Recording - June 2016 - 10

Signals in a DAW? Yup! A signal isn't only voltage, it's a generic term
describing the flow of information between two points. It's voltage inside a
mixing console, but our signal path begins with air pressure on a microphone diaphragm, and ends up as air pressure emerging from a loudspeaker. Smoke signals are puffs of smoke, semaphore signals are flag
waves, and so on. Regardless of their form, to be of any use, signals must
somehow get from a sender to a receiver. That's "signal flow."
When I entered the world of computer audio after using a hardware
recorder and mixing console for nearly fifty years, what I saw on the
screen didn't make a lot of sense. It wasn't until I started thinking about
signal flow that the light bulb went on and I was able to make sense of
the virtual control room setup. Twenty years later, I'm still learning how to
do things in the DAW way, and when I get stuck, thinking about where
the signal needs to go next usually gets me over the hump.
Many people began recording with a computer and have never
worked with traditional studio hardware. Why learn about recorders and
consoles when you're using a computer? I've found that people grasp a
DAW concept more quickly and thoroughly when first thinking about its
hardware implementation. Signal flow is more intuitive when you can see
cables connecting outputs to inputs, or at least see them represented on a
wiring diagram. Furthermore, hardware is what it is-the knob, button, or
jack you see won't disappear or change with a mouse click.

DAW implementations of a given function, the signal flow is
very much the same for both. If you understand one, the other
will quickly become clear.
The process
A mixing console is generally considered to be the heart of
a multitrack recording system. It has a place for our microphone signal to go in, and another place for it to go out to
loudspeakers or headphones. It can also feed a recorder, and
the recorder playback can make its way to the speakers. A
DAW emulates all of these mixing, recording, and most importantly, signal routing functions.
Two things distinguish a multitrack recording console from
your band's PA mixer. First, it takes its inputs from both live
sources and from recorded tracks. Second, it must be able to
mix previously recorded tracks with the live source for monitoring while overdubbing. Figure 1 shows the signal flow when
recording with an analog mixer.
The recorder's track input usually comes from a console
channel's direct output, though it could come from a bus (more
later) within the mixer when, for example, using two mics on a
guitar amplifier and recording them together on a single track.

By Mike Rivers

Signal Flow in a DAW
Old-school thinking can yield great results when working "in the box"
1

While most DAW users understand how to apply EQ, compression, or
effects to a track, many find that satisfactorily monitoring what you're playing isn't so intuitive. Using this task as an example, we'll follow a working
signal path through traditional analog hardware, and then look at its
DAW equivalent.
Even in the simplest implementation, with only one signal path from mic
to loudspeaker, the signal must pass through every block in the chain to
get there. Full-featured interfaces offer more flexibility with more paths for
confusion. Though the names of the blocks differ between the analog and
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RECORDING JUNE 2016

(That was important when you had a fixed number of tape
tracks, but even with DAWs' infinite track count, some engineers like to get the sound they want, record it, and move on.)
In the DAW world (Figure 2), the job's the same, but the
blocks doing the work have different names and the tasks are
split up differently. A digital system first converts the incoming
analog voltage to a string of bits. Only after the analog-to-digital (A/D) converter has done its work, can the computer then
do the math of summing inputs, adjusting levels, and tweaking
the sounds. Finally, the digital-to-analog (D/A) converter converts the processed data stream back to an analog voltage to
feed the monitor system. Along the way, the digital audio
stream is stored on disk through a data path equivalent to the
analog mixer's direct output connected to the recorder's input.
Electricity travels at nearly the speed of light, so with an
analog signal path, output is essentially simultaneous with the
input. In the digital path, each block requires processing time,
so each block's output is delayed somewhat from its input. The
total delay is called latency, which contributes a unique set of
problems to a digital audio system. With modern hardware,
latency is just a few milliseconds, but it can still be annoying.
Hearing what you need to hear
One way to reduce monitor latency is to put a mixer inside
the interface box, catching the mic signal before it hits the
computer. The simplest approach is to use a simple analog
mixer with inputs from the live sources and a stereo mix of previously recorded tracks that you set up using the DAW's mixer.
More fully-featured interfaces use a high-speed digital signal
processing (DSP) chip and firmware to mix the A/D converter
output and DAW mix digitally. Because the path from source
to headphones bypasses the computer, latency can be as low
as a few tenths of a millisecond, which is rarely distracting.
Figure 3 illustrates the signal flow in an interface with an
analog monitor mixing path. The source is split (shown here
only for the top input) to feed both the A/D converter and the
monitor mixer, directly corresponding to the input monitor path
in the analog console of Figure 1. The mix of the recorded

Table of Contents for the Digital Edition of Recording - June 2016