Recording the live amp after the fact…
By Darwin Grosse
The recording options for electric guitar players change constantly. Not long ago, the primary means of recording the instrument was to plug into an amplifier and mike the cabinet; everything else was seen as a poor substitute for “The Real Thing.”
The last few years have seen new hardware and software come onto the scene that allow direct recording of an instrument with an attempt to replicate the sound of a miked amp. For people who aren’t sufficiently convinced by this technology, another branch of recording gear is available that will allow you to run your recorded signal through an amp, restoring that dynamic into the recording chain.
In this article, we will review the options available for electric guitar and bass recording, with some ideas for increasing the flexibility of your recording system.
DI (Direct Injection) recording bypasses the traditional amp and takes the pure signal from your instrument directly to tape or DAW. Well, more or less directly. Generally a device like a DI box (see below) is used for one or both of the two things that need to happen to get your instrument’s signal into shape for recording:
• Amplification, so that the signal is hot enough to drive the recorder.
• Impedance adjustment, so the signal is properly transferred to the recording device.
Amplification is rather obvious—the output of most instruments is far too low to drive a recorder’s input. Almost any type of preamp will do for this process; in fact, many DI devices don’t provide amplification, assuming that you will use the preamp found in a mixing board.
Impedance adjustment is another beast altogether, and one of the least understood interface issues in the recording world. In short, all audio devices have both an input and output impedance, which determines the internal “resistance” of the device. For the best interface between two devices, you want the output device to have low impedance, and the input device (for example, the mixer channel) to have a much higher impedance. Impedan ce adjustment is required to allow the instrument’s signal to “flow” more easily from the instrument to the recorder.
Because of the nature of magnetic pickups, most electric string instruments are high-impedance devices, so the mixer channel would need to have an ultra-high impedance to allow a decent flow of current from the instrument. Few mixer inputs have this level of input impedance. If an adjustment is not made, you will probably notice a lack of high end in your signal, and also a very dead sound as the output signal is “damped” at the input. Obviously, this isn’t desirable, so the use of some specialized hardware for DI recording is in order.
Beyond the DI box
For years, DI recording has used a simple box (generically called the DI box) to adjust the impedance of an instrument and alter it to interface with a mixer channel. These boxes can be fairly inexpensive, since passive DI boxes are often just a transformer and a few connectors.
The use of DI boxes is common for bass recording, but they don’t have any particular “sound” and were therefore maligned by guitarists. The first breakthrough for guitarists (and tone-hungry bassists, as well) came in 1989, when Tech 21 came out with the SansAmp direct module, which combined the function of a DI box with some custom analog circuitry that provided amp-like tone without the need to actually record an amplifier. This was hailed as a great achievement by both studio and bedroom engineers alike, and became widely copied.
Line 6 pushed the envelope even further in the late 1990s with its POD effects units. These devices not only include cabinet simulation, but a host of effects pedal simulations as well. With the POD (and its many emulators), you can now create a complete, produced guitar sound without the muss and fuss of pedals, amps, speakers or microphones. At this point it’s difficult to find an effects unit or preamp that doesn’t have a “cabinet simulator” built into it, and direct-connect recording tools are now in common use by many players. It’s hard to find a desktop hard disk recorder now that doesn’t have at least one dedicated Hi-Z (high-impedance) guitar input and some guitar-friendly effects on board.
Now in software
The software guys wouldn’t be left out of this market, and the result is the latest addition to direct recording tools: software amp simulators. Probably the best known of these is IK Multimedia’s AmpliTube, an amp simulator that features a variety of preamp, power amp and speaker simulations; it has become a staple in many recording studios. This software features amazing flexibility and playability, and has set a high bar for other simulators that appear as host-based and DSP processes. Heaven, ain’t it?
Well, not everyone thinks so. While guitar and bass amps have become ever more virtualized, a subspecies of recording enthusiast pines for the lost amplifier in the recording chain. There are a number of effects that occur when an instrument’s signal is subjected to tubes, amps, speakers, air and microphones, and these die-hard adherents believe that no amount of modeling can properly replace the amplifier.
To a certain extent, they are absolutely right. While a modeled amplifier may, in fact, be able to give the tonal quality of an idealized preamp/amp/speaker combo, how can it model your recording space, microphone selection and particular amplifier? It can’t—and this is where reamplification comes in.
The technique of reamplification is commonly referred to as “reamping,” although this takes liberties with the trademark of REAMP, Inc.
