Hi.
I'm Jon San Paolo here in Studio A of Electrical Audio, and today I'd like to give you
a couple of ideas for how to use a passive DI.
[clunk, clunk.]
So, quickly, I wanna tell you the differences between an active and a passive DI.
In the case of an active DI, we have an instrument-level signal that goes through either a vacuum tube
or transistor on its way out to a mic-level output.
You need phantom power in order for this to work for transistor-based and some sort of
external power for tube-based. And the signal will only flow in one direction.
On the other hand, with the passive DI, we use a transformer as the mechanism to convert
a high-impedance, instrument-level signal into a low-impedance, mic-level signal.
Because it's a transformer, we don't need to apply any sort of external power to it,
and by nature of it being a transformer, the signal can actually flow in either direction,
which is very, very helpful for us in the studio.
More on that in a minute...
So the most typical setup is what we have right here, where we wanna grab literally
the direct signal of any given instrument: guitar, bass, drum machine, synthesizer.
Pretty much every DI is going to have either a "PAD" or a "LINE/INSTRUMENT" toggle, so
just make sure it's set in the right spot.
And they're either going to have a parallel or a "THRU" jack, so just make sure that's
connected correctly.
Right now, we've got the bass guitar going into the DI, across the transformer,
and into the control room, and I also wanna grab the amplified signal, so I'm gonna plug IT in,
[amplified bass guitar drowns out speech] and now we have everything.
Hey! Re-amping!
This is when you have a line-level recording of a direct signal that you'd like to re-record
through an amplifier at instrument-level.
Essentially, we're running the signal here in reverse.
There are several purpose-built boxes made for re-amping, but you can also accomplish
this with a passive DI.
So, here we have a bass guitar loop going through the computer, into the console through
the fader, and from the "DIRECT OUT" of the console into one of the microphone tie-lines
in Center Field, and the idea of having that fader is so that send it out at a signal that's
not too quiet that it's making the amp hissier than it needs to be, but not too loud,
so that we're not overloading the amplifier as we go.
If you don't wanna use an analog console, or if you don't have one and you just wanna
use the DAW's output faders, you can do that.
So, here's the signal, right here, coming into this microphone tie-line.
It goes along the cable, into the direct box, transforming it from a line-level, low-impedance
source to an instrument-level, high-impedance source, that we can now
[bass guitar loop swells in volume]
feed into the amplifier and record as if it were a live instrument.
Say you have a musician who would rather be in the control room with you while he's tracking.
Taylor: "Yeah, this tone just kind of sucks."
A guitar output, or other unbalanced signal, is subject to signal degradation in runs longer
than about 20 feet. Not long enough to make it 2 or 3 rooms away, where your amp is.
A balanced, low-impedance signal, on the other hand, can be run up to hundreds of yards before
you'd encounter that risk.
The low impedance and balancing of a signal, like a mic-level signal, is what preserves
the signal quality over a long run.
So, if we take our high-impedance, instrument-level signal here,
we'll be able to convert it to a low-impedance, balanced signal, meaning that we can maintain
that signal integrity.
But, we're going to have to convert it back at the end of the line, so we're going to
hook a up another DI
here. Because we're using identical DI's, we're
doing essentially the reverse of what happened in the control room. So this signal is now
being converted back to a high-impedance, instrument-level signal, and therefore
the amp sees a high-impedance, instrument-level signal.
You can also use a series of DI boxes as a means of getting an effects loop in place
for vocals.
The first DI converts the mic-level signal into instrument-level and high-impedance,
which the pedals expect to see.
The signal goes through the pedal chain, then back into the second DI to covert it back
to low-impedance, and balanced mic-level.
Because transformers block DC, and thus can't transmit phantom power, you'll need to use
the output of the mic preamp if you're going to use a condenser mic, or an active ribbon mic.
Otherwise, you can go straight into the DI.
Here we have a 15" speaker cabinet. We really like to use this when recording drums because
it does such a great job of picking up the really low frequencies on a bass drum.
I'll show you how.
So what we do, is we butt the two of these together, and any time the bass drum is struck,
the speaker will vibrate sympathetically along with it.
So, we wanna take that small electronic signal that it produces and send it to the DI.
Once it goes through the DI, it'll go through into the control room, and then we can treat
it like any other microphone we have on the drum kit.
Here are some samples of recordings with and without that cabinet in the mix.
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