Recording - July 2014 - 24

Reamping Secrets

Figure 3. The ProRMP by Radial Engineering is a reamp box that allows you to play back clean guitar from a recorder into
an amp with the full responsiveness and tone of the original performance. The signal is played through effects (if desired),
then into the amp, which is then miked and recorded.
have tons of flexibility later, for the tracking session you can just
point a good old Shure SM57 or Audix i5 at the amp, a few
inches away and somewhere between the center and edge of
the loudspeaker. That will sound fine for now, and you could
even record it along with the clean signal; the main reason to
have it now is so the guitarist hears something inspiring when
he or she plays.
On the other side of the DI you will find a 3-pin XLR output.
The signal on this output is a low impedance (150 Ohm) microphone level signal. You plug this signal into a mic input on a preamp, mixer, or interface, and record the direct guitar signal to
an audio track in your DAW. (See Figure 1.)
At this point you might decide that all this reamping business
is too complicated. Why not use any of the fantastic amplifier
simulation plug-ins on the market to cop your golden tone and
be done with it? You can certainly do that, with excellent results.
But you can still do better! The DI you plugged your guitar into
has an input impedance of its own, but how high? You probably want to make sure that your guitar "sees" the kind of input
impedance you would choose on a real amp so that your amp
simulator plug-in gets the same slightly loaded-down signal a
real amp would. So let's talk a bit more about DIs.
DIs were not invented for reamping. Rather they were invented so that bass and keyboards could be sent up the same snake
as all the mic signals and recorded direct, as these instruments
sound pretty good recorded direct... unlike a guitar, which really needs the warm coloration of an amp to sound good.
These early DIs had nothing inside them but a single transformer, a piece of iron in a square or round donut shape with two
separate coils of wire wrapped around it. (See Figure 2.) The wire
is coated with a thin layer of plastic so that electrical current cannot flow between the wire and the iron, or between adjacent turns
of a coil if they are wound close enough to touch each other.
If we connect an audio signal to one coil, it will generate a
magnetic field that will travel through the iron doughnut and
cause an identical signal to come out of the other coil. You could
connect a light bulb to the coil on the right and it would glow. In
this kind of circuit we would call the coil on the input the primary coil and the coil on the output the secondary coil. If the secondary coil has half the amount of wire as the primary, then the
signal coming out of the secondary will be half as loud as the signal going into the primary. This is how this type of DI converts
your guitar signal into a lower-voltage microphone level signal.
Because this type of DI needs no source of power to operate,
it is called a passive DI. Passive DIs generally have an input
24

RECORDING July 2014

impedance close to that of a guitar amp's lower impedance
input. The Radial Engineering ProDI is an excellent and affordable passive DI with an input impedance of 140,000 Ohms,
pretty close to the 136,000 Ohm impedance of the #2 input of
that Fender amp. Using this kind of DI will warm up the sound
of the direct signal you are sending to your amp sim plug-in.
What if you want to simulate the brighter #1 amp input? In this
case you might try an active DI. This type of DI requires a battery, a wall wart power supply, or the phantom power from your
microphone preamp or mixer to operate. Instead of a transformer, it uses transistors and other active electronics. The advantage of an active DI is that it can be designed to have any input
impedance desired. Some active DIs have a very high input
impedance, like the Countryman Type 85's 10,000,000 Ohms.
This DI will give you a brighter, crisper sound, which can be really great for bass guitar when you want a very tight, edgy sound.
Check out the specifications of any DI you plan to buy, as some
active DIs, like the dbx db12, have a lower input impedance
(140,000 Ohms in this case), and may sound more like a passive
DI. And this is especially true of the "Hi-Z" guitar inputs found on
many DAW interfaces nowadays... there is no official definition of
"Hi-Z", so you'll want to make sure your interface has a 1,000,000

Figure 4. These Hotone effects are set up to process a
reamped guitar signal being sent to this vintage Gibson
amp, where the resulting sound is miked and recorded.

Recording - July 2014

Table of Contents for the Digital Edition of Recording - July 2014