Sound Workshop
Technique : Effects / Processing
Whether you're a beginner or a seasoned pro, there's always something to learn about adding colour to your mix.
 |
The world of audio effects is one that can be
confusing even for experienced engineers. Especially in modern
computer-based recording systems, there's a bewildering array of
options, and to add to the confusion, some effects are widely referred
to by more than one name. In this article, I'll take you through the
most common effects, explaining how they work and where you might want
to use them in your music. Meanwhile, SOS's team of writers has
contributed a wealth of expert tips and tricks, which you can find in
the boxes scattered through this article.
Let's begin by getting clear on what we mean by
'effect': an effect is a device that treats the audio in some way, then
adds it back to a dry or untreated version of the sound. Echo and reverb
are obvious cases, and you can use pitch-shift and pitch modulation in a
similar way. 'Processors', by contrast, generally are those devices
that change the entire signal and don't add in any of the dry signal.
Things like compressors and equalisers fall into this category: as
you'll see from the tips and tricks, processors can often be used as
effects in their own right, or as part of an effect chain, but until you
know exactly what you're doing and what the consequences are likely to
be, it is a good idea to stick to these guideline definitions, as they
dictate how you can connect the effects into your system.
If a device has a Mix control on it that goes from
100 percent wet (effect only) to 100 percent dry (clean only), then you
can be pretty sure it is an effect. If it doesn't have a Mix control,
and doesn't rely on electronic delays to create its results, then it is
probably safe to assume it is a processor.
Effects can be connected via insert points, or the
effect send and return loop that is included in most consoles and DAWs
(Digital Audio Workstations). When effects are used in the send/return
loop, their Mix control should be set to 100 percent wet, so you add
back only effected sound to the dry sound, which comes directly through
the mixer channel.
Processors, on the other hand, comprise an entirely
different water heating appliance filled with piscean vertebrates, as
they tend not to need any of the dry sound, other than in a few
specialist applications. As a rule, processors such as EQ and
compression are connected only via track, bus or master insert points —
at least until you have the necessary experience to understand why you
might want to break the rules once in a while. Having got that off my
chest, let's look at some specific effects (we'll look more closely at
processors another time).
Echo & Delay
Echo and delay are created by copying the original
signal in some way, then replaying it a short time later.
There's no
exact natural counterpart, though the strong reflections sometimes heard
in valleys or tunnels appear as reasonably distinct echoes. Early echo
units were based on tape loops, before analogue charge-coupled devices
eliminated the need for moving parts. Today, most delay units are
digital, but they often include controls to help them emulate the
characteristics of the early tape units, including distortion and
low-pass filtering in the delay path and pitch modulation to emulate the
wow and flutter of a well-used tape transport.
While pure digital delay produces perfect echoes, an
analogue emulation can be more musically useful, as each successive
echo becomes less distinct, creating a sense of distance and
perspective. Hi-fi echoes tend to confuse the original sound, while the
human hearing system seems better able to separate lo-fi echoes from the
original clean sound.
The feedback control regulates the number of echoes
by feeding some of the output back to the input. If you apply too much
feedback the delay unit will self-oscillate — an effect often used in
dub music. Delay normally relates to a setting with no feedback whereas
echo uses feedback to produce a series of diminishing repeats.
You don't have to use long, distinct delays: short
delays up to 120ms can be used to create vocal doubling effects,
normally set with little or no feedback. Nor do you have to dedicate a
delay to a single sound: you can configure it via an aux send so that
several tracks can be treated with different amounts of the same delay
or echo treatment, which not only saves on processing power (or buying
separate units!), but can help to make elements of your mix work better
together.
You can often use a tap-tempo or tempo sync facility
to get your echoes exactly in time with the song if that's the effect
you need, but many echo/delay plug-ins can be locked to your sequencer's
master tempo, enabling you to create precise, rhythmic delay effects.
