One of the foremost objectives during the recording process should be to record instruments in such a way that as many creative options as possible remain open at the mixdown stage, so that artistic decisions can still be made at that point. To achieve this in the case of the drum kit, it's desirable to maximise separation between signals from different instruments or sections of the kit. This is best achieved by spreading the drums across as many tracks as possible on the multitrack. In practice, of course, one must strike a compromise.
When working on 24-track I generally record the bass drum, snare drum and hi-hat on separate tracks, with a stereo pair for the toms and another pair for the overheads. This method is too extravagant for 8-track or 16-track recording, and when I'm constrained by the number of available tracks my first instinct is to combine the toms and overheads onto a single pair of tracks. After that, I would consider combining the hi-hat signal into the toms/overheads stereo mix, retaining just the snare and bass drum on separate tracks, but it's prudent to consider how the drums will be mixed in the context of the type of music you are recording, and keep separate those which are most important, or to which you're most likely to want to apply special effects and EQ.
The bass drum and snare drum, and to a lesser extent the hi-hat, form the heart of the drum kit, and it is often desirable to treat them individually during mixdown. I try to keep the bass drum separate if at all possible, even when working with only eight tracks. Where extra percussion instruments are used, they can often be fitted into gaps on other tracks -- the hi-hat, for example, is unlikely to be used at the same time as a cow bell, so it would be appropriate to assign both to the same track.
Percussive sounds start with an extremely sharp transient, and decay rapidly, so the peak level of a signal from a percussion instrument is very much higher than the RMS (average) level. As a consequence, the same percussion signal will register a much lower level on a VU meter, which displays the average level
Analogue tape is quite forgiving of transient overload -- indeed, just before the onset of clipping, which takes place when the tape is magnetically saturated, there is a stage where the tape behaves in a non-linear fashion and 'tape compression' occurs. This effect can be used creatively because it will often thicken up the sound of the bass or snare drum. However, caution must be exercised to make sure that the tape is not driven too far into saturation, as this results in a clipped, distorted sound.
Digital recorders, whether tape- or disk-based, must be used within their headroom, as any overloading will result in clipping, producing a harsh, granular sound that cannot be salvaged.
MIXING: STEREO IMAGE
The first step in setting up the mix is to pan the signals so that a realistic stereo image is created. Bring up the overheads first, and pan them left and right sufficiently to produce a realistic stereo width. It's not advisable to pan them hard left and right, because this would fill the stereo image and give the implausible illusion of a 20 foot-wide drum kit! It's usual to pan the mics so that the kit is heard from the audience side, with the bass drum central and the hi-hat slightly to the right. The other drum tracks can then be brought up and panned individually. Bear in mind that the overhead mics will have picked up the sound of the whole kit, so these other drum tracks must be panned so that they occupy the same position in the stereo image as they do on the overheads. Careful listening and adjustments to pan positions will be rewarded by a realistic, three-dimensional drum sound with stable stereo imaging.
Once the drums are faded up and panned to the right positions, you can consider where corrective or creative effects, in the form of compression, gating, EQ and reverb, are required.
Compression serves a dual purpose when you're recording drums. It can be used firstly to even out the dynamic range of a signal, and secondly as a creative effect to alter the sound of the instrument.
The bass drum is the fundamental instrument in the kit, and it is imperative that it provides a steady, even beat. Compression is invariably used to help achieve this, by ironing out any inconsistencies in the SNARE DRUM TOM-TOMS HI-HAT
For a modern sound, boost slightly in the 6kHz to 12kHz region, to accentuate the transient click as the beater hits the skin. The thump of the beat can be brought out by boosting between 2kHz and 3kHz. To give a deep, powerful 'thud' to the sound, boost between 75Hz and 100Hz. If the sound has a tendency to boom or resonate, try cutting between 200Hz and 400Hz.
To accentuate the stick impact and rim shots, boost at about 5kHz. The rattle of the snares lies mostly between 5kHz and 10kHz. The 'bang' of the drum is in the region of 1-3kHz. The body resonance of the drum can be found at 100-250Hz.
The tom-tom sound can be made more dynamic by boosting at around 6-8kHz for the stick impact and 3kHz for the 'thwack'. The body of the sound generally lies between 100Hz and 500Hz depending on the size of the drum. Depending on context, you may wish to boost the lower registers to add power and coloration, or cut these frequencies to emphasise the impact rather than the body and decay of the sound.
