Recording - March 2018 - 58

STUDIO 101

PART 3

Signal Flow In
The Studio

n the previous two articles in this series, we learned about the nature of sound, how it gets converted into electrical
signals, and how it gets digitized into content that can be used by the computer. We now have all the background
knowledge necessary to move into the studio. In this article, we are going to be talking about signal flow: how these

electrical signals and digitized bits move throughout the studio.
Common wisdom might have you thinking that there isn't much involved in using audio in a computer-based DAW: you
pour audio into an input jack on the computer and you have a recording, you pour it out of a different jack and have the
results. While this view might be built upon a kernel of truth, it helps to understand how the signals move from the source
to the endpoint, and what kinds of hardware are available to help you get the job done-or at least make it easier.
BY DARWIN GROSSE

Microphones and preamps
Let's start by talking about the signal path that most professional engineers are most obsessed with: the input chain. This is the
signal flow from the audio source (a singer, drummer or other performer) to the computer. There are three primary ways that information gets into your DAW: from a microphone, from an electric/
electronic instrument, or from a MIDI controller. We'll begin by
looking at the input chain used for recording acoustic sounds.
As we saw in Part 1, microphones are the tools used to
convert sound pressure waves into electrical signals. There
are many varieties of microphone-enough to justify a dedicated
article on the subject-but in all cases, the signal produced
by a microphone is very weak. To make that signal usable by
most other equipment, we need to greatly amplify it using a
device called a microphone preamp. Preamps take a low-level
signal and boost it to a common (higher) level that is more
conducive to low-noise, high-efficiency processing.
Preamps come in many varieties, and most engineers have
their personal favorites. You will find that some people are
dedicated to ultra-clean and detailed solid-state preamplifiers,
while others prefer the coloring that comes from tube-based,
transformer-loaded amplifiers. Establishing these preferences
comes through experience, but high-quality mic preamps are
part of almost every serious engineer's toolkit.

Compressors and EQs
Computer-based DAWs provide us with a lot of flexibility for processing, but there are some audio processes that
are sometimes best handled before audio ever gets into our
computer. Two of these are adjustments to frequency content
and dynamic range. The tool for frequency adjustment is
the equalizer (or EQ). EQ adjustments allow you to select
a frequency and either boost or reduce its level; this is the
equivalent of a tone control on a consumer audio device, but
a studio EQ is normally a lot more surgical, offering frequency
selection and a broader range of adjustment than a stereo
system might provide.
58

RECORDING March 2018

Dynamics control, which is managing the difference between
the loudest and quietest levels in your signal, is done by a tool
called a compressor. A compressor lets you choose a volume level;
when the volume exceeds that amount, the device starts automatically reducing the level. The result is that you can tame loud
sections of the sound, and keep the overall levels under control.
Managing levels is critical in front of the digital conversion:
digital inputs simply can not handle overly loud signals. Once
a signal hits the maximum input level, the digital bits are
stacked as high as they can be stacked-this is called full
code. (If you think of a 'word' of audio data as a bunch of 0
and 1 bits, full code is all 1s.) This is the maximum level that
can be stored and reproduced, so higher volumes will result
in a particularly harsh form of distortion.

ADC and converters
The tool that does our digitizing is the audio interface, but
technically, this represents a pair of devices: an analog-to-digital
converter (abbreviated A/D or ADC) and a digital-to-analog
converter (abbreviated D/A or DAC). The ADC moves data
from the analog domain (an electrical audio signal) into your
computer (bits), and the DAC turns the bits back into an audio
signal. In most cases, there aren't many options involved in
selecting an interface: the most important practical decision
is choosing the number of inputs and outputs you need. Basic
interfaces will have one or two input channels of A/D
conversion and two output channels of D/A, while larger
interfaces can have 16 or more of each.
When you are choosing an audio interface, you need to
think of inputs as the number of simultaneous discrete signals
you will want to record at once. If you are just recording your
guitar and voice, or a drum machine, you will probably be
able to get away with a 2-input interface. On the other hand,
if you expect to record an entire band with multiple drum
mics, you may need 16 or 24 input channels.
Output channel selection is a little more complicated. Most
times, we will only need to mix to a stereo pair of outputs.

Table of Contents for the Digital Edition of Recording - March 2018