If you'd like to breathe some life into your acoustic drum recordings, here's what you need to know.
Most musical instruments are relatively straightforward to record in isolation, but the drum kit is actually an ensemble of instruments, and so can present more of a challenge. Furthermore, in pop music, the result that we strive to achieve is often not the most natural sound possible but the most musically useful one. The recorded sound of the kit is also very dependent on the way the kit is tuned and the acoustic environment in which it is played, not to mention the way in which it is played, and that's before you start to take into account such variables as microphone types, microphone positions and the use of processing such as EQ, compression and artificial reverberation.
For the sake of this article, I'm going to start from the assumption that the drum kit is well-maintained and well-tuned — which is something that you can't always take for granted. If you are unsure how to tune a drum kit, it may be worth paying for a lesson or two with a good drum teacher. Its a really valuable skill to learn, even if you're never going to be the one playing the drums. For a given depth and diameter, a drum has a very definite range of pitches over which it sounds good. If you tune the drums too high or too low, the sound will be compromised. You'll also learn about the differences in sound that are achieved through using different types of drum heads, which are designed with varying degrees of inherent damping. As a rule, simple coated heads (usually with a matt white surface) have the most lively tone, at the expense of depth, whereas double-layer heads, with an oil film between the layers, are the most heavily damped. A common compromise is the Remo Pinstripe head, which is easy to recognise as it is transparent and has a black ring around its perimeter an inch or so away from the edge. Further damping can be applied using small pads of fabric or tissue held in place with Gaffa tape, or you can opt for one of the more modern solutions that take the form of tacky gel pads that stick to the drum heads.
The various methods of miking a drum kit have been covered in Sound On Sound on many occasions, so I'll stick to the basics here. At the simplest level you can get away with a kick-drum mic plus a single overhead to pick up the rest of the kit, but the simpler the approach you use, the more the acoustic properties of the room tend to affect the sound and the less control you have over the balance of the individual drums. In a great-sounding room, you could even get away with a single mic placed a few feet in front of the drum kit, but in a typical home studio, where the acoustics tend to be less than optimal, this seldom yields great results.
It is probably true to say that the majority of studio drum recordings made today use close mics on every drum, plus a stereo pair of overhead mics to pick up the overall kit sound, and to bring out the cymbals. There may also be a separate hi-hat mic, and in studios that have a lot of space, there may be a further stereo pair out in the room to pick up the room ambience. There are variations on this approach, but in the main that's the way it is done. The close mics pick up the drum closest to them, plus some spill from the other drums and cymbals, but the level of room reverb they pick up is relatively low, simply because they are so close to the drum head. A typical setup places the mic no more than a couple of inches from the drum head and around the same distance from the edge of the drum, but you should experiment with the position as much as is practical, as varying the mic placement will change the sound just as it would for any other instrument. It is also common practice to use cardioid-pattern mics for close-up work, and to arrange their angles in such a way as to minimise spill from the other drums, though spill is impossible to get rid of completely. Other than the hi-hat mic, which should ideally be a capacitor model, so as to more faithfully capture the high-end, the close drum mics are often dynamic cardioids, though some engineers prefer the better-defined sound of capacitor models for all the drums, and some choose omni-pattern mics rather than cardioids. Omnis may seem like an odd choice, but their off-axis response is more accurate than that of cardioids, so although they tend to pick up more spill, what they pick up will sound more accurate. Consequently, you may be able to accept a higher level of spill.
Recently we've seen the introduction of affordable drum-mic kits using dynamic or back-electret capsules, and in some cases the mics have an integral clamp system that eliminates the need for stands, other than for the kick-drum mic and the overheads. Even the less costly of these can produce surprisingly good results, but if you're serious about getting a good sound, it's best to avoid the entry-level models and pay a little more for something with a better specification.
For overheads, you can use any stereo mic configuration you like. Spaced cardioids or coincident cardioids are popular choices, though omnis probably give the best results in a sympathetic-sounding room. Because cymbals can generate very high audio frequencies, capacitor microphones are the most common choice, though some engineers like the softer sound of certain ribbon models in this role. As a rule, the overheads would be positioned at least an arm's length above the highest cymbal, but I'll be looking at some alternative strategies for use in smaller rooms or rooms with low ceilings. A useful tip when using spaced overheads is to ensure that they are both the same distance from the snare drum, so as to prevent the snare sound being affected by tonal changes due to phase cancellation if the recording is replayed in mono.