|
Tips & Tricks: Panning
One special effect I used quite a lot in analogue
studios, but which is surprisingly tricky to implement in a lot of
software sequencers, is where you feed the left and right outputs of an
auto-pan effect to two different effects processors. With this setup,
the outputs of the two effects can then be mixed together to create a
variety of different modulation-style treatments. This patch always
worked well in a send-return loop with a pair of phasers, especially if
you also EQ'd the two returns wildly differently. The same setup used as
an insert could do great things with distortion and ring-modulation
processors, and if you were feeling really adventurous, you could fiddle
with the panning rate in real time while mixing down. Mike Senior
|
Reverb
I think it's fair to say that we all have a pretty
good idea of what reverb is, though there are several ways of emulating
it in the studio. Early reverb chambers, plates and springs have now
given way to digital solutions, which fall into two main camps:
synthetic and convolution. Synthetic reverbs take an algorithmic
approach, setting up multiple delays, filters and feedback paths to
create a dense reverberation effect similar to what you might hear in a
large room. Though these often sound a bit 'larger than life', they've
been used on so many hit records that we now tend to accept their sound
as being the 'correct' one for pop music production. Most can
approximate the sound of rooms, halls, plates and chambers, but in
comparison with a real reverberant environment, the early reflections
often seem to be too pronounced. The advantage of a synthetic reverb is
that the designer can give the user plenty of controls for altering the
apparent room size, brightness, decay time and so on.
In recent years, convolution reverbs have become
both affordable and commonplace. These differ from synthetic reverbs
insomuch as they work from impulse responses (or IRs), recorded in real
spaces to faithfully recreate the ambience at the microphone's position
when the IR was made. Sometimes these are referred to as sampling
reverbs but there's no sampling involved as such, even though the
process seems akin to sampling the sonic signature of a room, hall or
other space.
Because IRs can be recorded in virtually any space,
convolution reverbs generally come with a library of IRs ranging from
small live rooms to famous venues, top studio rooms, forests, canyons,
railway stations and just about anything else you can think of. They
sound very convincing, and there's plenty of variety to be had, but once
the IR is loaded, there's only a limited amount of editing you can do
without spoiling the natural sound. Usually you can apply EQ and also
change the envelope of the reverb decay to make it shorter, and adding
pre-delay is not a problem, but after that you pretty much have to take
what you get. Some companies, such as Waves, have managed to create
additional controls but, as a rule, the further you move from the
original IR, the less natural the end result.
Ironically, the sound of certain synthetic reverbs
is now such an established part of music history that most convolution
reverbs come with some IRs taken from existing hardware reverb units or
from old mechanical reverb plates. Also, if you have a convolution
reverb, it is worth checking the manufacturer's site, as additional IRs
are frequently available for download.
All serious reverb units have a stereo output to
emulate the way sound behaves in a real space and, in the case of
convolution models, the IRs are often recorded in stereo, using two
microphones. Some surround reverbs are also available.
Reverb creates a sense of space, but it also
increases the perception of distance. If you need something to appear at
the front of a mix, a short, bright reverb may be more appropriate than
a long, warm reverb, which will have the effect of pushing the sound
into the background. If you need to make the reverb sound 'bigger', a
pre-delay (a gap between the dry and wet signals) of up to 120ms can
help to do this without pushing the sound too far back, or obscuring it.
Though reverb increases the sense of stereo width,
it dilutes the sense of stereo position. If you want to pinpoint the
placement of something in a mix, you should consider using a mono rather
than a stereo reverb, and panning this to the same place as the dry
sound.
Most synthetic reverbs allow you to balance the
level of the early reflections and the later, more dense reverb tail. If
you want to keep the sense of space but without the reverb tail taking
up too much space in your mix, you can increase the early reflection
level and reduce the tail level.
As a rule, you don't add much, if any, reverb to
low-frequency sounds, such as bass guitar or kick drums. Where you need
to add reverb to these sources, short ambient space emulations usually
work better than big washy reverbs, which tend to make things sound
muddy. Taking this a step further, you can also make a mix sound less
congested by EQ'ing some low end out of your reverbs.
|
Tips & Tricks: Amp Modelling
One of the most useful features of guitar-amp
simulation plug-ins is that they can help mask some quite serious
problems with whatever you're putting through them, without necessarily
changing it beyond all recognition. I've found that even relatively
clean settings can disguise such horrors as clipping on transients to a
surprising extent. If you're ever faced with a badly recorded guitar
part (even one that's played on an acoustic guitar, or through an amp),
try putting it through an amp modeller.
