Recording Guitars: Miking Amps, Part 2
If you want to get professional sounds from home-studio recordings, you need to learn some basics of recording technique. However advanced your digital recording system might be, the results will never sound like studio-quality recordings if you don’t get quality sounds into the system in the first place.
As far as capturing great electric guitar tones, a large part of your studio technique will revolve around microphone placement. Part 1 of this new series from Gibson looked at positioning single mics on guitar amps; this installment will examine some multi-mic placements, and a few little tricks to help make them work for you.
Very often a single microphone will capture all the amp tone you need. Using a single mic also has the benefit of minimizing phase cancellation issues, although it won’t necessarily eliminate them. Phase cancellation can hamper an amp tone when signals from two different mics cancel some frequencies or create unpleasant dissonances, which are caused by the “out of phase” relationship of sound from two different positions. See Phased and Confused below for some tips on dealing with these issues. With that caveat, the perfect guitar sound for your track will sometimes be best captured by using two microphones in different positions around the room. Here are some methods to try out.
This is far and away the most common form taken by multi-mic placements, and is intended to simultaneously capture the punchy, in-your-face sound of a direct mic positioned an inch or less from the speaker and the airy, spacious, slightly reverberant sound of the amp in a room. The room mic is the “ambient” mic, and is usually a condenser, while the close mic is usually a dynamic mic, but you can try whatever works for you. As a starting point, try placing the dynamic mic slightly off-center on the speaker, about half an inch away, and the ambient mic six feet back, and six feet high. Move them around—you’ll find the distant mic will have a lot of options, and you might move it further, or closer, up or down—and tweak the mix accordingly. You can either mix down the two mic signals to one signal that you send into your DAW (or multi-track tape, if you’re going analog), or record each on an individual track to process and mix later, if you have enough available channels in the system. For the best possible blend of a close/ambient mic pair, try getting the best individual sound from each first, as explained in Part 1, then putting the two together.
To capture two speakers in a multi-speaker cab, or to record a bigger sound that delivers the response of two different microphones in similar positions on one speaker, you can try using two mics in a close or semi-close placement. If you’re using two different mics on a single speaker, place the receiving ends of each (known as the “capsule”) as close together as possible, without touching, in order to minimize phase cancellation. This technique might seem redundant, but can often yield outstanding results, allowing you to blend the characteristics of two different microphones to capture one amp sound, a bright, detailed condenser and a punchy, midrange-heavy dynamic, for example. On guitar cabs carrying two or more different speakers, try miking each speaker separately, placing each of two mics—of the same type, or different—at the same distance away. Some amp makers use two different types of speakers in 2x12 cabs to fatten up the tone, and this miking technique will make the most of those. Even two different speakers of exactly the same type, however, will often sound slightly different, and blending them might yield great results.
Front-and-back: Interesting sounds can often be captured by miking the back of an open-backed speaker cab, too. You can use your single-mic techniques on the back of the cab by placing the mic close to or even into the opening in the back of a combo or extension cab (I find the back-of-cab sound is usually a little more raw, fat, and warm than the front-of-cab sound). Or use two mics to close-mic the front of the cab and the back of the cab. Be aware that you will need to reverse the phase of one channel when using this technique, since the sound produced by the back of any speaker is always 180 degrees out of phase with the sound produced by the front of the speaker.
Also, be aware that however hard you try, your two-mic sound just might not sound as good as one mic on its own. This might be curable with some attention to phase cancellation issues, but it might just be the way the sound is working for you that day. In that case, there’s no shame in going with the one-mic sound. Do whatever sounds best in the track.
Phased and confused:
When using two mics on a single amp you will almost always encounter some phase cancellation issues; whether they are bad enough to cause a problem, or even to be heard, depends on the situation. First, ensure it isn’t an entirely reverse-phase mix by flipping the phase of one of the two channels and listening again (many DAWs include plug-in “reverse phase” functions that you can use right on your virtual mixer, too). If your two-mic sound goes from hollow and bottomless sounding to fat and full, you had a reverse-phase issue. Once you know that both mics are at least in phase with each other, you can try moving the position of one around until the phasing issues are less obtrusive, which is simply determined by finding a pair of positions that are really smoking tone-wise. Alternatively, you can often fix phase issues in the digital realm. Record your two-mic signal on two separate tracks, then zoom in on the sound waves (soundbites) in each of the two channels in your DAWs editing window, and drag or nudge the soundbite of the ambient mic forward a few milliseconds at a time until the soundwaves line up perfectly. Listen again, and you should hear a very different blend.
You can even experience phase cancellation issues with one mic, which are usually caused when a lot of reflected sound—sound waves bounced off a hard surface in the room—is picked up by the mic simultaneous with the direct sound. Sometimes reflected sound contributes to a great recorded sound, providing air, depth, and ambience. Other times, however, the time delay of its reflection creates detrimental phase issues. To minimize detrimental reflected sound, observe any hard, reflective surfaces in your recording space such as wooden floors or hard walls, large uncovered glass windows, and so forth, and dampen them down with some acoustic foam or even, temporarily, a heavy blanket. Listen again, and tweak accordingly.
There are no hard and fast rules here, other than the sin of not experimenting at all. Play around with your mic placement, have fun with it, and you’ll discover some powerful new recording techniques.
Check out Recording Guitars: Miking Amps, Part 1 here.
[originally Dave Hunter | 01.07.2008, Gibson.com]