Recording - July 2014 - 23

So it is with an electric guitar output. Impedance is measured
in Ohms. A typical electric guitar has an output impedance of
about 33,000 Ohms, which is pretty high. To give you a comparison, the impedance of the main outputs on your USB audio
interface is only about 50 Ohms, and the output impedance of
a microphone is usually about 150 Ohms.
On a guitar amplifier like the Fender Deluxe Reverb there are two
inputs, labeled 1 and 2, on each of the 2 channels. The #1 inputs
have a very high input impedance of 1,000,000 (1 million) Ohms,
or about 30 times the output impedance of your guitar. Plugging
into this input gives you the loudest, brightest sound because it is like
that spray nozzle. The #2 inputs have a lower input impedance of
136,000 Ohms, only about 4 times the output impedance of the
guitar. Plugging into this input makes it harder for the pickup to keep
the pressure up, and the result will be a slightly quieter and noticeably warmer sound, which can be very, very lovely.
Guitars with high-output humbucker pickups sometimes work
better in the #2 input when you are going for clean sounds, and
better in the #1 input when extreme distortion is your dark god.
Guitarists and engineers frequently try all inputs on an amplifier
to find the one that has the type of sound they are looking for, and
it is all based on the ratio of the output vs. input impedance.
So, going back to your USB interface, connecting its 50 Ohm
output impedance to your amp will give you a nice, bright
sound, but not that magic, soft warmth that results from the 1 to
4 ratio between your 33,000 Ohm pickup and the 136,000
Ohm input. The USB interface might even sound a bit too bright
and cold connected to the 1,000,000 Ohm input. So we need
a way to connect the guitar into the proper input impedance,
record it dry, and then get the proper output impedance as we
connect it to an amp. This way it will sound just as it does when
you plug directly into your amp.

Figure 2. A typical transformer. Current in the primary coil
(on the left) creates a magnetic field that in turn induces
current in the secondary coil (on the right).
Going direct
There are two ways to do this, and we will start with the oldschool way from back in the analog tape days, before it was
even called "reamping", and then look at reamping itself. But
whichever way we use to get our recorded clean guitar signal
out of our DAW and back to the amp, we first have to get it in...
and to do that we need a DI (Direct Injection) or "direct box".
A DI has a 1/4" input and a 1/4" parallel output. The guitar is
plugged into the 1/4" input. You connect the direct output to your
amp and mic it as you normally would. Between the DI input
and the parallel output is nothing but wire, so the amp receives
the exact same signal it normally would. Since we are going to

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Recording - July 2014

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