When miking the kick drum, the most common approach for rock or pop recording is to either cut a hole in the front head, or to remove the front head altogether, to allow the mic to be positioned inside the drum shell. The mic must have a good low-frequency response, and there are dedicated kick-drum mics on the market that have tailored frequency response curves to accentuate the 70-90Hz thump, as well as the 2-4kHz beater click, but with a dip in between to keep the mid-range clean. The AKG D112 is probably the best known of these, but if you already have a microphone that has a good low-end response (and that can handle the high SPLs encountered inside a kick drum), there is a device made by Earthworks called the Kickpad, which is simply an in-line passive filter that both attenuates the output from the microphone and equalises it to conform to the above description of a tailored kick-mic response.
Unlike the other close drum mics, the kick mic seldom gives good results if positioned too close to the batter head (the one being hit by the beater) and a common starting point is to put the mic mid-way between the centre and the edge of the drum shell, protruding into the shell by just a few inches. You can then make a test recording and move the mic if necessary. Damping is usually provided by a folded blanket in the bottom of the drum shell, and as with the other drums, tuning and choice of head have a big influence on the sound, as does the choice of beater material (wood, plastic, felt, cork and so on). Where you need to coax a better-defined beater click out of the drum, taping a plastic card to the outside of the head, just where the beater hits, can help give you more of a slap.
In an ideal world, you'd put up your carefully selected mics around a fabulous-sounding drum kit in a great-sounding room, and capture your dream sound with little or no further processing. In the rather more realistic world of the home studio, it is more likely that you put up your affordable mics around a drum kit that you've done your best with and then scratch your head when you hear how it really sounds once recorded. Providing the kit is tuned reasonably well, the close mics should pick up a decent sound, though in my experience a snare drum miked only from the top often sounds rather dull, before you add the contribution of the overheads. You can get a bit more snap by putting another mic under the snare drum (but remember to reverse the phase of this mic, either when recording or mixing, as it is pointing in the opposite direction to the top mic), but this is by no means essential.
Where a small room really starts to get in the way of a good sound becomes evident when you solo the overhead mics. These are far enough away from the kit to pick up room ambience and, as a result, you often get a boxy, congested sound that is hard (if not impossible) to fix using EQ or other processing. What's more, if you decide to compress the overhead sound (or the complete drum mix), the room character will become even more pronounced. In a good-sounding room this can work, but in a typical domestic room it is just one more problem to overcome.
My preferred strategy these days is to record in a good-sounding room if I can. Where this is not possible, I'll use whatever acoustic treatment I can improvise to keep room reflections out of the overhead mics. This gives me the opportunity to use artificial reverb to create the impression of the kit being played in a better-sounding room — and some of the convolution-based reverbs can do this very convincingly. If the overheads are hanging above the kit in their usual places, the biggest problem is from ceiling reflections, as this is the closest reflective surface. Placing a barrier of acoustic absorbing material between the back of the mics and the ceiling can really help. There are commercial screens that can work well here, the simplest being small foam panels and the most elaborate being multi-layer devices, such as the SE Reflexion Filter, and its smaller instrument counterparts. You can also dream up ways of suspending conventional acoustic foam panels, or even blankets and duvets, over the kit and, where practical, fixing thick foam panels directly to the ceiling can help.
While cardioid-pattern mics are considered to be unidirectional, they are in reality anything but. They're pretty 'deaf' directly behind, but the sides of the mic are still very sensitive, which is why it is a good idea to get a barrier between the mics and the ceiling, as discussed above. You also need to think about reflections from walls. Where possible, avoid having the drum kit too close to the walls. You can dry up the sound considerably by hanging some duvets behind and to the sides of the kit: boom mic-stands set up in a 'T' shape make useful supports for temporary duvet screens, and where ceiling height prevents you getting good results from the overhead mics, try dropping them to cymbal level or just above, and moving them two or three feet in front of the kit, looking back at it.
Timing & Drum Replacement
While fixing timing problems isn't the main focus of this article, it is worth a mention, as small timing problems in the performance can distract from an otherwise great take. If you need to move a beat slightly to get it into time, make the edit across all the drum tracks, otherwise the spill into the other drum mics and overheads will still be audible in the original position. The safest way to do this without getting into a mess is to group the drum tracks so that all the parts remain in sync when you make an edit, then work on the Arrange page of your sequencer, zoomed in so that individual beats are visible. Often you can cut either side of the beat you need to move, then slide it to its new position. More often than not, the added reverb will cover any slight discontinuity caused by the edit. You may also be able to find a better bar elsewhere in the song and copy it to replace a bad one, though if the song is played without a click track, the tempo needs to be reasonably constant to let you get away with this. If you are working to a click and your sequencer has an audio quantise feature, this may get you out of trouble, but don't bet on it: I often find that manual edits work best.
