RECORDING May 2022 - 46

Re-amp
In addition to varying amounts of channel outputs for monitoring
and such, many interfaces include a 1
/4
" re-amp out.
This output takes line-level signals from the DAW (like a direct
recorded dry guitar or bass) and converts it back to a Hi-Z instrument
impedance that can feed an amplifier or effects pedal
-hence the term re-amp.
INSIDE
THE BOX
with Joe Albano
INTERFACE BASICS
Microphones
Microphone inputs on an audio interface utilize a threeprong
female XLR connection. These will be connected to a
dedicated internal microphone preamp providing a suitable
input impedance and level. In most cases, the preamp quality
is proportional to the price of the interface.
Even the most spartan mic preamp equipped interface will
include a gain control and +48V phantom power (necessary
for condenser mics). There may also be a highpass/low-cut
filter (to eliminate thumps and rumbling), a phase/polarity
flip, an attenuation pad and more. Sometimes these are by
way of external controls, accessed through a software control
app or both.
Get in line
Line-level inputs are typically implemented as 1
/4
" jacks.
These are used for connecting mixing boards, keyboards,
drum machines, external signal processors, and multi-effects
guitar pedals.
But here's where you have to watch out-1
/4
" jacks are also
used to directly connect guitars, basses, and older analog and
mechanical keyboards. Despite using the same connector, line
and instrument inputs are not interchangeable.
Instrumental
An instrument input is designed to accept lower-level, high-impedance
signals from a (typically passive) electric guitar or
bass. The connection is usually labeled Hi-Z (Z is the electrical
symbol for impedance).
If an electric guitar/bass is plugged into a line-level input,
the signal will likely suffer from noise and tonal loss. Running a
line-level signal into an instrument input might overload too easily.
Most interfaces include both line-level and instrument inputs.
Sometimes they share the same 1
/4
equipped devices will combine all three into a single XLR 1
" jack. Many preamp/4
"
combo-style
input to save space. Often a button or switch is
employed to change from one function to another, and some
devices perform sophisticated self-switching.
46 RECORDING May 2022
Gain staging
Audio interfaces, big and small, will offer some physical controls
for setting the input (recording) and output (monitoring) levels.
There will be individual controls for each input in the best-case
scenario, with a master volume governing the overall output level.
The incoming signal should always be at a strong yet clean
level (well above the inevitable noise floor), but never so high
that it overloads the circuitry with clipping and distortion.
Most basic interfaces will offer a single LED per channel to indicate
signal presence and clipping (going into the red). Higher-end
devices often offer detailed, multi-stage input metering options.
Stereo multi-stage metering is also the most common for the
output signals.
Digital
The destination of all incoming analog signals in an audio
interface is the analog-to-digital (A/D) converter. This component
turns your analog audio into digital zeros and ones, ready to be
captured and processed in your DAW. Again the quality of the
conversion is usually determined by the price of the interface.
Clipping and overloading the signal in the A/D converter
is unlike the gentle overloaded analog " warmth " achieved by
pushing analog gear into the red. It's a harsh distortion (clicks/
pops/hash) that can ruin the recording. It's critical to make
sure that the overload indicators on the interface never go off
during recording, even if that means lowering the input gain
a little more than you'd like. As long as it's recorded cleanly
(in the DAW, always check the recording channel's meter), the
recorded signal can be adjusted in level later on in the computer.
Always remember, gain staging (maintaining the optimal,
clean signal level at every stage) starts at the interface.
Digital audio from your DAW is sent to your monitors and
headphones after passing through a digital to analog (D/A)
converter, usually of the same quality as the A/D.
RECORDING May 2022

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