Thursday, December 29, 2011

Engineering Drums Part Nine: Room / Ambient Mics

In the 1970's recording studios were most often very dead rooms with thick carpet, sometimes on the walls and ceilings, and plenty of fiberglass absorption to go around.  Dead, dead DEAD!  Drums were rarely ever given reverb for processing, and for the most part the drum sound you got from the close mics, with the exception of some gating, was the sound that made it into the final mix.

In the 1980's, of course, digital reverb became viable, and many models proliferated the market (and our eardrums) throughout the decade.  In an effort to add space to those dry, 8-bit and 12-bit samples from a LinnDrum or an Akai S900 sampler engineers lathered on liberal amounts of digital reverb, and it was cool!

And then it wasn't.

In general, truly dry drum sounds are a thing of the past.  While it's common to have drums that don't sound overtly ambient there is almost always some essential spatial information mixed it to put the drums in an appropriate environment for the rest of the mix, even if the ambiance is subtle enough not to pull your attention.  Most often this ambiance is provided not by an reverb algorithm crunching numbers, but by mics, well chosen and placed to pick up the sound of the room while tracking drums.

Room or ambient mics capture the environmental response to a drum kit, not so much the kit itself (you've got close mics for that).  The close mics don't pick up much room sound at all.  If you use omnidirectional mics overhead, and place them high above the kit, then you're likely to capture greater room content, but still it's nothing like a mic or two placed 10 feet away from the kit.

I've seen all kinds of mics used as room mics with excellent results.  Condensers will give tremendous detail to the environment, while ribbons will capture a smooth, yet natural perspective.  I've also had excellent results with a pair of Shure SM57's, spaced 5-10 feet apart, pointed directly at an opposing wall, about a half-inch off the wall.  The Shures had less detail in them than a condenser placed out in the room, but the sound was dark, natural, and ambient.

The microphone/room combination is literally endless -- some rooms are well-designed acoustic spaces with quick, smooth decay and no standing waves.  Put up a couple of gorgeous large-diaphragm condensers and you're good to go.  Other rooms, with their rectangular design and plaster walls, are meant for watching TV, not recording.  Here standing waves abound, as does a rather unpleasant mid-range content.  A microphone with a darker personality is the more appropriate choice for capturing this room, and with a placement position and angle to minimize the standing waves.

Rather than try to recommend what kind of mics and placement to use for your room I think it will be more helpful to give a few pointers and then tell you to trust your own ears.   

Pointer Number One:  Listen, listen, listen!  

It is always a good idea to first listen to an instrument you're about to record before choosing and placing a microphone.  This is especially true when trying to capture the sound of the environment around a drum set.  Even without listening you can have decent success miking an acoustic guitar with a small diaphragm condenser about a foot off the instrument, pointed at the 12th fret.  Perhaps not the best placement for a given instrument and player, but most likely a solidly useable signal.  But when trying to mic room there is no similar basic placement.  Each room is vastly different.  You absolutely must go out there and walk around the room while the drummer plays.  

Squat down low to the ground and then stand up straight.  Walk in front of the kit and behind, close and farther back.  Listen for an area with a good balance of drumkit elements and ambient information with no standing waves.  If you've got only one mic for rooms, place it here.  If you have a pair, space them a few feet apart, centered on this spot.   

Pointer Number Two:  If your room is a 'shoebox' (a rectangular room with parallel walls) try positioning the drums off center toward a corner and facing into the corner diagonally across the room.  This will help minimize standing waves between parallel surfaces.  

Also, try to break up the room acoustically and give it some diffusion by positioning large objects (furniture, shelves, etc.) strategically to break up the more obvious standing waves, giving the room a more natural decay.  You could also hang a curtain at one end of the room, or bring in some 4'x8' sheets of plywood from your local home improvement store to position around the room to further diffuse the reflections.  The more diffuse your room, the more complimentary it will sound when layered with the close mics of the kit. 