As described elsewhere in this article, pitch-shifting can work well in
conjunction with amp simulation, but other ways of editing and
processing the raw guitar file before it goes through the amp modeller
also yield interesting results. Reverse reverb, resonation, vocoding and
Auto-Tune can all produce distinctive effects. Try chopping
small sections of guitar out, for an interesting stuttering effect
that's nothing like tremolo. A piece of guitar that's been reversed
before being fed through an amp modeller sounds quite different to what
you get by reversing a guitar part that's already been through an amp,
and this technique can be very effective. Likewise, recording three or
four separate tracks of single guitar notes and routing them
simultaneously through the same guitar amp simulator sounds very
different from playing chords. Sam Inglis
Re-amping a DI'd keyboard or bass can really liven
up a sound, but if you don't have access to a nice amp or amp modeller,
you can simulate the effect by sending the audio to a bus with a delay
plug-in set to a short delay time and with the wet signal set to 100
percent and dry to 0 percent. Then send the bus's output to another bus
with a distortion (or better still, a guitar amplifier emulator) plug-in
inserted. This simulates the delay you get from miking up a speaker,
and if you blend this in with the DI'd sound, it can give the recording a
live feel — especially if you use a convolution reverb to add some
'room' ambience. You may also want to roll off the very low and high
frequencies to help get rid of that DI'd vibe. Nicholas Rowland
|
Modulated Delays
Effects such as chorus, phasing, flanging and pitch
vibrato are created using pitch modulation and, except in the case of
vibrato, the modulated sound is added back to the original to create the
effect. The pitch modulation is generated by delaying the signal by
just a few milliseconds, and then modulating the delay time, using a low
frequency oscillator (or LFO). For vibrato, this is all that needs to
be done and, because the delay time is actually very short, the effect
is perceived as happening in real time. The other effects, however,
generally rely on an equal balance of the dry and modulated signals to
achieve the strongest effect, so it is easier when working with plug-ins
to adjust the wet/dry balance using the plug-in controls, rather than
adding the wet only signal via a send/return loop. As a rule, these
effects aren't very processor-intensive so, if you're working with
plug-ins, you can probably afford to insert as many as you need into
track or bus insert points as required. Stereo versions of these
plug-ins may generate different modulated delays for the left and right
channels to create a more dramatic spatial effect.
Chorus and flanging are created in fairly similar
ways, the main difference being that chorus doesn't use feedback from
the input to the output and generally employs slightly longer delay
times. Phasing is similar to both chorus and flanging, but uses much
shorter delay times. Feedback may be added to strengthen the swept
filter effect it creates. Phasing is far more subtle than flanging and
is often used on guitar parts. With chorus, phasing and flanging, the
delay time, modulation speed and modulation depth affect the character
of the effect very significantly. A generic modulated delay plug-in
allows you to create all these effects by simply altering the delay
time, feedback, modulation rate and modulation depth parameters. Most of
the time, low modulation depths tend to work well for faster LFO speeds
(often also referred to as the rate), while deeper modulation works
better at slower modulation rates.
Chorus is useful for 'softening' rhythm guitar or
synth pad sounds, but it does tend to push sounds further back into the
mix, so it should be used with care. Adding more brightness to the sound
can help compensate for this effect. Chorus also works well on fretless
bass, but tends to sound quite unnatural on vocals. Phasing can be used
in a similar way to chorus but, whereas chorus creates the impression
of two slightly detuned instruments playing the same part, phasing
sounds more like a single sound source being filtered, where the
frequencies being 'notched out' vary as the LFO sweeps through its
cycle.
Flanging is the strongest of the standard modulation
effects. The feedback control increases the depth of the 'comb
filtering' produced when a delayed signal is added back to itself.
Because it is such a distinctive effect, it is best used sparingly,
though it can also be used to process a reverb send to add a more subtle
complexity to the reverbed sound.
Though modulated delays are essentially effects, the
need to balance the dry and delayed sounds as a means of regulating the
effect strength means that using these devices via insert points makes
them much more controllable than trying to use them in an effects
send/return loop. If you do use them as a send effect, you can achieve
this balance by automating the send level.
|
Tips & Tricks: Dynamic Effect Modulation (MIDI Control)
One of my favourite hardware effect units is the
Electrix Mo-FX (sadly no longer in production). It is superbly
constructed for hands-on performance and it offers full MIDI control
over the panel's knobs and buttons. I use this in conjunction with the
Sequentix P3 (a hardware step sequencer). Not only can the P3 generate
patterns of controllers suitable for varying multiple Mo-FX parameters,
but it can generate evolving or shifting patterns, courtesy of its
'accumulators'. In a nutshell, accumulators are designed to prevent your
sequences becoming annoyingly repetitive: controller values (actually
values directed at any internal sequencer parameter) can be added or
subtracted on each pass of the pattern, with rules and limits directing
the behaviour as the accumulation progresses. Digging through the Mo-FX
manual quickly reveals all the MIDI Continuous Controllers you need.