The major components of the hi-hat sound are the ring, from 7-10kHz, the stick noise, at about 5kHz, and a clang in the region of 500Hz to 1kHz.
Most engineers encounter severe problems in achieving good separation between the hi-hat and other instruments: in fact it tends to bleed through onto virtually every microphone, no matter what efforts are made to reduce spill. A gate can be used where it is necessary to obtain greater separation between instruments -- for example, if you want to process or add an effect to a specific instrument. The gate is set so that it opens to let signal through as soon as the instrument is hit, and closes again when the sound has finished or died away.
Great care must be taken when setting up gates. In particular, the trigger level must be set so that the gate opens on every beat of the instrument being gated, but is not triggered by any of the instruments which are spilling over.
Setting the trigger level can be problematic. To return to the example of spillage from the hi-hat into the snare microphone, it will be often be found that the level of the spill is as high, or almost as high, as the level of the sound from the snare, so a way must be found to get the gate to trigger from the snare beats only. This can be accomplished either by using a gate with a side-chain filter, or by means of an external key input.
A gate operates by splitting the input signal into two parts, one of which is called the side-chain signal. This is used to control the opening and closing of the gate and operates in conjunction with the threshold, attack, hold and release controls. The threshold determines the level of input signal required to open the gate; the attack control adjusts the speed at which the gate opens once the threshold has been reached; If you don't have space to record a whole drum kit, and you're using programmed drums or a drum machine, you can get a much more realistic feel by programming the main kick/snare backbeat, then adding real cymbals, hi-hats and maybe tom fills. MIDI drums often sound better when played from pads by a real drummer, as quantising a keyed-in drum part usually kills the feel of the performance. Try heavy compression on the overhead mics only. This can really open up the room sound and adds a sense of life and power. If you use both close mics and overhead mics, the overall kit sound can be completely changed by varying the balance between the close mics and the overheads. If the room sounds too dead, set the kit up on a sheet of lino or a piece of board to reflect some sound. Digital reverb can then be used to fine-tune the ambience. A noise gate can be employed as an envelope shaper and used to tailor the attack and decay of a signal. Generally a very fast attack (opening) time should be selected when processing percussion instruments, so that the transient is not cut off.
Make the drum sound more interesting by using different reverb settings on different parts of the kit. Use longer decay times on crash and ride cymbals, and a shorter setting on the snare. Use reverb sparingly (or not at all) on the drums to avoid a boomy sound.
If you don't have space to record a whole drum kit, and you're using programmed drums or a drum machine, you can get a much more realistic feel by programming the main kick/snare backbeat, then adding real cymbals, hi-hats and maybe tom fills.
MIDI drums often sound better when played from pads by a real drummer, as quantising a keyed-in drum part usually kills the feel of the performance.
Try heavy compression on the overhead mics only. This can really open up the room sound and adds a sense of life and power.
If you use both close mics and overhead mics, the overall kit sound can be completely changed by varying the balance between the close mics and the overheads. If the room sounds too dead, set the kit up on a sheet of lino or a piece of board to reflect some sound. Digital reverb can then be used to fine-tune the ambience.
A noise gate can be employed as an envelope shaper and used to tailor the attack and decay of a signal. Generally a very fast attack (opening) time should be selected when processing percussion instruments, so that the transient is not cut off.
In our example the aim is to let through snare drum frequencies without allowing the hi-hat to open the gate. The filter must thus be set to let through a frequency band which is strong on the snare but weak on the hi-hat, such as frequencies below 3kHz. To do this, set the low-pass filter to this frequency. The hi-hat will not then trigger the gate, because most of its acoustic energy is above 5kHz.
Alternatively, an external signal can be fed to the key input of the gate, replacing the side-chain signal and controlling the opening and closing of the gate. I always derive such an external signal from a contact microphone gaffa-taped to the outside of the snare drum shell. My contact mic is an extremely cheap transducer (which can be bought from Maplin or Tandy) connected to a mic preamp via a piece of screened cable. A proprietary contact mic, such as a C-ducer, or even an accoustic guitar contact mic, will perform exactly the same function. Because the mic is in direct contact with the snare drum, it picks up the snare sound at a high level and does not suffer bleed from the other instruments.