Pointer Number Three:  If you find that the room has an annoying midrange 'honkiness' to it (often accentuated by the snare drum), then snag a few cheap bed pillows ($3-$5 at the Mart of Wal), and nail them up in corners of the room (ceiling corners, not floor corners), particularly the corners closest to the drum kit.  Hi frequencies are absorbed by air over distance, and low frequencies tend to go right through most walls (which is why all you hear of the stereo in your neighbor's apartment are the low frequencies), but mid frequencies, while strong enough to not be easily absorbed by air, aren't strong enough to penetrate plaster walls and are reflected instead.  Corners at the top of the room are major culprits in focusing these frequencies from three converging surfaces into offensive, resonant sound.  Just one pillow each in a couple of these corners will dramatically reduce this offensive information and make your room much more pleasant and musical. 

Pointer Number Four:  For sparse mixes where the space around the drums will have greater importance (an acoustic jazz trio, for example) use mics with greater resolution -- condenser mics.  The smaller the diaphragm the lower the mass, the greater the resolution.  Uber tiny diaphragm models from Avenson Audio and Earthworks, with their incredibly fast impulse response, will give you the feeling of 'being there,' while large diaphragm models will have excellent resolution, but a more studio or "hi-fi" character.

Low-mass ribbon designs work well here too, though they tend to be more expensive.  Most ribbon mics use 2.5-micron or thicker ribbon material.  Commonly-available Chinese ribbons can go up to 4 microns, and these are often paired with a cheap output transformer that further blurs the signal.  While these mics can be useful for heavier productions I find their overall murkiness unsatisfying for more articulate duties.  The one ribbon model that I would consider truly hi-resolution is the classic BBC design now sold as the Coles 4038.  Owing in no small part to the ultra low-mass of its 0.6-micron ribbon (which is not only a fraction the thickness of most ribbons, but is also cut to roughly half the length of most others ribbons as well) the 4038 provides a smooth, yet defined and articulate perspective of whatever it's pointed at.  I love them on just about anything.  At a bit over $1k each they aren't cheap, but they're lovely! 

Pointer Number Five:  For denser pop/rock productions, pretty much anything goes in the room mic department.  Condensers, Chinese ribbons, classic Coles, RCA and Beyer ribbons, and dynamic mics of all makes and models.  The mic that works for your room is the mic to use.  

I personally hate the overused "if it sounds good it is good" statement, bus alas, it's true.  Remember, room mics provide additional content to augment the close mics on the kit.  The clarity of each drum in the kit will come from the close mics.  The room mics only provide a sense of space to support the close sound, and the room you're miking will dictate what works and what doesn't.  There's lots of 'room' for you to experiment! 

Pointer Number Six:  If using mics with a directional characteristic, compare the sound of the mics pointed directly at the drums with the sound created by positioning the mics with their null points facing the drums (effectively removing the 'direct' signal from the mic).  If the mics are cardioid, point them at the kit and then point them the other way.  If the mics are figure-8 (like the Coles) then its greatest null will be with the mic positioned 90-degress off axis from the source.  Pick whichever placement sounds better to you (I've had great success with both approaches).  

Pointer Number Seven:  Use the room mics sparingly.  This is obviously a preferential call, but take care with levels to ensure that the room mics play a supporting role in the drum sound rather than fight the direct signals in any way.   

Trust your ears.

Next:  Processing!...

Monday, December 12, 2011

Engineering Drums Part Eight: Toms

When comes to miking toms I really do prefer to keep things simple.  I use one microphone per tom.  I know of folks who like to mic top and bottom, and doing so can definitely help with LF response, particularly on larger drums.  But doing so also requires not only more mics, stands, cables, and preamps, it also dramatically increases the trickiness of getting proper balance between all the pieces of the kit, minimizing leakage, etc.  I really do like to keep it simple.  While I would argue that two mics on the snare and kick are so useful as to be almost necessary, my experience with double miking toms (and my experience mixing tracks that were engineered by someone else using two mics per tom) has taught me that the potential benefits of using two mics on each tom is rarely worth the hassle and expense (time is money!).

So a quick discussion of mics:  I prefer a good cardioid dynamic mic for tom duties.  Floor toms, with their greater LF content (compared to smaller toms) benefit from a dynamic with extended LF response.  Most good quality dynamics will work fine, but the models more commonly used on toms include Sennheiser's MD421 and E604, Shure SM57, Beta 56 and Beta 57, Audio-Technica ATM23HE (for smaller toms) and ATM25 (a personal fav! See pics), Audix D2 and D4, and EV's N/D 408/468.  I also enjoy BeyerDynamic's classic M88 on floor toms (great kick mic too!).

