Recording - November 2017 - 48

Understanding the

AUDIO SIGNAL PATH
Part 1 : Basic concepts _ By Bill Stunt
Simply put, the signal path is the route audio
takes from its source to a recording medium
or monitoring device. That simple description
belies a rather complicated and sometimes
fraught process. Even in the simplest of
signal paths-say, a direct to hard disk
recording-the audio must pass through at
least one amplifier and A/D converter. Using a
mixer or external preamplifiers adds complexity
to the route.
To mix that audio with other tracks requires a
complicated mixing device or DSP engine that
sums the individual tracks through a matrix of
channels, sends, buses, etc., to a master output. Every juncture along that path requires
the audio to pass through a number of circuits
or DSP processes. These need to interact with
each other near optimally in order to maintain
the integrity of the sound.

ONE EXAMPLE
In my home studio, I run signals to preamps, then into an interface and DAW as well as to monitors, sometimes with outboard
compression. Let's see what that "simple setup" really entails!
Microphones, DIs and instruments go into outboard preamps
(some with EQ and compression). Preamp outputs go to my
audio interface, which convert the analog signals to digital,
while splitting off analog audio to an amplifier for monitoring.
The digitized audio goes to my computer, where it is routed
through a Digital Audio Workstation. Those inputs are sometimes processed by DSP plug-ins as they are being recorded; I
use this to emulate analog workflow and "flavor".
Once recorded to disk, audio is routed through the DAW's
mix matrix. Within that matrix, I can create volume and pan
48

RECORDING November 2017

faders, inserts and sends, buses, FX channels, VCA channels,
multiple monitor mixes, and a Master output. I often use an
analog DAW output to an outboard compressor and return it
via an interface input; sometimes a hardware compressor can
add that certain thing I'm looking for during mixdown.
The mixed and processed audio passes from the DAW's
master output through the audio interface's D/A, then to an
analog output to an amplifier connected to my studio monitors
and headphones.
As you can see from Figure 1 (from PreSonus, maker
of Studio One, my primary composing DAW), there are
many junctures along the path, and all have the potential
to have a positive or negative effect on the quality of the
recorded sound.

NO SCHOOL LIKE THE OLD SCHOOL
Old school engineers were well versed in this by necessity-
mastery over all elements of the signal path was essential to quiet
and clean recordings. Some components in the signal path could
be quirky, to say nothing of magnetic tape's idiosyncracies!
Today's modern DAWs do a good job of managing signal
path somewhat transparently. DAWs and 24-bit audio files
have greater potential headroom than is attainable in an analog
system. That said, it is still very important to understand and,
at times, tweak signal path to get the best results. When
incorporating analog tools in digital tracking and mixing, some
old school smarts-understanding what happens to audio
passing through various elements of your rig-will help you
integrate those elements into your workflow effectively.
Early in my career, I was hired as an audio assistant at a
broadcast production company, working in a mobile unit. I
was lucky to have a head audio guy, Bill Baker, who took a
strong interest in teaching me about signal flow... the hard
way. During my very first week on the job, he gave me three
days to come up with a patch list, from stage to console to
analog multitrack, for a large production featuring multiple
music acts accompanied by an orchestra.
I spent a good part of that weekend trying to figure out
how to read a mixer's functional diagram, but the payoff was
well worth it. I managed to come up with a plan (and the
beginnings of a sophisticated understanding of signal path)

Table of Contents for the Digital Edition of Recording - November 2017