In practice, gating drums to achieve separation is always a compromise. Although spill can be eliminated when the gate is closed, the spill will still be there when the gate is open and will affect the sound of other instruments, as each mic picks up all the instruments in the kit to a certain degree.
As with compression and gating, EQ may be applied either when recording or mixing. However, because the drums and percussion are only one element of the final track, and many of the decisions regarding EQ can only be taken in context, when the drums are heard alongside the other instruments, it's generally more advantageous to record a flat (unequalised) signal to tape, so that at mixdown you will not have to remedy any bad decisions taken at the recording stage.
There are times when it's desirable or even necessary to EQ at the recording stage: for example if you want to treat four different areas of the frequency spectrum and your mixer only has 2-band or 3-band equalisers, you could treat some areas while recording and the remainder in the mix.
The purpose of EQ is firstly to make the sound of each individual percussion instrument as good as possible, and secondly to make sure that all the instruments in the arangement sound good together. Whereas with most instruments and vocals I usually find subtractive EQ (cutting unwanted frequencies rather than boosting those that I want) preferable, with drums I regularly apply both boost and cut.
The frequency spectrum of percussive sounds can be divided into main areas of acoustic energy:
Below 1kHz, but principally in the range from 75Hz to 300Hz, lies the main resonance of the instrument.
From 1kHz to 3kHz is the 'bang' of the beat.
From 5kHz to 10kHz is the 'click' as the stick impacts with the drum or cymbal.
From 8kHz to 15kHz is the resonance of cymbals.
If the sound of any drum is blurred and the beats are indistinct because the drum's resonance does not decay between beats, an effective remedy can be to tune the equaliser to the resonant frequency, and cut. This technique is particularly applicable to fast songs.
Where drums have been recorded using a simple microphone setup -- just overheads, or overheads supplemented by mics on the bass and snare drums, for example -- there is nevertheless plenty of scope for creative equalisation.
Boosting in the region between 8kHz and 10kHz will make the cymbals more prominent and sparkling.
Boost applied in the 5-8kHz area will bring out the stick noise on both snare and hi-hat.
The 'bang' of the bass and snare drums and the toms can be adjusted by boosting or cutting at around 1kHz to 3kHz.
The body resonance of the drums can be augmented or reduced by EQ-ing from around 100Hz up to 300Hz.
Be careful in boosting frequencies below 500Hz, because a confused, muddied sound can result. To improve clarity, cut frequencies between 200Hz and 400Hz.
These frequencies are given as a guide only, and should be used as a basis for experimentation: it is essential to listen carefully and sweep the frequency control on the equaliser to get the best sound. (See also the 'Accentuating The Positive' box on the left for drum-specific EQ tips.)
Reverb is an important constituent of any modern drum sound, but it is equally important that the drums should not be swamped with a reverb which hangs on for too long and does not decay between drum beats, resulting in a muddy and indistinct sound. It's best to use a reverb with a short decay time (generally no more than 1.5 seconds), and to cut some of the low-frequency content from the reverb.
I normally assign the toms, snare and hi-hat a short, crisp plate program, with a reverb time of 1.2 seconds. A reverb with a longer decay time can be used on the overheads: cymbals, particularly, can be enhanced by a longer reverb. I often assign the overheads to my main reverb, using a hall programme with a decay of about 1.5 seconds. But these reverb times are a guide only, and you should set your effects to suit the particular track. Generally, fast songs require a shorter reverb time, to allow the reverb to decay between beats and thus avoid blurring the sound.
I rarely use reverb on the bass drum, because it tends to make the sound muddy and ponderous rather than punchy and dynamic. The exception is gated reverb, which can work well as a special effect, but should be used sparingly. This type of reverb continues to be popular, although the clichéd Phil Collins snare sound must surely have had its day. The easiest way to achieve this kind of sound is by using a dedicated preset on a multi-effects processor. Alternatively, the output of a digital reverb set to an ordinary reverb programme can be fed to a noise gate, and the attack, hold and release controls set to envelope-shape the output, to give the characteristic 'burst' of reverb abruptly cut off. If you are recording in a large, live space with a pleasant natural reverb, it's worth putting up mics at a distance from the kit to capture the ambience, and feeding the signal from these to a gate in order to envelope-shape it.
So there you have it! I hope you've enjoyed reading about the way a drum kit works and the factors which influence how it's miked and recorded. And if you're ever called upon to mic or record a kit, perhaps you'll approach it with less trepidation after having read this short series.