Below we present a range of recording techniques, starting with the simplest -a single mic- and moving on to several microphones of different types, multiple amps, line signal, reamping... to record those guitars while opening up alternatives for the mix.In the September issue we covered the first part of a special on electric guitar amplifiers: Matchless, Mesa Boogie, Vox... To record a good guitar sound, the first step is without a doubt to have a good amp and a good guitarist. From there, there are literally hundreds of ways to record this instrument. Logically, the technique to use is dictated by the final sound you want to get and, in turn, that sound depends on the style of music and, ideally, on the role the performance will play in the song (lead guitar, doubled part, background arrangement, etc.). Generally, the musician recording will be the one who sets the style. However, you don't always know how the guitar being recorded will be used, whether because the mix will be done at another studio, because alternatives are being tried out and nobody knows where that guitar will end up, and so on.
One mic
Many will agree: if you know exactly what's going to be played and the guitarist is good, the best thing is to put a Shure SM57 (or a similar dynamic mic) in front of the cone and let the guitarist play. It's that simple. Where should you place the mic? A good starting point is usually a few centimeters from the cone, perpendicular to it, and pointing somewhere between the center and the point where the cone itself begins.
Generally, the closer the mic is to the center (Fig. 1: white cross), the more compact/powerful/bright the sound, and as it moves off-axis toward the outer edge of the cone (marked with a black cross in Fig. 1), the sound gradually loses some of that definition. This makes sense, since physically the edges of the cone don't follow the movements of the voice coil as faithfully as the parts of the cone closest to it do. With this in mind, for certain applications, aiming farther out on the cone can give a warmer sound, or a more broken-up sound in other cases. So it's worth trying different positions to see which one gives the sound you're after, bearing in mind that when close-miking amps, small movements of the mic can make big changes in the resulting sound. Along these lines, don't forget to also try changing the angle of the microphone, tilting it toward the inside or outside of the cone so that it isn't perpendicular to it.
As for distance, the closer the mic is to the speaker (or to the protective grille/cloth), the more immediate ("in your face") the sound will be, although you have to make sure the proximity effect doesn't send the lows through the roof, and pay attention to the amp's own noises being picked up (hiss, hum, clicks...). It's not unusual to remove the protective grille/cloth to get the mic closer to the speaker, to see better where to place it (a flashlight can help if the grille can't be removed), or because the grille itself vibrates or gives the amp a metallic sound. As mentioned at the start, the choice of mic distance should take into account the role the guitar will play. If it's an arrangement that will sit in the background of the mix, it makes more sense to move the mic back so that it captures more ambient sound and doesn't sound so up front, and vice versa; it's hard to bring forward a guitar recorded with a lot of ambience.
As for the type of microphone, dynamics are used very often, since they handle high SPLs and their internal workings get along well with the sound of an amp. Along with the omnipresent 57, other dynamics commonly used for this task are Sennheiser's e609 and e906 and, moving up the price scale, the MD 421 (Sennheiser), Electro-Voice's RE20 or the MD 441 (Sennheiser). Generally, dynamic mics deliver a sound with plenty of punch. If you're after a less aggressive sound, a ribbon mic may be more suitable. Even on heavily distorted guitars, a ribbon mic usually provides a certain warmth compared with dynamics. The manufacturer Royer has led this field in recent years, especially with its R-121 model. It has just launched a new, more affordable model -the R-101-, which joins a market where other offerings also stand out, such as Groove Tubes' Velo-8 or Beyerdynamic's M160. If your budget is tight, you can try ART Pro Audio's M-Five, Cascade Microphones' C77 or Apex's 215.
However, depending on the tone you're looking for, a condenser mic may be more suitable. Generally, large-diaphragm mics are used, placed a bit farther from the cone than dynamics. This gives a more open sound, very well suited to clean tones, for example. Historically, many mics have been used for this, from AKG's 414 to the C12, by way of the Neumann U67 or U87... Today, practically every manufacturer has models of this type: Audio-Technica, Blue, Avant, Cascade, SE, Shure, Violet Design, etc.
Two are better than one
With all of the above in mind, to have more options it's common to place a pair of mics in front of the cone so that by varying the proportion of each in the mix you can change the timbre (a kind of microphone EQ). A pairing that works very well for hard-driving guitars is a dynamic and a ribbon, each covering a different part of the cone (but at the same distance). If the dynamic dominates over the ribbon, the sound tends to be harder, and vice versa.
For clean sounds, placing a dynamic close to the cone and a condenser farther back (at distances of up to about 1 m) also usually works very well. The dynamic provides definition, and the condenser adds body and depth, since it picks up more of the room.
As always when using more than one mic on the same source, you have to be careful with the phase between them. Again, on electric guitars, small movements can make big changes. If the mics are placed at different distances from the cone, the three-to-one rule should be followed, and if they're placed at the same distance, the adjustment should be made based on where the mic's diaphragm is, not the end of its grille. A quick way to check this alignment is to record a snippet and zoom in to sample level in the DAW.
