Guitar Amp Recording Part 3

Written by Mike Senior, SOS

Single-Mic Techniques

Even working on the assumption that you're only using one mic, the professionals have an awful lot to say about where you might put it. For a start, it seems to be fairly common practice to audition the different speaker cones of your guitar amp. "They're supposed to sound the same," says Roy Thomas Baker, "but if you're using a 4x12 cabinet, each of these four speakers may sound different." While there's nothing necessarily wrong with plonking your mic right at the centre of the speaker cone if it gets what you're after, a lot of producers take the time to experiment with different positionings off axis, where the sound is typically warmer. Mike Hedges: "Depending on where you have [the mic] — outer speaker or inner speaker — you get the difference in tone from the edge of the speaker and the centre of the cone."

In fact, Mike Clink also tries small changes in position even when working with basically on-axis sounds. "I'll point [the SM57] exactly dead on, though I might move it an inch or two to get the right sound." Directional mics, such as cardioids and figure-of-eights, exhibit different frequency responses off axis — broadly speaking, off-axis sounds tend to be duller, although it's a complex effect which is different for each model. Professional producers are well aware of this, and employ the effect to refine their sounds. For instance, Chuck Ainlay comments "I'll usually start with a [Shure SM57] on the amp; but not straight on axis with the middle of the speaker; it's usually off-centre, angled towards the middle of the speaker and generally just off the grille." Jay Graydon refers to a fairly similar setup: "I position the mic about one inch left of the edge of the speaker-cone centre, using a 22-degree angle, and about one inch back from the grille cloth." Andy Johns, on the other hand, has said that "the miking technique I used on electric guitars for years was two [Shure SM57s], one straight on, and one at 45 degrees. Put 'em together, and it always works." The question of how far away to place your mic really divides opinions.

While Chuck Ainlay's 'just off the grille' seems to express the majority view, Bill Price preferred a position six inches away on the Sex Pistols sessions, while Steve Albini usually starts from around 10-12 inches away. Alan Parsons, on the other hand, avoids close placements: "Every engineer I've ever come across has always had the mic touching the cloth, and the first thing I do is move it away literally a foot. Let's hear what the amplifier sounds like, not what the cabinet sounds like... I might have it even further away if it's a really loud 4x12 cabinet — as much as four feet away." Ben Hillier also extols the benefits of more distant placements, up to six to eight feet, when he's trying to capture his favourite 'amp in a room' sound.  All speaker cones are not created equal! Normally, if an amp or speaker cab has more than one speaker cone each will sound different, and it is worth finding out which one you prefer. You can even try recording two different cones and blending the sounds, as described above  

 Audio Examples: Miking Different Speaker Cones SM57Left SM57Right SM57LeftSM57Right

To compare the sound of the Fender Twin Reverb's two speakers, I placed Shure SM57s directly over the centres of the different cones, on axis and right up against the grille. This also gave me the opportunity to try out the dual-mic technique mentioned by Steve Churchyard. You can hear the range of sounds available from mixing the mics in the third audio example, which starts with the left-hand SM57, but then fades in the right-hand SM57 until, by the middle of the example, both mics are at equal level. The left-hand SM57 then fades out during the remainder of the audio example. C3000Left C3000Right C3000LeftC3000Right

Here's a stab at Tony Platt's dual-mic AC/DC technique, using two large-diaphragm condensers, about six inches apart and pointing at different speakers, placed about six inches from the grille. In the third example I have panned the mics a little left and right respectively, to demonstrate the stereo spread effect he talks about.  

Two Mics Together

One of the things that initially surprised me was that coincident dual-mic techniques, where the two mics are placed as close as possible to each other to minimise phase cancellation between them, actually appear to be more commonly used than single-mic techniques. John Leckie explains: "There's an amazing difference in the sound and colouration you get from adjusting the balance of each of the mics, and you can get radically different textures depending on your mix of the two." The majority of favoured mic pairs seem to include the trusty SM57, but its most popular partner appears to be the larger-diaphragm MD421 — users include Bob Rock, Bruce Fairbairn, Alan Winstanley, Joe Barresi, Simon Dawson, Stephen Street and The Matrix.

