Amp Miking

Adding a miked amp to your direct signal changes your tone, since a microphone, amplifier, speaker, and the cabinet are now in the equation. They're all essentially signal processors, and the way you use them makes a big difference in the final, mixed, sound.

The Grille Cover

A grille cover is a passive filter that can affect frequency response, and if it rings or resonates, it may buzz like a blown speaker.
Once a cabinet is in place in the studio, if it's easy to remove the grill cover, do so. The sound simply gets better. However, don't let a mike hit an exposed speaker; be sure to anchor the mike carefully.

Mike Positioning

It helps to have someone else, like a second engineer, to adjust the mike position while you're in the control room. Any type of mike can work : dynamic, condeser, or ribbon. If the amp will be fairly loud, use a dynamic mike; these deal best with loud sound sources. (The sound engineers rule of thumb; "Never put a condenser or ribbon mike where you wouldn't put your own ear).
Whatever mike you select, choose one with an even bottom-end frequency response.

For a single-speaker cabinet, start by positioning the mike in front of the speaker, directly facing the cone. To capture the punch of the moving air, mike very closely, about one inch back from the grille cover ( or where the grille cover was, before you removed it ). Pointing the mike at the speaker cone doesn't allow for much low end, though, so more upper-mid frequencies will come through.
As you play, have someone slowly move the mike toward the speaker's left or right outer edge. You can also try moving the mike toward the top of the speaker, but only if the amps electronics are not right over the speaker. If you're using a combo amp, and you're picking up hum or noise from the amp's transformer, move the mike to the other side.
If that doesn't solve the problem, move the mike toward the lower part of the speaker. The sound bouncing off the floor may cause phase anomalies, so consider putting the cabinet on a chair, or something similar.

Also, when an amp sits on the floor, there is a buildup of low end; this may not be a problem when recording, unless you notice uneven lows. If so, raise the amp or reposition the mike.

Sometimes you'll find a mike position where the bottom end sounds good, but there aren't enough mids. In this case, try tilting the mike slightly toward the cone at about a 22 degree angle.
If the cabinet has more than one speaker, mike each to find the best sounding one. Use that speaker mostly for the bottom end, pointing the mike at least halfway between the cone and the edge. Then, for the mids, point a seperate mike directly at the center of the second-best-sounding speaker. Experiment with both mike positions.
Important : With two or more mikes, keep them the same distance from the cabinet so both will recieve the sound at the same time. If there's a difference you may get phase problems, which can cause frequency buildups and cancellation. If the board has a phase shift on every channel, blend the channels in mono, flip one channels phase switch, and use the position where both mikes combined sound is stronger.
And if you're combining the mikes with a direct signal, check its phase against that of the combined mikes, too.

Here's a YouTube video for some demonstration:
Basic Recording Techniques: Electric Bass

Anchoring The Mike Stand & Cable

Merely positioning the mikes is not enough, it has to be stable.
Most mike-stands bases can tip easily. The heavier the base, the better. Anchor the stand with sand bags or any stable, heavy object that will not slip or or rattle. Placing three 20-pound sand bags around the base is ideal. While positioning the mike, wrap its cable around the stands boom a few times, and leave a little slack so the cord doesn't pull and change the mike's position. To keep the cord from moving, tie it to the stand, using removable cable ties. Don't use permanent cable ties, as you will have to cut the tie later, and risk damaging the cable. Velcro cable wraps are the easiest to set up and remove. Duct tape also works, although it leaves a residue, and aren't always that easy to remove either. There should be very little cable slack at the mike-stand base.
Secure the cable to the floor. On wooden floors use duct tape, and cross the cable with tape in one-foot strips at least every two ro three feet. Avoid duct tape on carpeted floors. Instead, put throw rugs or carpet remnants over the cable.

Speaker Types

Speakers can really affect an amp's sound. Cheap speakers (with small magnets and flimsy construction) don't sound as good as speakers with bigger magnets and better components. Although, in this day 'n' age, it isn't THAT simple to tell if a certain speaker sounds good or not, just by taking a look at it!

Different-size speakers sound different, even if they're high quality, have similar specs, and are adequately rated to handle the same wattages.

- 10" speakers, sound punchy, because of their relatively small size. Since there's less speaker-cone mass to move, the air moves back-and forth quickly, resulting in a quick responce. They give a natural midrange and defined pitch center, but produce less bottom than larger speakers.

- 12" speakers, have intermediate punch and bottom. Quality 12" speakers are a safe choise.

- 15" speakers, provide less punch, but deeper lows.

- 18" speakers, are generally too bottomy-sounding for recording, not because of excessive lows, but because of poor midrange to balance. Boosting the amps mid frequencies may helps note definition, or you can use an 18" speaker along with a 10 or 12" speaker.

In terms of cabinets, open-back types typically have less bottom than closed-back models, but may offer a more even-sounding responce, since the cabinet can "breath". Closed-back cabinets are more common for bass amps as they generally provide more low end.

Ground Zero

Before plugging ANY mikes into the mixing console, set the board's faders all the way down.
In fact, whenever you start a recording session, it's a good practice, to "zero out" the console (turn down all faders, auxilary sends, reset all EQ controls, and set all switches to their standard position).


Baffling The Amp

When your amp is in a live-sounding small, or medium-size room along with mikes for other instruments, leakage from one track to another can occur. Leakage will be a major problem if you need to fix a performance later, because when you punch in, the leakage disappears and the mix changes. Baffling ( surrounding the the amp with sound-absorbent structures ) can minimize leakage.
If necessary, create a baffle box. Pro studios use manufactured baffles that combine air pockets and sound-absorbing materials. However, you can stack milk crates and throw blankets over them, or get two tall fans and have them stretch a thick blanket between them. All baffle surfaces should be very soft, for example, cloth stuffed with cotton. Baffle each side of the amp ( unless you're using a closed-back cabinet, in which case the baffles can form a V in front ), with a baffle lying across the box's top. If you don't have a good baffle for the top, use a packing blanket. Leave space on the front for speaker "breathing room" as well as space for the mike stand. All other sides can be baffled "tight". If the room has a soft, non-reflective wall, point the cabinet toward it and use the wall as a baffle too. Angle the speaker slightly away from the wall to avoid phase problems.
Caution: When baffling overhead with combo amps, allow for air to prevent the amp from overheating. Never let a blanket drape over the back of the amp ! With a separate head and cabinet, set the amp head on a carpeted section of the floor, so the speakers wont rattle the the electronics. As always, patch the amp to the cabinet with heavy-duty speaker cables, preferably 14 gauge or heavier, NOT mike or guitar cables.

Refining The Sound

Once the baffling is set, and the mike is roughly in place, dial in the sound on the console. First, set the levels to avoidoverload. Next, move the mike to find the best spot. Before adding console EQ, try adjusting the tone at the amp (read more about equalization in the next page), when it sounds good, try adding some console EQ.
If the sound still isn't right, you may need to move the mike around some more. If that helps, switch out the EQ and start over.
Try other mike's, too. You often won't get things right the first time, so don't be impatient.
Even with really good miking, you may notice certain notes jumping out or droping back in level. This is normal and caused by frequency buildups and cancelations. Adding compression should help (read more about the art of compression in the compression page).
When the amp is isolated in its own room, adding a room mike can yield a more live, rock-friendly sound. Place it a fair distance from the amp so it will pick up a lot of room reflections. There may be huge anomalies in the low end, so you may need to add lots of compression and EQ before it blends with the other bass signals.

 

Next; Equalization