Direct Results

Dec 1, 2006 12:00 PM, By Mike Levine

Few would dispute that the ultimate electric guitar tones are recorded from miked-up tube amps. That is, if you have a nice amp you can crank up, a good-sounding recording space (if you're using room mics), and time to experiment. But what if you don't? Or what if you have limitations on volume in your studio, don't want the amp sound to leak into other mics, or don't want to decide on the final guitar sound until mixdown? In those cases, direct recording may be the best alternative.

In recent years, amp- and cabinet-simulating modeling processors and plug-ins have made the task of getting a realistic tone from a DI (direct injection) — recorded guitar much easier. Those products let you process your guitar signal (during either tracking or mixdown) with amp, preamp, cabinet, and effects emulations. Plug-ins like Native Instruments Guitar Rig 2 (see Fig. 1), IK Multimedia's AmpliTube 2 (see Web Clip 1), and Waves GTR 2.0 (reviewed in this issue) not only give you a large selection of amp, cabinet, and effects models, they also let you specify the routing of your virtual components. Even though modeling devices and plug-ins may not be able to precisely match the sound of a boutique or vintage tube amp, they offer a much wider range of tones.

DI IQ

At its most basic, a DI setup contains a guitar patched into a digital audio sequencer or a multitrack through a high-impedance guitar input in an audio interface or a mic preamp, possibly with the signal first going through a direct box. In order to accurately capture the tone of your pickups, it's important to use an input with an impedance that's optimized for guitar. Guitar inputs on many preamps, audio interfaces, and DI boxes have a 1 MΩ input impedance, which is the same value found on the inputs of classic tube amps from companies like Vox, Fender, and Marshall. If your input device has an impedance substantially below 1 MΩ, you may notice a rolling off of high end. Impedances above 1 MΩ can yield a brighter, more sparkly tone.

If your audio interface doesn't have a dedicated instrument input, you'll probably want to use a direct box. If you're recording through a mixer, a direct box is usually the best way to go too. A direct box converts your high-impedance, unbalanced guitar signal into a low-impedance, balanced signal that's output on an XLR connector and can be patched into one of the mic preamps on the mixer or audio interface. (Most of the time you'll want to go through a mic preamp, but some DI boxes, such as Groove Tubes' Ditto Box, provide sufficient gain to patch into a line input.) It also outputs the signal through a ¼-inch pass-through jack for connection to an amp or guitar processor if desired. On some direct boxes, this output is buffered, which allows for longer cable runs without signal loss.

On any direct box, the main XLR, low-impedance output gives you the ability to send your signal unaffected through long cable runs, such as in a studio with tie lines. The main output is also balanced, which can help prevent noise on the line.

DI boxes come in two basic flavors. Active direct boxes contain active electronics, including a buffer amp that lowers the impedance of the incoming signal. These devices require either battery, 48V phantom, or AC power. Passive direct boxes alter the impedance by way of an internal transformer and require no power.

While many DI boxes simply convert your signal, others offer additional features. For instance, the Behringer GI100 adds speaker simulation. Radial Engineering's JDV active direct box (as well as several of the company's other devices) has a circuit called Drag Control, which is designed to re-create the relationship between a guitar pickup and a tube amp in situations where you're using a solid-state input device. It gives you a knob that alters the impedance load to your pickups, letting you dial in the most natural sound. Radial also offers a standalone Drag Control product called the Dragster.

Quality Is Key

Not all DI boxes, preamps, and other input devices sound the same. Just as different mic pres yield different sounds when fed by the same mic on the same source, different input devices give you different sounds from the same guitar. The quality of the input device's components is a key factor.

Use the highest-quality input device you have access to, and find one that works well with your guitar. Even if you're going to be reamping the part later, it's still important to start by recording the best possible sound. A number of engineers I've spoken with like to use a tube preamp for DI guitar parts, because they feel it helps inject a more realistic tone, even to a part that will later be reamped. (In the process of reamping, you take a clean DI guitar track and patch it out to an amp, first going through a dedicated reamping processor to convert the output to an impedance appropriate for a guitar input, and then rerecord it with a mic through the amp. See the sidebar “Reamping the Old-Fashioned Way.”)

Decisions, Decisions

When deciding how to record a DI guitar part that will be processed with a modeler, you have one fundamental choice: will you record the modeled tone directly onto a track of your sequencer or multitrack, or will you record it unprocessed and insert the processor's tone during mixdown? There are advantages to each method, and your gear may dictate your decision.

Most outboard modeling processors are better suited for use as direct boxes that output a processed sound to a recording device, rather than as insert effects that are used on unprocessed, previously recorded guitar tracks.

Generally, modeling processors have only high-impedance inputs, which aren't designed for the line-level, low-impedance outputs that you would need to connect them to if you were using them as inserts. So unless your processor has line-level inputs (such as the Line 6 Pod XT Pro and the Tech 21 SansAmp PSA 1.1), its architecture dictates that you use it as a DI and record its processed sound to disk.

Many outboard modeling units (for example, the Line 6 Pod XT, the DigiTech GNX4, and the M-Audio Black Box; see Fig. 2) have USB outputs that allow them to function as audio interfaces in their own right. Alternatively, you can plug their analog outputs into the line inputs of an audio interface.

Perhaps the biggest advantage of recording through an outboard modeling processor is simplicity. Just as if you were going through an amp (or an amp with effects pedals), what you hear is what you get. Find a tone you like, record the track with it, and you're done. Because your signal is being processed before it hits the computer, latency is not as big an issue as it is when using a plug-in modeler.

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SIDEBAR
REAMPING THE OLD-FASHIONED WAY
Although you can reamp with a modeling plug-in in your sequencer, or a modeling effect in your personal digital studio, the traditional process of reamping entails taking a guitar track that's already been recorded and patching its output to a guitar amp (see Fig. A). You then play back the guitar track with a mic (or mics) on the amp and rerecord it onto a fresh track.

It's not advisable to simply take a line out of your sound card or multitrack and run it into a guitar amp for reamping. The line-level signal will be mismatched with the high-impedance input on your guitar amp. You'll need to run it through a box such as the Radial X-Amp, or the Little Labs Red Eye, which converts your line-level signal back to a high-impedance guitar signal suitable for plugging into an amp. You could also plug the converted signal into an outboard modeling processor.