Of course, there is specialist software available for improving the timing of drum tracks, and for replacing individual drums sounds with samples, but that's a different article (if you are interested, Matt Houghton's Cubase technique column in SOS May 2007 covers some of this ground). Logic users with no additional drum-processing software often find the 'Audio to Score' facility useful for turning drum hits into MIDI data, though you need to run a transform (Transpose / fixed note) afterwards to move all the resulting MIDI notes to the value required to trigger your samples. This feature works using a threshold setting above which detected notes are deemed as real, so the better the separation you have between drums, the more accurate the result is likely to be. If you don't have Logic, you can get similar results from other audio-to-MIDI software, such as Melodyne.
Putting It All Together
Though it is worth trying to improve the sound of the individual close mics using EQ or other processing, you shouldn't spend too long doing this in isolation from the rest of the kit, as the sound will change when the overhead mics are brought into the mix. In fact, the overhead mics are generally used to contribute the main part of the drum mix, with the close mics just being added to balance the kit and to provide a bit more tonal depth. That's why it's vital to achieve the best overhead sound you can, and why, where the room isn't contributing anything useful to the sound, you need to exclude as much room ambience as possible. That way you can substitute a more suitable acoustic using artificial reverb. My current preference is to use a convolution reverb, loaded with an impulse response taken from a nice drum room, but it will only sound convincing if you've minimised the ambience of the room you actually recorded the kit in.
As the close mics provide a lot of depth and punch, you can often afford to roll some low end out of the overhead mics to thin out their contribution to the sound. A side-benefit of doing this is that you also reduce the boxy coloration caused by any remaining room ambience. A broad EQ boost centred at around 10kHz will add definition and sparkle to the cymbals if required, and you can also roll off some low end from the reverb if you think the sound is getting too muddy.
When it comes to treating the close mics, there are various tricks for improving the sound, including the use of compression, though some engineers prefer instead to compress the entire stereo kit mix. If you have the time, try both approaches and see which you prefer. As a general rule, compressing the close mics will help you deliver a punchy, even sound, without making the result seem too processed, whereas compressing the overheads or the complete kit can cause the drum levels to modulate the cymbal levels in an audible way. The latter approach is often used deliberately to create an exciting rock sound, but it less appropriate where you want the drums to sound natural.
Kick-ass Kick Drums
Kick drums are loud and therefore tend to overpower any spill by a reasonable margin, making it easy to set up a gate to kill the spill or to shorten the decay time. You should use a fast attack time, with a release setting that is long enough to allow the drum sound to decay naturally. If you have side-chain filters, you can use these to reduce the risk of false triggering by setting the upper filter to 2-3kHz. This will reduce the level of snare drum and cymbals getting into the gate's side-chain detector circuits.
If the kick needs more low-end weight, you can EQ it after gating it, by applying some boost in the 70-90Hz region, but you may also find that cutting in the 150-200Hz region reduces any tendency for the kick drum to sound boxy once the low boost is added. If you need more attack, some 3-4kHz boost may help, but where there is insufficient high end there to boost, I have occasionally resorted to using harmonic exciter plug-ins to synthesize a little more high end. This approach can work well, as long as you are careful to adjust the exciter's tune control so that what is added compliments the sound you already have.
Should you feel the need to compress the kick drum, it is often appropriate to put the compressor before any equalisation you might apply and to set an attack time of around 5-10ms, as this helps emphasise the attack of the sound. A release time of 50-70ms will allow the compressor to reset before the next beat comes along, and with a ratio of around 5:1 you can adjust the threshold control, so that the loudest hits register in the region of 6dB of gain reduction on the gain-reduction meter. However, drum sounds are subjective, so it's worth experimenting with the processing chain: try the compressor after the EQ, rather than before, to see what difference that makes. As a rule the compressor will react more strongly to those parts of the spectrum that have been boosted when it is inserted post-EQ.
Snares With Snap
A side-effect of compression is that individual drum sounds may have more or less attack than they originally did. If you need to restore some bite to the sound, the classic tool is the SPL Transient Designer, though software equivalents such as Sonnox's Transient Modulator and Cubase 4's Enveloper can also work very well.
As mentioned earlier, the snare drum can sound dull in isolation, and if the sound is still too dull when you bring in the overhead mics, consider using that harmonic exciter plug-in again, in a fairly heavy-handed way: this trick often works well. Initially, turn up the level of excitement to near maximum, then adjust the tune control until what is being added sounds snappy and crisp. Once you've located the best tune setting, you can then back off the amount added until the snare sound comes across as more natural. If you detect boxy overtones, you can try sweeping an EQ between 150 and 300Hz on full boost to find the offending frequency, then applying cut at that frequency to clean up the sound. SPL's Vitalizer also works well on snare drums, as does Noveltech's Character plug-in.