Condenser mics are also used, at times, for toms, but because of their increased sensitivity they are prone to greater leakage issues than a good dynamic, and there's also the chance that damage could occur via an errant drumstick, which most dynamic mics will easily shrug off without a second thought.

So let's start with rack toms (smaller toms):  Begin by placing the mic about an inch or two off the top head with the tip of the mic just over the edge of the rim, pointed toward the center of the head.  This is usually a good starting point for a well tuned drum providing a nice blend of attack and resonance.  With the mic pointed at the center of the drum you'll get more focus on the fundamental with fewer overtones.  If you want more overtones point the mic more toward the edge of the head.

If the sound has too much attack and not enough body, move the mic in closer to the head.  Be careful not to confuse proximity effect (the artificially increased LF content produced by a closely placed cardioid mic) with the actual tone of the drum.  You may desire lots of LF in the sound, but if you get the mic too close you'll likely discover, once the drum is placed in a mix with other instruments, that it comes across as all mud and no articulation.

Here are a couple of pics of an Audio-Technica ATM25 on a 12" rack tom. 

Note the distance from the tip of the mic to the drum head.  Also note that the mic is pointed toward the center of the drum.  With this drum (single ply heads) this mic and placement provided a clear attack with defined, punchy tone that was fast and full.

I often see younger engineers positioning tom mics with the front almost touching the drum head.  Doing so creates a muddy sound that needs to be filtered to fit the overall presentation of the drum set.  Instead, let the drum breath a bit by backing the mic off an inch or two.  The point here is not so much about isolating the drum (though I will be using editing and processing to do just that in an upcoming article), rather, the purpose of this placement is to capture the overall natural character of the drum to provide the tone and definition missing from the overhead perspective of that drum.

If you later decide to make the toms sound dry and in-your face, this approach will give you the ability to do that.  If your placement is too close, however, and you later decide you want to lighten things up and make them more natural, you will likely find that harder to accomplish.

With floor toms (or larger toms) I recommend the same starting approach as I did for smaller toms, that is, the mic a couple of inches off the top head pointed at the center of the head with the tip of the mic directly above the rim.  The only real difference between floor toms and smaller rack toms is that the off-center approach (with the mic pointed more toward the edge) is almost never flattering to a floor tom.

Larger toms resonate more than smaller toms do.  Period.  As a result, even with the mic pointed at the center of the drum you will likely capture all the sustain you will ever need.  Pointing the mic toward the edge will, indeed, give you greater sustain with more overtones, but it will almost certainly be an overly resonant sound that will require editing and/or greater processing to bring under control.

I recommend you just point the mic at the center, and leave it.

You can still move the mic closer if you need more body, or further back if you desire to control it.

Here's an Audio-Technica ATM25 on a 16" floor tom:

This floor tom has plenty of resonance.  Like the heads on the rack tom these were single ply, so there was plenty of sustain and tone to spare.  You can see a strip of duct tape and a spot of moon gel on it to help contain the overtones a bit.  The sound was big and full, with excellent articulation.

When you have the toms miked, have the drummer hit quarter notes going back and forth between (or around) all the toms at a tempo that let's you hear the majority of sustain on each drum.  Listen for inconsistencies between each tom, that is, one may feel very short and punchy, with little or no 'bend' in the pitch, while others might have much longer decay and a strong bend to its pitch.  The  pitch bend issue can be addressed with tuning, but tweak mic placement as needed to get a fairly consistent attack-to-tone ratio from drum to drum.  This makes all the toms similar in character, so that they sound like they belong together on the set.  There can be musical reasons to not have the toms share a similar tonality, of course, but in general matching their tone through thoughtful mic selection and placement makes the drum sound more cohesive.

Once you're pleased with the sound, audition the toms again while bringing up the overheads to see if the image captured by the overheads compliments your close miked tom sound.  If all is well, the overhead perspective will blend with the focus and definition of the close mics to create a natural soundscape that makes the perspective of the toms dimensional and complete.  

That's about all there is to it with toms.  Pretty straight forward stuff, but again, trust your ears.

