F ROMTHELA B
Dissecting Distortion Pt. 3
In last month’s column, we looked at images
of sound waves with and without distortion.
I’d like to examine those photos again for
some more analysis.
In Figures 1 and 2 we can see that the waveforms have about the same amplitude (
vertical height when viewed on an oscilloscope).
Amplitude corresponds to the size of the
signal in volts or electrical strength, thus the
bigger the waveform the louder the signal.
This is a general rule and there are always
exceptions – test equipment can be set to
see things in many different ways. However,
for this discussion,
remember that a bigger wave represents a
In Figure 1 we have a
nice, round sine wave.
This represents a clean
signal with no distortion. Figure 2 shows
a square wave and Figure 1
believe me, it is nasty
sounding. In the lab,
we “look” at audio
gear with a square
wave running through
it. A square wave,
although not pleasing to the ears, can
visually represent how
a particular piece of
gear is performing; in
this case, the squarer
the wave is, the better
the gear is passing the signal without altering it. For applications requiring pristine
audio, the wave should be very sharp and
uniform. Introduce EQ, filtering, overdrive
or distortion and the wave begins to take
on non-linear shapes.
A particular piece of gear or its components
all have a limit on how much signal, voltage
and amperage that they can handle accurately. After a certain point, distortion begins
to occur. If we were to add to the signal level
in Figure 1, there would come a point that
the gear could no longer handle the increase
and the sine wave would begin to flatten
and take on the appearance of the square
wave in Figure 2. In this case we would be
overdriving the limits of the particular piece
of equipment or the component’s ability to
cleanly pass the signal, thus the term “
overdrive.” Overdrive is the easiest way to cause
Looking at Figures 3 and 4 we can see how
a pedal affects the signal. Milder distortion
is shown in Figure 3 and total annihilation of
the signal is shown in Figure 4. In Figure 4
we see total compression of the waveform;
the amplitude is diminished as compared
to the wave in Figure 1. Although the wave
is smashed down, it is very rich in harmonic
frequency content and can sound as loud as
the sine wave in Figure 1. Figure 4’s wave
shows the same fundamental frequency
as in Figure 1, except with about a zillion
harmonic derivatives induced by the pedal’s
circuitry. While amplitude is relative to loudness, so is the complexity and harmonic
content of a signal.
Distortion and overdrive pedals basically
derive their sounds by two types of processing. The first and easiest way is to increase
the gain (amplitude) of the signal. The
second way is to change the shape of the
original signal by adding, subtracting, filtering, etc. We can use transistor gain staging,
diode clipping, harmonic regeneration/feed-back, opto circuit manipulation and many
other exotic circuit derivatives to cause
distortion. However, it should be noted that
both methods come with a price; overdrive
or distortion obtained by a function of gain
usually has a corresponding increase in
noise, while circuit manipulation of a signal
is often described as “tone sucking” and
alters the original sound of the signal.
Great examples of this are FET transistor-
based pedals (the typical “Tube Screamer”
type of pedal). FETs are an easy and inexpen-
sive way to obtain gain, but they get noisy
as the gain increases.
They also produce a loss
of low-end frequency
response, mid frequency
peaking and harshness
in the upper frequencies.
The gain increase and mid
boost is killer for push-
ing a 100-watt amp into
orbit for a solo, but the
loss of low-end response
and increased noise is
not acceptable for bass
players. Note: Many Tube
have IC chips as their
major component (in particular the beloved 4558),
but the chips are based
on FET technology.
And always remember
the basic premise of
overdrive and distortion:
when you are practicing
by yourself soak it up to
the top, but cut it way back when you get
with the band.
Come see us at the Orlando, Nashville,
Spartanburg, Dallas, and Summer NAMM
shows where the boys and I can give you an
earful. We enjoy teaching, ‘cause rock n’ roll
ain’t noise pollution (most of the time)!
Gary “Sarge” Gistinger
President, Creation Audio Labs, Inc.