Following on from last month's article about drum miking, here we'll discuss the various ways you can mix and process your drum-kit mics.
Last month, we discussed the various types of microphone and mic positions you can use on a drum kit, and in this article we will look at the ways you can treat, manipulate and combine your mic signals. Once all your mics are set up and connected, it's time to start the soundcheck. It is common for soundchecks to begin with just the bass drum, followed by each drum in turn, but I have never found this a particularly useful or interesting way to soundcheck, preferring instead to get the drummer to play a simple beat or 'time' on the kick, snare and hi-hats. As I mentioned in my July 2012 article (/sos/jul12/articles/soundchecking.htm), this gives a better representation of the drum sound and is a lot less tedious for the drummer than playing single repetitive beats. Hearing multiple drums also gives you a chance to see how the various channels interact. Due to the inherent stupidity of microphones, they do not know whether they are snare or hi-hat microphones, and will quite happily listen to all sounds around them in a relatively undiscerning way. It is therefore quite important to get an idea of what your drum channels are doing overall.
Jam Out The Kicks
I will usually 
Many noise gates have a 'key filter' or 'side-chain filter' feature, which can be useful in preventing unwanted spill triggering the gate.start by pushing up the bass-drum fader (having first set the gain, of course) and listening to the channel at a reasonable level, but with flat EQ. Bass drums can usually do with a dip in the low mids to help clean up the sound, and the typical setup of a large-diaphragm dynamic mic just outside the drum will tend to benefit from some scooping of the lower mids around the 200 to 400 Hz area. Depending on the sound you're after, a small amount of high mid, in the 2 to 5 kHz area, can be added to give a bit of click. Rarely do I add bass to an external microphone.
If I have a boundary mic inside the drum, I will again take out any over-present low mids. I may also look at the high mids, often mellowing any harshness, unless I want a particularly aggressive sound. It is possible with internal mics to add in low end without too much fear that it will run away with itself. Where you add low end can be very dependant on the shortcomings of the speaker system you use, however. I tend to push the level of the low end and sweep until I hear where the low end works best , then back it off a bit. At this point it can be helpful if you have a variable high-pass filter and use this to filter out any sub that is present but not actually contributing to the sound of the drum. If it is a fixed-frequency HPF it may well be too high, but worth trying all the same. A low-shelving filter will gradually boost all frequencies below its turnover point, which isn't always helpful as this can lead to unwanted frequencies being boosted that are not contributing to the sound. Often very low sub frequencies can hinder the sound as they are using up amplifier and speaker power without adding anything positive.
Gaters Gonna Gate
When I am happy with the basic sound, I set up any inserts I have on the channel. These can be external devices, such as hardware noise gates or compressors, or plug-ins or internal processors if using a digital desk. For anyone unfamiliar with noise gates, they are a great tool for cleaning up sound: they 'open' (unmute) a channel when that channel's level reaches a certain threshold, and then 'close' when it drops below the threshold. They can be used to cut out background noise and, also, using the 'release' control, to tailor the decay of a note.
If the gate has a 'key filter' (sometimes known as a 'side-chain filter'), my first move will always be to set that. Key filters filter out what frequency area the noise gate is listening to when deciding whether it will open or close, but without affecting the sound of the signal going through the desk. I will usually set this to somewhere around the frequency of the beater hitting the drum, rolling off the low end so that the gate is effectively ignoring any stray bass or sympathetic resonances, and just listening to the beater strike the head. Most noise gates that have this feature also have a 'key listen' function, which enables you to listen to the same signal that the noise gate is using to trigger the opening of the gate. This will usually end up being a nasty, 'clacky' version of the drum sound, so make sure you turn the key listen feature off before continuing!
Having set the gate to listen just to the attacking part of the sound I will set the threshold so that it is opening just on the hits, making sure it's not missing any, but also not constantly opening on snare hits as well. I will usually set a short attack so the gate opens quickly, and set the hold and decay so the gate doesn't cut off any of the
Dbx 160As (the three black racks in the middle) are popular for live-sound compression work, not least because of their clear LED metering.weight of the drum and sound short. If the gate has a range control I prefer to set this so the gate doesn't close completely, but rather just attenuates the channel when the gate is not open, by between 20 and 30 dB — enough to help clean up the sound, but not enough to radically alter the overall sound of the kit every time the channel opens. If you have two microphones on the bass drum I will often link the gates so that the internal microphone triggers the gate for both channels, as it will get a better signal to key from and be less susceptible to low-end feedback and similar nasties. Linking gates makes one of the gates the master, and that controls the action of the second gate. This is a technique that I also use on snare drum (if I'm multi-miking), linking the top and bottom mics so that they both open and close at the same time.