Usefully, you can also trigger the tap-tempo function via MIDI, and this
offers a rather wonderful way of generating clock intervals. As you can
decide exactly where to place your tap-tempo trigger events, and the P3
sequencer can shift or vary these events according to rules you devise,
you can find clock sync intervals unseen on any other device. Paul Nagle
|
Pitch-shift
Pitch-shifters work by slicing the incoming audio
into extremely short sections (typically a few tens of milliseconds
long) and then lengthening each section where the pitch is to be
decreased, or shortening each section where the pitch is to be
increased. Though cross-fading algorithms and other techniques are used
to hide the splice points, most pitch-shifters tend to sound grainy or
warbly when used to create large amounts of shift (a couple of semitones
or more), though they can sound very natural when used to create subtle
detuning effects, using shifts of a few cents. A refinement of the
system, designed for use with monophonic sources, attempts to
synchronise the splicing process with whole numbers of cycles of the
input signal, which makes the whole thing sound a lot smoother but, as
soon as you present these devices with chords or other complex sounds,
the splices again become audible.
Though some sophisticated processors combine pitch
detection with pitch-shifting, to generate musically correct harmonies
in user-defined keys, simple pitch-shifters always change the pitch by
the same number of cents or semitones. In musical terms, that means that
only the octaves, parallel fourths and fifths are very useful. Other
intervals tend to sound discordant, as they don't follow the intervals
dictated by typical musical scales.
When using subtle detuning to thicken a sound, I
suggest trying values of between five and 10 cents and, where possible,
adding both positive and negative shifts, to keep the pitch centre
correct. Then combine with the dry sound and adjust the level to control
the subjective depth of the effect. This is very effective for
fattening up guitar solos or backing vocals.
By putting a pitch-shifter before a delay, then
feeding some of the output of the delay back to the input of the pitch
shifter, you can create delays that keep climbing or falling in pitch as
they recirculate. Though not always very useful in a musical context,
this effect is often used in TV and film dream sequences.
Because large pitch-shifts can sound grainy, it is
common to combine the effect with the dry signal, rather than using only
the 100 percent effected signal, though ultimately this is an artistic
rather than technical decision.
Though pitch-shifting is an effect, it is easier to
control when used via an insert point. However, if you need to use the
effect on several tracks in varying amounts, you can use it via a
send/return loop, providing the shifter is set to 100 percent wet. That
way, you can adjust the effects depth for individual mix channels by
using the send control feeding the pitch-shifter.
|
Tips & Tricks: Circuit Bending
There are an awful lot of boutique guitar effects
manufacturers out there who make pedals designed to create all kinds of
twisted and bizarre sounds. Sadly, their products are often very
expensive, often prohibitively so — so what about the more
budget-conscious would-be sonic terrorist? Well, one option is to
'circuit bend' more conventional (read 'cheaper') guitar effects. The
basic idea behind circuit bending is that you experiment with
short-circuiting the pedal until it makes a noise that you like, and
then solder in a connection, with a switch or potentiometer in place if
you think you may want to turn the noise off again at some point.
Guitar pedals are perfect for this. Firstly, and
perhaps most importantly, because you should never try to circuit bend
anything mains-powered, they can run off 9V batteries. Secondly, their
internal circuitry is usually very simple, and they already have audio
I/O. Thirdly, you can get them for almost no money from eBay, and the
other tools required — soldering iron, wire, switches, and so on — are
also very cheap. There's an almost infinite number of sonic
possibilities to be explored here, from finding new ways to process a
signal (of course you don't just have to use them with guitars) to
creating a machine that goes 'Eeeeeeooooowsquelch blipipipip' in a
different way every time you turn it on — and who would say no to that
for less than a tenner?
For more information and some examples of unintentional sonic mayhem, check out www.circuitbenders.co.uk and www.anti-theory.com/soundart/circuitbend.
