Recording - May 2018 - 54

STUDIO 101

PART 5

Instruments-
Real and Virtual

n our discussion of the recording process, so far we've focused on only part of the sonic world: sounds that
are represented by air pressure waves, captured with microphones. Many modern musical styles feature
sounds that may have never existed as acoustic signals until they hit your monitor speakers. This month,
we'll cover recording electric and electronic instruments, making sure that we maximize their signal quality,
and look at some ways of enhancing their sound post-recording.
BY DARWIN GROSSE

But first, the Match Game
Before we talk about the instruments themselves, we need to
talk about signal levels and our need to create a match
between systems. When we talked about microphones, we talked
about them generating a very low-level signal, and the need to
use a preamp to increase the gain to "usable" line levels. But what
level is usable? The answer depends on the destination.
On consumer-level equipment, line level is labeled "-10 dBV",
which means that the maximum level is 10 dB below the reference
level of 0 dBV = 1 Volt (remember that decibels are meaningless
without a reference). On this scale, maximum volume level will
produce a peak at around 0.447 volts.
Professional recording equipment will
have a line level of "+4 dBu"-the
maximum signal voltage is 4 dB above
the 0 dBu = 0.775 V standard (which is
historically relevant for reasons we won't
cover here), giving a maximum volume
peak at 1.736 volts. It's common to use
the shorthand "-10 and +4."
In most cases, we can get a hint about
the expected level by the connector
that devices use: -10 gear tends to
use unbalanced (two-conductor)
RCA connections, while +4 gear often
uses balanced (three-conductor) XLR or
1
/4" connectors. The difference in level
is significant; it means that you need
to take notice when connecting devices that use different line
levels, so that the source doesn't overload the destination or
be too soft and noisy. These two standards inform us of a
standard voltage level that an amplifier needs to produce to
get a microphone, instrument or other equipment to be a
voltage-volume match.
Since we will be boosting lower-level signals, we'll need
an amplifier of some sort. Most amplifiers that take a signal
to line level are called "preamplifiers" to distinguish them
from speaker-driving power amplifiers. A mic preamp takes
the very low signal from a microphone and pushes it to line

level; an instrument preamp boosts a signal before it reaches
a power amp, while sometimes changing its tone.

Electric instruments
Electric instruments like guitars and basses use a pickup-a
long wire coiled around a magnet-to capture the vibration
of a metal string and turn it into an electrical signal. This can
cause problems for the engineer, especially if we decide to
record the direct sound of the instrument itself.
Electric instrument players are used to playing through
amplifiers, so most consider the sound of an amp to be a
critical part of their tone, and they may
find the sound of a direct connection
to an audio interface to be too sterile
sounding. Thus, even if you are directly
connecting the guitar to your recorder,
you will often want to simultaneously
mic and record an amplifier. This helps
the player feel more at home while giving
you more options during mixdown.
Bass players, on the other hand, don't
always demand a miked amp; the bass
is usually meant to be clean and focused,
so playing directly into a mixer or interface for recording is often preferable. A
bass preamp, when it's used, provides
tone control without the headaches of
miking an amp.
The main problem with direct recording of guitars is
mismatched impedance. Impedance, in very simple terms, is
how much a device hampers the flow of signal in or out. As a
general rule, you want the input impedance of your destination
to be much higher than the output impedance of your source.
Guitar pickups have a much higher output impedance than
mics, so you can't run long cables from them or plug them
into a mixer without your tone suffering. High-impedance
instrument-level signals need to be converted into low-impedance
mic-level signals, which is often done with an inline box called
a DI (direct inject) box. Some guitar amps have direct preamp

Even if you are directly
connecting the guitar
to your recorder, you
will often want to
simultaneously mic and
record an amplifier.

RECORDING May 2018

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