In this situation, it's possible that when you sum the two mics there will be cancellations. A quick listen will tell you (usually lows or highs disappear). If there are problems, you'll have to move one of the mics slightly (a few centimeters or millimeters) until the two work together. As a second option, useful if the mics can no longer be moved, the adjustment can be made in the DAW by applying a small delay to the earlier signal. Generally, this has to be done with a plug-in that works in samples, because if you do it in milliseconds, one millisecond of delay is equivalent to a distance of about 34 cm... perhaps too much. (The speed of sound at 20°C is 343 m/s, or in other words, 34.3 cm in one millisecond.) Several plug-ins let you do this, from those built into each DAW -which usually only let you delay the signal- to more complex ones like Voxengo's PHA-979, with M/S and pan controls, or Sound Radix's Auto-Align, which makes the adjustment automatically.
An additional benefit of having two mics is that you can spread them in stereo. When both mics are placed close to the cone, the resulting image isn't extremely wide, but it does give a less localized and somewhat broader sound.
More mics
As mentioned earlier, mics placed farther away pick up more of the room and, if the room sounds good, this can make the guitar sound fuller and deeper. That's why additional room mics are often placed farther from the amp (several meters), which can later be combined with the close miking. This can be done with a single mic (in mono) or with a stereo pair (XY, A/B, ORTF, etc.). Condenser mics will capture more detail, which can be very useful, although they can also sound too bright in some cases. In that situation, ribbon mics will generally sound warmer.
If you can't mic the room, an alternative is to emulate it with reverb, using a Room or Ambience program. If you're not sure where to start, most plug-ins have presets like "Guitar Room" or "Guitar Amp Room," which can be a good starting point.
On another note, there are cases where it can also be worthwhile to mic the back of the amp, which usually radiates more low frequencies. Tube mics tend to give good results; just keep in mind that you'll probably have to invert the polarity relative to the front mics.
Multiple amps
To continue with the options, the next step might be to use several amps at the same time. To do this, you use a splitter or take advantage of an amp's parallel output to drive the amps simultaneously. Miked separately, a single take gives you several different amps to choose from later in the mix, whether to go with one of them or to use them in combination. Very often, the sound of those massive guitars typical of some American productions is the result of many different amps playing at once.
If you pan one amp's sound to one side and another's to the other, you generally get a fairly wide stereo image, although keep in mind that it won't sound like two independent guitars. To get that effect, you'd have to record a new take or use the old trick of delaying one of the two sides by a few milliseconds (somewhere between 3 and 20 ms, and find what sounds best, both in stereo and in mono). Of course, the latter could be done having recorded only one amp, but it's generally more effective when two different ones have been used, because the left and right signals differ more than when it's the same signal.
Another benefit of using two amplifiers is that the room sound is usually richer and more powerful, since the signals from the different amps add up acoustically in the space. Some engineers, even when recording distorted guitars, also record an amp with a clean sound that they later add to the distorted sound to get a bit more body and definition.
Line signal: Reamping
And to round out the recording options, another alternative is to also record the "line" signal coming from the guitar on a separate track. To do this, you simply use a good DI box: the box's parallel output goes to the amp/pedals and the balanced output goes to a preamp and then on to the recording system.
On the one hand, the waveform of this signal is often very useful for editing, since the guitar strums and notes are usually much easier to see than when the signal has gone through pedals and an amplifier. Often this signal is recorded only to be used as a visual reference, although it can serve many other purposes. For example, you can always feed this track into an amp emulation plug-in like Amplitube. The result can be combined with the signal from the real amps, or even replace it if in the end the amps' sound doesn't work. The sound of these plug-ins has improved incredibly over the years.
Another useful way to use the line signal is in home studio settings. If you don't have a suitable room or can't make too much noise, you can record on headphones using an emulation program and then send that signal to a professional studio to have it reamped. This term means "re-amplifying" (or re-amp). The idea is simple: once you have a signal recorded, you hit play, and the output of the recording system is used to drive one or more amplifiers, which in turn are recorded with one or more mics.
For many years, this technique has been used to improve sounds that weren't quite working (not just guitars; also kick drums, snares, etc.), as an effect on vocals and other instruments, to get real ambience... In the case of electric guitars, the process can be done even if you only have an amp signal that doesn't quite measure up, but it works especially well if you have the "clean line" signal.
The process of feeding the recorder's signal back into the amplifier can be done in several ways, but the simplest is to use a device designed for it: reampers, which take care of adjusting the signal level and impedance and usually offer other useful options, such as a control to set the signal level, a polarity inverter or ground loop eliminators. (Let's not forget that an amplifier input expects the signal level and impedance of an instrument, and the signal sent by a recorder is completely different.) One of the best-known devices is the Reamp, which costs around $190 (plus shipping), although there are somewhat more affordable ones, such as Palmer's Daccapo (about €80) or Radial Engineering's Pro RMP (around €100). The latter manufacturer also has active models that let you send the signal to several amplifiers at once (the X-Amp model).
