Block diagram of
a flanger pedal.
LFO curves: With a low
width setting, the manual
knob determines the
filter/pitch nature of the
flange effect. With a high
width setting, the width
sweeps through filter and
pitch effects, and the
manual setting has only
a small influence.
As sonic chameleons, flangers can create
lush chorus sounds, airy harmonic textures,
moody frequency swirls, sweeping jet-airplane
swooshes, seasick pitch warbles, or
sci-fi ray-gun blasts. However, if you don’t
have an understanding of what the pedal is
actually doing, this tweakability can lead to
frustration when you try to dial in a particular
sound. Let’s take a look at the basics
and break down some of the mystery.
First, a little history. The flanging effect
originated from a studio trick involving two
synchronized tape reels playing identical
source material. The second reel was forced
out of sync by applying pressure to the tape-guide
“flange,” creating a varying delay relative
to the unmolested first reel. When the two
signals were combined, it produced a dramatic
and chaotic sweeping effect. The introduction
of bucket-brigade-delay (BBD) chips in the
’70s opened the door to capture this same
effect in a stompbox, with the BBD chip taking
the place of the “flanged” tape machine.
A low-frequency oscillator (LFO) replicates
the varying delay time of the flanged
deck. A typical flanger pedal has four
knobs, and three of them—speed (or rate),
width (range or depth), and manual—are
related to the LFO (see the flanger pedal
block diagram at right).
So what’s up with the fourth knob? The
regen (intensity or enhance) knob feeds some
of the delay output back into the input. This
control may have originally been added to
compensate for the fact that the studio tape
flanger trick could produce some extreme
sounds by speeding up the flanged deck ahead
of the original signal (creating what’s sometimes
called a “negative delay”), and then slowing
it down to pass through zero delay time,
whereas the pedal can only delay the signal by
positive amounts. The regen knob doesn’t produce
this particular sound, but it intensifies the
flanging effect and adds a bunch of sonic possibilities.
Later pedals obtained the “through-zero”
effect of actual tape reels by adding a
short delay in line with the input signal, but
we’ll save that for another discussion.
The typical delay range of a flanger is
about 0.5–10 ms. These delay times are
heard as filter effects at the shorter end of the
range (because frequency rises as delay times
get shorter), and pitch effects (chorusing) at
the longer times when combined with the
input signal. This is the nature of comb filtering,
which is what happens when a delayed
version of a signal is added to itself. The three
LFO controls determine how fast (speed),
how much (width), and in what delay region
(manual) the modulation occurs.
From a technical standpoint, the width
knob sets the LFO amplitude, and the
manual knob sets the LFO offset. Note that,
as the width is increased, the manual control
becomes less effective. When the width is at
maximum, then the entire region of delay
times is being used, so the manual control
doesn’t do anything. At the other extreme—
with width at zero—there is no oscillation,
just a fixed delay time that is adjusted by
the manual control, which allows a physical
sweep of the entire delay range.
With this information in mind, we can
formulate some general ideas about how to
craft particular sounds. Below are some starting
points to help you explore the diverse
sounds that a flanger is capable of. To add
more variables into the mix, the LFO sweep
shapes can be linear or logarithmic, depending
on the flanger—and some flangers allow
polarity changes on the feedback. Luckily,
the same basic principles still apply.
Chorus-like sounds: A chorus doesn’t
have any regeneration, so set the regen to
minimum. Set manual to its lowest setting
for long delay times. Keep the width low,
but not at minimum. (Remember, if the
width is at minimum, the LFO is not oscillating—hence, there will be no modulation
sounds.) If the effect is too pitchy, try
reducing the width or the speed.
Jet flyby: Set a moderate speed. Turn the
manual to halfway and crank up regen. Set
width to the desired sweep range, then adjust
manual to dial in the sweep region to taste.
Auto-wah: Set a reasonably fast speed
and keep width low to stay in a limited
region of delay times. Add some regen to
enhance the filter resonance. Then, experiment
with the manual control to tune the
Classic flanger sweep: A moderate speed
with maximum width allows the delay line
to sweep from the lowest to highest delay
times, thus showcasing the underlying character
of the flanger. Add some regen to taste.
Resonant filter: Set width to zero to
“freeze” the LFO. Add a generous amount of
regen to increase the resonance, and turn the
manual knob to dial in the filter frequency.
Freq out: Set all controls to maximum.
(As we mentioned earlier, with width at
maximum, the position of the manual
control is irrelevant.)
With this knowledge and a little practice,
you should now be able to use your
flanger to dial in a lot of different sounds
with authority. And don’t forget the value
of experimenting—turn knobs, play guitar,
and have fun!
is the DSP Engineer