Also high on the list is the pairing of the SM57 with a large-diaphragm condenser of some type, and Steve Churchyard, Toni Visconti, Jim Scott, Stephen Street, and John Leckie all name-check the U87 in this role. However, John Leckie states an interesting preference for an SM58 and U67 rig instead: "SM57s tend to be that little bit brighter than the SM58, which really isn't what you want when you're miking up an electric guitar amp. You really want to pick up a flat signal, an 'unstimulated' signal I suppose is the word... The U67 gives you the warmth and a broader sound." Referring to this setup, Leckie also explains more about what makes double-miking so powerful: "If you brighten up the U67, it's totally different to brightening up the SM58, so sometimes I'll add a little brightness to the 67 and a little compression. But between that combination, I find I can get pretty much everything I need. They're rarely used at equal level; sometimes I'll favour the SM58 with the U67 at 10-15dB down. Even 20-30dB down, just bringing it in, it's amazing the different colour you get — how much the tone of the guitar changes." Coupling an SM57 with a small-diaphragm KM84 condenser finds favour with Bill Price and John Fry, while Mike Hedges chooses his favourite Sennheiser MKH40.

Bill Price also mentions the importance of finding a very close phase match between the two microphones. "What one had to do was balance those mics equally, grab a pair of headphones out in the studio that were turned up nice and loud, and fractionally position one of the mics so that they were perfectly in phase at high frequencies, because if you had one mic five inches away and the other six inches away you'd obviously get really bad phase shift that would take the top off the guitar sound." Beyond specific favoured mics, a number of engineers also mention more general principles when choosing pairs of mics for guitar recording. Jim Scott and Stephen Street both mention using a 'cheap' or 'bad' mic with a good mic (both give the SM57+U87 combination as an example). "Between the two you can find the ideal sound," remarks Jim, "and you can get brightness and fullness." Steve Albini, on the other hand, finds it useful to think in terms of blending 'bright' and 'dark' mics. "Normally I'll have two microphones on each cabinet, a dark mic and a bright mic, say a ribbon microphone and a condenser, or two different condensers with different characters." Eddie Kramer's discussion of his Hendrix sessions reveals a similar preference: "Generally speaking, it was either a U67 or a Beyerdynamic M160, or a combination of both, which I still use today. It might be slightly different, of course, but the basic principle's the same — a ribbon and a condenser."  The 'Vortex' setup described by Chris Tsangarides, is a great way to add ambience. The setup pictured above is a variation created by the author for a small studio, where one of the walls was used in place of baffles for one side of the flare.  

Audio Examples: Ambient Mics & The Vortex SM57Close C3000StereoAmbience SM57C3000Ambience

To illustrate the possibilities available from ambient mics, I recorded the same guitar performance with three mics simultaneously: a Shure SM57 close mic on axis to the centre of the speaker cone and up against the grille, and a stereo pair of AKG C3000 large-diaphragm condenser mics a few metres away. The third audio example illustrates the range of sounds available by mixing the close and ambient mics. The example starts with the SM57, but then the ambience mics fade in until, by the middle of the example, all mics are at equal level. The close mic then fades out during the remainder of the audio example, leaving just the ambience. VortexMic1 VortexMic2 VortexMic3 VortexMix

These examples give some idea of how Chris Tsangarides' Vortex technique can sound, even when adapted to suit a smaller room, as I've described in the main article. The guitar cabinet was set up in the corner of the room, with a single, large acoustic panel making up one side of the 'flare'. All the mics were large-diaphragm condensers: the first, an AKG C414B XLS, was on axis over the centre of the speaker cone, right up against the grille; the second, an AKG C3000, was two metres away, pointing at the cabinet; and the third, another AKG C3000, was four metres away, angled to catch the reflected sound from the control-room glass. The final audio example starts with the C414B XLS close mic on its own, then fades in the two ambience mics (panned a little left and right) until, by the middle of the example, all the mics are at equal level. The close mic then fades out during the remainder of the audio example.  

Many thanks to www.soundonsound.com for this article