Hi-hats & Toms
Though I rarely use separate hi-hat mics, when they are necessary it helps if you cut out as much low end as you can without affecting the subjective tone, as this reduces the effect of spill and cleans the sound up to a useful degree. More brilliance can be added using a (now familiar) 10-12kHz broad boost, while harshness can be reduced by cutting in the 3-6kHz region where cymbals tend to be at their most brash.
Toms often require the least processing but gating is almost a prerequisite, especially with double-headed toms, as they tend to ring every time one of the other drums is hit. Where the tom parts aren't too busy, it may be easier to use your waveform editor to silence any unwanted sections between tom hits — and if you physically remove silenced sections from the Arrange page, you'll also reduce the processor load, as the system will no longer be reading stretches of silence from the drive between tom fills. If you need to apply EQ or compression, make sure you evaluate the effect with the overhead mics mixed in, as these tend to have a very significant effect on the tom sound.
Compression & Reverb
Using compressors, you can give your individual drum sounds more or less attack but that relies on careful adjustment of the compressor attack times, and the effect is level-dependent, so it may only work on the louder hits. SPL's Transient Designer makes this much simpler, as it is essentially level independent and has just two knobs to control the attack and decay of the drum sound. At the time of writing this is not available as a native plug-in (though there is one available for users of Creamware's Scope DSP system). The nearest native software equivalents include Sonnox's (formerly Sony) Transient Modulator, Waves' Trans-X and the Enveloper plug-in included with Cubase 4.
Having stripped away all the undesirable room acoustics, it will be necessary to add some synthetic reverberation to prevent the kit sound being unnaturally dry. Often you'll only need to add this to the overhead mics to get a natural sound, but for a big rock snare you may want to add some additional plate-style reverb to the snare. If the low end of the reverb seems too busy, roll off the reverb below 200Hz or so, and if you're after a lively but not obviously reverberant sound for the kit, choose a small, bright room ambience treatment. Though convolution reverbs are the most realistic-sounding, a synthetic ambience treatment can be equally effective from an artistic perspective.
If the overall kit sound is too dull for your taste, first try adding 12kHz 'air' EQ to the overhead mics. If that doesn't do the trick, consider gentle overall top-end enhancement, again using either a conventional harmonic exciter or something like Noveltech's Character over the whole drum mix. You may also find that dipping the low mid in the 200-500Hz region cleans up the kit sound, but it helps to keep checking the sound against a good-sounding commercial record, as it is very easy to get carried away and apply too much processing. Where the overall kit sound ends up being too abrasive, using a tube simulator, or even running the drum mix through a hardware tube preamp, can sweeten the high end. Traditional rock producers swear by recording to analogue tape, as the soft saturation helps create a dense and punchy drum sound. This is worth trying, but as few people now work with tape, tube gear or plug-ins that simulate either tube or tape saturation make a good substitute and can really help beef up the sound. I like to use PSP's Vintage Warmer plug-in for sweetening drums, as it combines variable saturation with compression, EQ and limiting.
Overall compression can also help deliver a more solid kit sound. A slower attack time (10-30ms) will allow the transients to come through with maximum definition. The faster the release time, the more audible pumping is likely to be when you apply a lot of gain reduction, but there's no hard and fast rule here as much depends on the sound you want and on the amount of gain reduction being applied. The best approach is usually to reduce the release time until the gain pumping becomes too noticeable, then increase it again, but only slightly.
Analogue tape saturation can have a very pleasing effect on rock drum sounds. If you don't have access to tape, you can opt to use a plug-in such as PSP's Vintage Warmer, which can impart some of the same sort of character.
No article on drum mixing would be complete without a word about panning. Try to avoid panning the kit too widely, as it makes the drum kit sound as wide as the rest of the band. How far you pan the overheads depends on the original mic spacing and mic characteristics, but your ears will tell you when the result sounds realistic. You should then pan the tom mics to match their apparent positions in the overheads, leaving the kick and snare in the centre. Drum panning is generally done from the perspective of the audience, which places the hi-hat on the right of a kit played by a right-handed drummer.
Achieving a good drum sound relies on attention to detail at all stages of recording and mixing, not to mention the tuning and playing of the kit. However, creating your own recorded drum sound can be much more satisfying than relying on samples, and you'll certainly learn a lot from doing it. Because there are so many variables, every drum recording is unique, but keep in mind that it is how the drum kit sounds in the track that really matters, not what it sounds like when solo'd. For this reason, any overall kit processing is best finished when you have the whole of your mix running.