Phase Time
If you are using two microphones in the bass drum you can run into the first of our major problems when miking up the kit — that of phase. Although the microphones are both listening to the same drum, they are doing so from slightly different positions. If they are placed at different distances from the drum, the sound from the two mics will have differing arrival times. This may only be slight, but when the two signals are combined they can suffer from phase differences. The most radical problem can be that they are 180-degrees out of phase. This will be clearly heard by listening to one channel, then adding the second: if the sound becomes thin and lacking in bass (or, in extreme circumstances, almost disappears) then the two channels are out of phase. When they are combined the waveforms will cancel each other out and only any minor tonal differences will be heard. This is most prevalent in the low frequencies and can result in a thin, tinny sound. By using the polarity reverse button on the channel, or by using a reverse-polarity cable (as I mentioned in last month's article), one channel can be have its signal inverted. When combined, the signals will hopefully now sum and produce a much fuller sound!
Another tool that many engineers (myself included) use to get around this problem is a 'phase alignment' tool. There are several hardware and software varieties available, and all are capable of continuously adjusting the phase of one of the signals so that it can sum with a second signal in the most musical way. With a kick drum this can often mean finding the point in the low end where both microphones sum most efficiently, producing a more satisfying thump. For more info on the subject of phase, check out our April 2008 article: /sos/apr08/articles/phasedemystified.htm.
When using two microphones I will often favour one, or the other, to produce different sounds. It is quite helpful to be able to adjust the sound of the drum by using more level from, say, a dynamic mic to produce a softer, rounded sound for acoustic numbers, and an internal boundary mic for harder rock or dance beats. This is a lot easier than trying to adjust the EQ on the channel between songs.
Compression
Compression on the bass drum can be applied in two ways. Either on the kick-drum channel itself (or channels, if you're multi-miking), or on an audio sub-group of the multiple mic channels. I will deal with kit sub-groups later, but compressing the kick drum on its own can help to tighten the sound considerably.
Drummers can hit the kick drum with a surprising dynamic range, from soft pushes to hard stomping beats. Compressing the signal can help even out these hits, and also help to protect the speaker system from the occasional over-enthusiastic beat. When compressing, though, it is always worth doing so after any gating, as reducing the dynamic range will make accurately triggering the gate less effective.
The type of compressor used is down to personal choice, but VCA-based compressors have always been a popular choice live, with the Dbx 160A being especially common. This is partly due to its simple controls and clear LED display, which is visible in any darkened room, but also to the way it can add weight and tighten up the sound. When you have more than one microphone on a drum it is worth grouping the channels together and compressing as a whole as this will help produce a more cohesive sound.
With the snare drum, gating is much harder as the level of spill from the top of the kit is much greater, making it very difficult to trigger gates accurately. However, gating any bottom snare mics can really help if the player is mainly playing steady hits. By gating the snares you can cut out any snare rattles and buzzes that can be caused by the snare resonating sympathetically with other instruments on stage, such as the bass guitar. I will rarely gate a snare-top microphone, however, as the sound of it opening and closing can usually be heard as it affects the sound of the hi-hats in particular. I will sometimes use the snare top mic to key the gate on the bottom mic, however.
Snare Treatment
Compressing snares can also help tighten the sound as well as even out erratic playing. Once again, grouping multiple mics and compressing the group can help. I will rarely do much EQ on a snare top microphone, other than using the high-pass or low-shelving filter to roll off any unwanted bass. Boosting the high mids can sound great when you are listening to just the snare drum, but when the hi-hat is played alongside it it can make the hi-hat sound trashy and over-present. This is one of the advantages of listening to the drums as a whole, rather than individually, as it means you will be able to hear how spill affects other channels, and how the bass drum may be triggering the snare gate unnecessarily.