Have fun. Rob Kemp
|
Tuning Correction
By contrast, tuning (or pitch) correction processors
and plug-ins are normally considered processors rather than effects,
but they do have creative uses. The idea behind these devices is to
monitor the pitch of the incoming signal, then compare it to a
user-defined scale, which can be a simple chromatic scale or any
combination of notes. Pitch-shifting techniques are then used to nudge
the audio to the nearest semitone in the user's scale but, because the
amount of pitch-shift required is usually quite small, the result
doesn't sound grainy or lumpy, as often happens when large amounts of
pitch-shift are generated. Because pitch tracking is used to identify
the original pitch, only monophonic signals can be treated.
When used with the human voice, it is important that
the pitch correction doesn't happen too quickly, otherwise all the
natural slurs and vibrato will be stripped out leaving you with a very
unnatural and robotic vocal sound. If only a few notes need fixing,
consider automating the pitch-corrector's correction speed parameter so
that it is normally too slow to have any significant effect, then
increase the speed just for the problem sections. This prevents
perfectly good audio from being processed unnecessarily.
If you stick to a simple chromatic scale (all the
semitones), you also run the risk of the pitch correction moving the
audio to the wrong note if the singer is more than half a semitone off
pitch. A user scale, containing only the desired notes, generally works
much better. Some systems also allow you to dictate the correct notes
via MIDI. If the song contains sections in different keys or that use
different scales, it is often simplest to split the vocal part across
several tracks and then use a different pitch-corrector on every track,
each one set to the appropriate scale for the section being processed.
If your audio track suffers from a lot of spill, or
includes chords, the pitch correction may not work correctly. Where
spill is loud enough to be audible, you'll hear this being modulated in
pitch alongside the wanted part of the audio as it is corrected. As a
rule, chords are ignored, so guitar solos, bowed stringed instruments
and bass parts (including fretless) can be processed, and only single
notes will be corrected.
The main creative application for pitch correction
is the so-called 'Cher effect', which is achieved by setting the
tracking speed as fast as possible to deliberately generate a
robotic-sounding result. It's a matter of taste, but for me, this is one
effect that has already been done to death!
|
Tips & Tricks: Delay
Tempo Delay: Most plug-in and hardware delays now
allow you to automatically sync delay times to MIDI clock and then
specify the interval of the repeats in terms of note values rather than
milliseconds. A trick here is to use two simultaneous tempo-based delays
with, say, a triplet delay setting, panned hard left, and a
straight-note delay panned hard right. Things can get more interesting
still if you apply this technique using ping-pong delays, so that
alternate repeats bounce from one side of the stereo spectrum to the
other. To create a true 3D effect, play around with the amount of
original signal left in the middle. Depending on the intervals between
your repeats, you can turn simple guitar and synth lines into complex,
arpeggiator-like patterns or totally spaced out ambient pieces. Stephen Bennett
Ostentatious Delays: If you're making very rhythmic
music of any kind, it makes sense to use tempo-sync'd delays, to avoid
undermining the main pulse. However, simple tempo-sync'ed delays tend to
be masked by the main rhythmic stresses, so they sink into the
background of the mix unless mixed very high in level, which makes it
difficult to create ostentatious delay effects in rhythmic music without
swamping your mix. One solution to this problem, very common in trance
music, is to set a delay to a three-16th-note duration, which means that
although the delay repeats never step outside the 16th-note grid,
they'll often miss the main beats and therefore remain clearly audible. Mike Senior
Keep It Reel: Perhaps because a humble tape echo
was the first effect I ever owned, delay has always been my primary
effect. Whether to liven up repetitive loops or add apparent complexity
to simple solos, it's worth getting to grips with delay the
old-fashioned way. This means daring to switch off MIDI sync and
manually setting delay time, driving feedback to the brink of madness,
or routing the pure delay output through equalisers, filters and so on.
Many of today's digital delays allow you to darken the delay iterations,
but there's no reason not to find your own method to achieve this:
adding alternative colours and discovering your own favourite processes.