Friday, December 2, 2011

Engineering Drums Part Seven: Overheads

While the kick and snare microphones carry the bulk of the responsibility in pop music mixes, the overall image and presence of the drum kit is defined by the overhead microphones. Not only do the overhead mics pick up the cymbals, they also pick up different perspectives of the snare and toms – even the kick.  These mics, however, are many times the distance from each drum than that drum's own mic, so any potential phase issues are eliminated, that is, the distant sound of the drums as captured by the overhead mics is so radically different in content than the sound picked up by the close mics that when combined the two compliment rather than fight one another.  

Overheads often help to define the sense of space around the kit as well, particularly if the drums are being tracked in an ambient room.

In a very real sense the sound of the kit picked up by the overheads is the glue that make all the various elements of the kit belong together in the mix.  It is for this reason that we don't try to isolate the cymbals from the kit (which I strongly discouraged in Part Three). 

Overwhelmingly, condenser mics are chosen for overheads. Condensers reproduce high frequencies and intimate detail better than other types of mics. Both small and large diaphragm condensers are commonly used.  Small diaphragm models have a faster impulse response that sounds truer to life, while large diaphragms, with their greater mass, tend to produce a sound that is smoother and bigger.

Let's talk briefly about polar patterns.  By far the most common pattern used for miking drums is cardioid.  The directionality of the cardioid pattern makes it a good choice for better isolation when using so many mics in such a small area.  When used for overheads cardioid mics give the engineer the ability to create a dramatic stereo image of the drumkit.

The omnidirectional pattern, by contrast, doesn't discriminate against sound coming from any particular direction, but rather, picks up all sound, regardless of where it's coming from. A pair of omnis, a couple of feet off the cymbals and spaced a few feet apart can yield an incredibly natural stereo image (which I personally enjoy), but this arrangement will also pick up more of the room the drums are in than a cardioid pair will. Because they don't reject sound from any particular direction, omnis hear much more of the environment around the drums, so while they can produce wonderful results, they also require a bit more effort to capture the balance you want.

Let's start with cardioids. For a good balance place the mics a couple of feet above the cymbals, one on each side of the kit, separated 4-5 feet, pointing essentially straight down. The spacing of this approach, coupled with the directional characteristics of the mics creates a sufficiently wide, yet natural image of the overall kit.

To ensure a solid snare drum image take care to position the diaphragms of both mics the same distance from the center of the snare drum head. The snare is arguably the most critical drum on the set, and is clearly captured by the overheads. With the overhead mics equidistant from the snare, the snare sound will arrive at each mic simultaneously which will avoid the head-spinning phasiness that can easily occur when the mics are unequally placed. Because the snare drum is to the side of the kick drum spacing the overheads equidistant from its center usually means one of the mics will be placed higher off the ground than another (assuming you keep the mics directly over the cymbals). Don't let this concern you.

For greater stereo separation angle the mics away from each other toward the outer edge of the kit. For less separation bring the mics physically closer together, remembering to keep their spacing equidistant from the center of the snare drum.

Another common approach for overhead placement, which provides a more natural, subtle stereo image is to center a pair of cardioid condensers over the kit, with their capsules almost touching, pointed 45-55 degrees off axis (for a total angle of about 90-110 degrees) toward the edges of the kit. Because the mics are so close together the sound of everything on the kit practically hits each mic at the same time, eliminating phasing for just about every part of the kit, and the directionality of the mics provides the separation. Off-axis coloration from each mic blends the middle information smoothly, creating a more natural perspective.

If you want more sound from the room you can switch to omnidirectional mics, or you can raise cardioid mics higher into the air, providing more space for room reflections in the sound.

Hi-hats will often get their own mic, usually a cardioid condenser, placed about a foot off the top of the pair. Point the mic toward the center of the top cymbal for a more focused sound, and toward the edge for a more aggressive character. Place the mic in such a way as to point away from the kit, while pointing at the hi-hats. This will help isolate the hats from the rest of the kit.

On occasion the ride cymbal will also gets its own mic, also a cardioid condenser, placed similarly as the hi-hat mic, or, occasionally, underneath the ride. The 3-to-1 rule applies here, that is, the overhead mics should be at least 3 times as far from the ride as the ride mic to avoid phasing when the ride is played. Take care not to place it too close to the ride. Most rides are large and heavy and create a great deal of hummmmm..... so stay far enough away to keep it sounding like a proper ride cymbal.

By miking hi-hats and rides separately it gives the mix engineer more control over the definition of these time-keeping elements in the groove.

Next the toms, and then on to processing.....

Thanks for reading.