copies of the original sound, whereas tape delays had a
spectacularly poor frequency response which made the delays
seem more like natural echoes. We're in the realms of
psychoacoustics here -- if the delay is quieter and duller-sounding
than the original, we accept it as an echo, but if it's equally loud and
just as bright, it's simply a note in the wrong place. Echoes that
occur in nature get duller every time they reflect from a new
surface, so to get the same result from an electronic delay line we
need to try to emulate this. Simply feeding the delay return back
through a mixer channel with the top rolled off doesn't produce
exactly the same effect, because every delay will be equalised in exactly the same way, but it's still a lot better
than nothing. However, to really do the job properly, the EQ needs to come after the delay line, but before the
feedback path used to create multiple repeats. Some of the better multi-effects units provide a delay damping
parameter to simulate this, but there is a dodge you can try if you're using a very basic DDL (Digital Delay
Line). See the 'Delayed Gratification' box for details.
COMPLETELY TAPPED
Multitap delays are useful in situations where you don't want to be forced to make the delay time match the
tempo of the song. If you time the various delay taps so that they are not exact multiples of each other, the delay
pattern should be complex enough that the listener's brain gives up on trying to match it to the tempo of the
music. (For a good example of this, listen to the echo used on '60s instrumental guitar music. The echo gave
the guitars a big sound, but there was enough apparent randomness in the effect not to upset the listener's
perception of the tune's timing.) Feeding the output of all the delay taps back into the DDL input causes the
repeat pattern to rapidly build in complexity as it decays, rather like a very coarse reverb effect. By the same
token, if you need to create a multitap delay that reinforces the tempo of a piece of music, all the tap times must
be multiples of the tempo -- though, of course, you could set some taps to straight time (quarter-notes,
eighth-notes and 16th-notes) and others to triplet time.
What happens if your song contains tempo changes? Obviously, if you have a fixed delay time this will throw out
the synchronism between the delays and the music, but if you're using a programmable effects unit you can
create a new patch at the new tempo and switch to this, either manually or via MIDI, at the appropriate time.
Unfortunately, many effects units fail to change patches smoothly, so how well this works depends a lot on the
make and model of your effects unit. Ironically, the cheaper ones often change patches more quickly than the
expensive ones, as they're running less complex algorithms.
A much nicer way to tackle the sync problem is to use one of the increasing number of effects units that allow
you to sync delays, LFOs, and so on, to incoming MIDI clock. Providing you have a sequencer running, you can
force the delay timing to precisely match any tempo changes you might make.
TOO PURE FOR COMFORT?
Those old tape delays had terrible technical specs, but they still produced a wonderfully warm sound, and their
limited bandwidth was only one of the reasons. Another reason was the rather poor stability of the tape
transport -- musicians would leave their echo units in the band's van for days, with the rubber pinch-roller
pressing against the capstan all the time. Often this would create flat areas on the pinch-roller, and the result
was slight speed unevenness in the transport -- so instead of producing super-clean repeats, the tape delay unit
would apply a tiny amount of vibrato to them, pretty much by accident. You can simulate this sound with a
multi-effects unit by placing a chorus or vibrato block before your DDL, but keep the effect very subtle, otherwise
the 'chorusing' will be too obvious.
In a real tape echo, every time a repeat is fed back and re-recorded, more vibrato is added, making each
repeat messier than than the one that went before. To emulate this exactly using a digital DDL, you'd need to
put the chorus effect between the feedback loop and the delay line input, but many algorithms don't permit you
to do this. That being the case, just a little chorus before the DDL will get you close enough.
MORE PSYCHO-ACOUSTICS
In real life, there's no such thing as a clean echo -- each echo will have some ambience because of the multiple
reflection paths the original sound creates. To emulate this electronically, we need to add a hint of reverb to
each echo. The easiest way to do this is to place a reverb block after the delay block. You don't necessarily
need a very long reverb to make this technique work, but as a special effect a reverb of up to three or four
seconds can sound quite spectacular. By varying the reverb mix parameter, you can adjust the balance of clean
delays against reverbed delays, and in music that is sparse enough to let you appreciate these subtleties, the
added sense of space can be very worthwhile.
Yet another complication when using delays is that, when there's a
lot going on in a given piece of music, delays can just clutter up the
sound, yet in a less busy section the echoes may not be dominant
enough. One answer to this is to use ducking delay -- a delay that
drops in level when there's a strong signal, and comes back up in
level during pauses or quiet passages. You can achieve this by
setting up a compressor or gate in ducking mode, then feeding the
delay unit through the ducker, triggering the ducker from the dry
signal. [If you don't know how to set up a compressor as a ducker,
take a look at the article on using compressors that we ran in the
April 1997 issue of SOS. This features a box and diagram to
explain how it's done -- Production Ed.] These days an increasing
number of effects units now include ducking delay and reverb as
standard, and having the solution already inside your effects unit
makes life a lot easier and saves patching. It also means that you
don't have to tie up a gate or compressor that might be better used
elsewhere in the mix.
DELAYING TACTICS
I seem to have got to the end of this month's instalment, but the
bottom of the page is still some way off -- so to avoid leaving a
long and embarrassing expanse of white paper, I'd like to share
with you one of my favourite effects patches, which relies on some
of the principles discussed so far. This is an interesting
delay-based multi-effect that can be used to create a sense of
space and distance, without making the mix muddy. It works best
on percussive musical sounds such as piano or acoustic guitar
samples, though it also suits electric guitar pretty well. The block
diagram is shown in Figure 2, but I'll talk you through it anyway.
The signal chain starts with a high-pass (low-cut) filter to
attenuate everything below 500Hz. Most multi-effects units now
feature a selection of filters, and if yours does you should choose a
simple shelving low-pass type and set maximum cut at 500Hz. If
you don't have this option in your effects processor you can always
patch a hardware equaliser before the effects unit.
Next you'll need the slightest hint of chorus, vibrato or pitch detuning, depending on what your machine has to
offer, after which you feed the signal into a stereo delay block. It's important here to use a delay block which
allows the two sides to be set up separately, as one side needs a 1ms delay, to give a sort of static flanging
effect, while the other side can be set anywhere between 300 and 700ms to produce the necessary echo.
Set the feedback for both at between 60 and 70%, then finely adjust the feedback on the 1ms side so that you
can just hear a metallic filtering effect colouring the sound. Play solo piano notes to check this.
Now take the delay outputs and feed them into a stereo reverb, set for around three seconds decay time with
between 50 and 100ms of pre-delay.
Set the reverb mix to 50% and you're in business. If you've got it right, a single piano note should bounce away
into the distance in a pleasingly ethereal manner. This effect works particularly well with an Alesis Quadraverb,
but I've also set up a similar thing on the Lexicon MPX1, and the result was almost as charming and significantly
cleaner.
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