I find precise, perfect digital delays can be rather generic and
characterless — so the more I delve into additional treatments, the more
interesting and organic the results are. Paul Nagle
Softer Delays: I'll usually have at least a couple
of delays as auxiliary effects in a rock or pop mix, but I often find
that bringing the general level of the delay as high as I want it makes
any transients stand out too much. When I'm sending single notes on a
clean electric guitar to a delay line, say, I tend to want to hear a
wash of sound, not the rhythmic 'CHA-Cha-cha-cha-cha' of a repeated note
attack. For this reason, I'll often put a gate or expander before a
delay, with an attack time set to 10ms or so. This is enough to 'chop
off' any abrupt transients, and makes the delay sound much smoother. Sam Inglis
Non-sync'd Delay: We are so used to perfectly
sync'd delays that it's easy to forget that manual sync and a pair of
ears has a charm all of its own. Even delay times that bear no obvious
relationship to the tempo can add dynamic movement and feel to a track:
check out some early King Tubby if you need reminding of this. Paul Nagle
Subtlety: You don't always have to make longer echo
or delay effects obvious in the mix for them to be effective. Once
you've set up the delay times and panned them to suit your song, try
dropping the delay levels until you scarcely notice them during most of
the mix (listening on headphones often helps set the most suitable
level). This generally results in intriguing little ripples of repeats
that you notice at the end of verses or during pauses, that add interest
and low-level detail to the mix. Martin Walker
|
Distortion
Technically, distortion is defined as being any
change to the original signal other than in level. However, we tend not
to think of processes such as EQ and compression as distortion, and the
term is more commonly used to describe processes that change the
waveform in some radical and often level-dependent way. These include
guitar overdrive, fuzz, and simply overdriving analogue circuitry or
tape to achieve 'warmth'. In the analogue domain, heavy overdrive
distortion is usually created by adding a lot of gain to the signal to
provoke deliberate overloading in a specific part of the circuit. Such
high levels of gain invariably bring up the level of hum and background
noise, so it may be helpful to gate the source. Though overdriving
analogue circuitry is the traditional way of creating intentional
distortion, we now have many digital simulations, as well as some new
and entirely digital sound-mangling algorithms.
The most musically satisfying types of distortion
tend to be progressive, where the audio waveform becomes more 'squashed'
as the level increases. Hard clipping, by contrast, tends to sound
harsh. All these types of distortion introduce additional harmonics into
the signal, but it is the level and proportion of the added harmonics
that creates the character of the sound. Harmonically related distortion
can be added at much higher levels than non-harmonically related
distortion before the human hearing system recognises it as such, so
there is no way to define a percentage of distortion below which audio
is acceptable or above which it is unacceptable. The reason that digital
distortion has its own character, which most people find less musically
pleasant, is because it is not usually harmonically related to the
input signal. For example, quantisation distortion, which results from
sampling at too low a bit depth, sounds quite ugly, though many dance
and industrial music producers have found a use for it, and some
plug-ins deliberately introduce it.
The use of overdrive distortion as a musical effect
probably originated with electric guitar amplifiers, where the less
pleasant upper harmonics created by overdriving the amp are filtered out
by the limited frequency response of the speaker. If you use a
distortion plug-in without following it up with low-pass filtering (or a
speaker simulator) in this way, you may hear a lot of raspy high-end
that isn't musically useful. This is why electric guitar DI'd via a fuzz
box or distortion pedal sounds thin and buzzy unless further processed
to remove these high frequencies.
The warmth associated with tube equipment and
analogue tape is quite subtle when compared with deliberate overdrive
effects. As a rule, if you're trying simply to warm up a sound and you
can hear the distortion, you should back off it a little, as there's
probably too much of it.
Adding a little distortion to sounds such as drums,
electronic organs, and even vocals, can help them stand out in a mix,
and give substance to a sound that's too thin or uneven. Software guitar
amp models often sound more convincing if you use external guitar
pedals to create overdrive prior to the audio interface.
Effects are fun, and can make mixing a more creative
process, but it's worth bearing in mind that they won't help in
situations where the basic principles of recording have been ignored!
Used with care, effects can help turn a good mix into a great one, but
they are seldom successful in covering up other problems. It is also
very easy to over-use them — sometimes their most valuable control is
the bypass button, and it is certainly worth learning to use the basic
effects well before throwing lots of complicated tricks at your sound.
As long as you let your ears decide what is right, you should be OK, and
a little critical listening to your favourite records will give you a
feel for what works and what doesn't.
No comments:
Post a Comment