Reamplification in a way reverses the DI process described above. It takes a guitar or bass signal that was recorded via DI, and sends it back out from the recorder to a real amplifier where it gets miked, the miked signal being recorded onto a separate track.
By doing this you can effect the signal and use your mic setup to capture some “real air” speaker tone with the recorded guitar or bass. In addition to allowing for flexibility in processing, this also allows you to lend a reality to the sound, and can really help the track sit in a mix. Anyone with a home studio where the noise from cranked amps isn’t welcomed by cohabitators or neighbors can nevertheless go ahead and record the guitarist via DI, and later arrange for a reamplification session where or when the noise is no hindrance.
The previously recorded signal from your multitracker is not quite the same as that which came off the guitar or bass, of course, with the result that many amps don’t sound quite the same when asked to amplify a previously recorded DI guitar track as opposed to the original signal from the guitar pickups. Careful adjustments of the amp’s input controls and of the source level are often enough to give good results—folks have done this for as long as guitars, DI boxes, amps, and recorders have been around. But there is a better way.
Recently, reamplification has come into its own with the development of application-specific devices. The most well known of these is, well, the box made by REAMP, Inc. Recording engineer John Cuniberti came up with the concept while he worked with his clients, and founded the company to produce his patented device. As reamplification has become more popular, other companies have taken alternative routes to the same ends, and there are now several reamplification boxes on the market.
The basic job of a reamping box is to reverse all of the DI processes described earlier, including gain and impedance adjustments. This results in a signal that is acceptable for an amp input. Each of the implementations from the different manufacturers takes a different approach to altering the signal; for example, the REAMP box uses a custom transformer to provide a more guitar pickup-like reaction to signal changes—in fact, in the licensed version of the REAMP system found in the Millennia TD-1, there are two different transformer windings to simulate different guitar systems.
The result of using a reamping box, as compared to simply plugging the output of a multitracker or mixer channel into an amp, is evident on first listen; the dynamics of the original signal are reproduced much more clearly, and your amp will “speak” rather than simply howl.
Often, virtual amps cannot match the results of reamplification. The obvious difference, especially among tube aficionados, is the interaction of preamp and recorded signal. In the tube domain, each amplifier has its own characteristic, and the amp that you have will be unlike any other. A tube amp’s reaction to player dynamics, sustained playing and subtle picking techniques is very individual, not likely to be reproduced by an “idealized” model.
Beyond that, reamplification gives you the flexibility of miking a cabinet, but without irritating a player (or yourself) as you make the subtle adjustments necessary for recording the best sound. This should not be underestimated—having the ability to quickly grab a recording, but being able to alter the microphone placement or even swap out amps after the fact, provides flexibility equal to that of a software plug-in on your DAW.
Of course, tweaking or exchanging amplifiers and adjusting mic settings are not the only advantages in reamplification. It also provides you with editing options that are much more flexible than live recording could ever be. For example, many guitarists like the playability provided by reverbs and delay lines—in fact, their performance would suffer without them. If you record this delay-filled performance, but later decide to comp a number of guitar parts into a single “master” performance, you might be out of luck—the effects recorded in each performance will not match one another.
Instead, you can DI record the guitarist’s performance (dry) while letting him use his effects and amp for monitoring—he’ll be much more inspired hearing himself playing a full-throttle part with amp and effects than he would be trying to wring emotion from the plinky-plink of a plain vanilla DIed guitar. Later, you perform your edits, then reamp the edited track. Now you can add effects that fit the comped track, leading to a more convincing guitar sound.
Reamplification also opens the door for experimentation that no virtual amp module is likely to attempt. For example, you can get very interesting results if you record a rhythm guitar track where the amp faces a corner, and the mic is placed in the cramped air space. The result is a stack of resonances and cancellations that is difficult to emulate with software, but gives an interesting “phase-y” quality that can be perfect for a backing track. There is also the old trick of recording a Pignose or similar practice amp from the inside—another example of a sound that is unlikely to be emulated by any software company.
DI and reamping—a cool combo
As you can see, the combination of DI recording and reamplification opens a number of options for the project studio; from experimental mic and amp placement to flexible amp and effect replacement, a wide range of recording problems can be solved with these techniques. The more particular you are about your guitar tone, the sooner you will be seduced by reamping options.
While the use of DI and reamplification doesn’t provide the “silent studio” and automation options of cabinet simulation, it lets you use familiar tools without limiting your editing options. Reamplification has shifted from an ultra-tweak technique to common use, and is an important part of today’s engineering bag of tricks.