The architecture of a basic DSP system.. The very mention of
the word causes many guitarists
to wince, conjuring memories
of harsh, inspiration-crushing
tone from early rack gear and
floor-based multi-effectors. The
common misconception that
everything digital somehow
sounds cold and sterile isn’t
entirely unfounded. Back in
the early days of digital signal
processing (DSP), processing
power was extremely limited.
Early digital audio systems suffered
from low sample rates and
bit depths, poor dynamic range,
and harsh clipping characteristics.
The result was that many
digital effects designers were
forced to use creative tricks
and compromises to overcome
the limitations of their early
digital systems. Whether it was
a flanger, reverb, or distortion,
the tone was often less than
stellar compared to the vintage
effects we all knew and loved.
And so, over the years analog
gear and effects have gained a
fondness in our minds—a sort
of pre-digital innocence and
beauty. It’s analog, so it has to
be better right?
Let’s take a look at some of
the specs of early digital systems
and their impact on audio quality.
Due to a lack of sophisticated
integrated circuit (IC) chips,
the digital effects of the early
’80s were generally digital delay
line effects—that is, delay, chorus,
and flanging. These systems
implemented 12-bit converters
running at sample rates as low
as 15 kHz. In a digital system,
each bit of resolution will theoretically
give you about 6 dB
of dynamic range. So, a 12-bit
converter would be capable of
only 72 dB of dynamic range.
The highest frequency that can
be reproduced is half the sample
rate, so that would be 7.5 kHz
in a 15 kHz-sampled system.
These specs are so out of line
with current technology that
they have earned a place as “old
school” or “vintage digital.” If
you’ve ever played through a
bit-crusher pedal, you’ve experienced
the sound of low bit
depths and sample rates as a
special effect.
By the late ’80s, digital effects
had CD-player specs of 16
bits (yielding a 96 dB dynamic
range) and a sample rate of 44.1
kHz or 48 kHz. During the
same period, more advanced
digital IC chips became available,
allowing for implementation
of multi-effects, reverbs,
and nonlinear effects like digital
distortion and compression. This
new standard was still plagued
with shortcomings, as the audio
converter technology required
the use of sharp “brick wall” filters
that created non-linear phase
distortion at the top end of the
audio spectrum, resulting in
subjective “listener fatigue” and
“harshness.” Additionally, the
processing power was still very
limited for the ambitious applications
being pioneered. This
led to sonic compromises that
manifested themselves as harsh
clipping, metallic tonalities, and
fuzzy or fluttering note decays.
Fortunately, we’re at the
point now where we have a
massive amount of processing
power available and vastly better
analog-to-digital (A/D) and
digital-to-analog (D/A) converters
capable of well above 110
dB of dynamic range. Some
stompboxes now have more
processing power available than
early-’80s Cray supercomputers.
Simply being in a digital system
is no longer a limitation. On the
contrary, digital systems can do
things that simply aren’t possible
in 100-percent analog designs.
And effects that few studios
could have afforded only a
decade ago are now in the price
range of the humble musician.
I have to admit I get frustrated
seeing comments on
forums like, “It sounds digital.”
The truth now is that there are
no inherent sonic qualities to a
digital system. Digital effects,
for better or worse, sound
exactly how their designers have
built their hardware and algorithms.
If we think of a digital
system as a blank canvas, a DSP
engineer wields the brush, and
whatever algorithm he or she
writes ends up coloring your
guitar tone.
Let’s take a look at the
architecture of a basic DSP
system: The guitar signal
arrives at the input and is buffered
by some kind of analog
input circuitry. Then the signal
is sent to an A/D converter.
From that point, the signal is
represented by a binary stream
that can be easily processed.
Usually this is done by a DSP
circuit with some memory
connected to it. The DSP
circuit will run whatever algorithm
it’s been programmed
with and send the result to
a D/A converter, then to the
output jacks. Modern 24-bit,
192 kHz A/D and D/A converters
can provide excellent
signal-to-noise, THD (total
harmonic distortion), and
latency specs. Luckily, the
problems that plagued early
digital systems have become
mostly a non-issue with modern
converters and processors.
Digital effects are getting
better all the time. Some of
the digital gear currently on
the market brings us closer
to the old analog glory than
we’ve ever been before. And
some of it takes us to places
never before possible with
analog effects. Fear not—and
happy shredding!
Terry Burton
is an
engineer at—and the
founder of—Strymon.