The snare bottom microphone is normally more isolated from spill and I will often boost the upper mids if I need more 'crack'. I quite often see the bottom snare with all the low end rolled off, although I prefer not to do this as this channel can really help add weight to the sound without the need to over-EQ. Once again, it is a matter for experimentation and careful listening.
When I am happy with the kick and snare sound I will listen to the hi-hat, if there is one. Usually this channel is not adding much in the way of level, but rather crispness and attack, as the majority of hi-hat sound often comes from the snare mic. I will usually roll off the low end until it begins to sound a bit thin, then put some back in. This way I know I am not taking out more than I need.
With the kick, snare and hi-hat all in place I will check the levels. Faders work best when they are being operated around the 0dB mark. I prefer to start with them all at this point, so I will often make small changes to the channel gain so that with the faders in this position the drums are at the right level in the system and in the room. If you work with the faders near the bottom of their travel it is difficult to nudge them up without significant changes in gain. Too near the top, however, and you run out of places to go should you need a bit more, so the 0dB mark is a good starting point for all channels.
Back In The Room
At this point I always like to get out from behind the mixing desk and have a listen in other parts of the room. Quite often, mix positions can be deceiving: the thunderous sound produced under the balcony in the back right-hand corner can be just a limp rattle in the centre of the room, so it is important to walk around the venue to get an idea of the balance elsewhere. If there is a lot of bass missing then you just have to make a mental note of it, and try and mix a sub-heavy gig, taking as many opportunities during the show to get out and check as you can. Often a room that sounds bad during soundcheck will clear up when the audience arrive. At this point that it's worth checking how much headroom you have on the speaker system; are the amplifiers clipping at all? This will give you an idea of how much level you have to play with during the show.
At this point I will also have a listen to the overheads and get a rough balance with them. All the time I'll also be using any phase buttons to check relative phase between channels — does it sound better in or out? I will do this between any newly added channels. Often the kick will sound better if phase-reversed in relation to the overheads and snare top microphone. This is understandable, it is looking at the bottom of the kit whilst the others are looking from above. However, it is worth constantly checking!
Once I'm happy with kick, snare and hi-hat I will quickly check the ride as well, as part of a beat. This should keep up with the hi-hat in level and not fall away, as can sometimes happen. It is only after I am happy with this that I will listen to the toms individually. I will usually roll off the low end on toms to try and keep the sound as clear and as focused as possible. Once again, 
Setting your channel gains so that the faders are around the 0dB mark will leave you with the best fader resolution, as well as the option to turn up slightly if you need a little more level during the show.I usually roll up any high-pass filter until it is heard, then turn it back down again so it is not affecting the sound but also not letting through unnecessary lows. Gates can help on toms and be used to help taper the decay of the drum. By setting the hold (the amount of time the gate stays open) and decay (the amount of time it takes to close) times carefully, you can adjust any overly long ringing. However, with all these things it is better to have a look at the source before you try and fix the sound at the mixing desk. Most drummers like their toms to ring, and usually for longer than the engineer would like! However, it is always best to try and achieve a happy medium: talk to the drummer and explain that you don't want to kill their sound, merely control it so that the beat can come through more clearly.
Panning of toms is best not done to the extreme. Tom fills rolling from one speaker stack to the other can sound great in the centre of a room, but to half the audience they just fade away, or only appear half-way through a fill! I prefer to go for a nine o'clock, 11 o'clock and two o'clock approach, or variations on the above, depending on where I want the floor tom to sit in the mix.
Having gated the toms and checked them, I like the drummer to slowly hit around them with single beats so I can make sure they are at the same relative levels, and that one drum is not leaping out in level more than the rest. I will then get the drummer to smash around the cymbals to make sure that they are not causing the gates to leap open. Get the drummer to play some time with all the channels on, gradually getting him or her to add some tom fills to set the relative balance. At this point, double-checking all the compressors and gates to see that they are either not limiting too much, or in the case of gates, that they are opening and closing as expected.
Group Therapy
Whether you group the drums on a mixing desk, and how you do it, can be dictated by whether you want to then treat them together. Compressing the drums with a stereo compressor is very popular, but usually not as successful live as it is in the studio. Live, it can be a more hit-and-miss affair, and is often only useful to help contain them dynamically. Often, leaving out the overheads on any sub-group can help as you will get a more natural sound as they will not be affected by the compressors placed over the group. In the live environment heavy compression with low thresholds and high ratios will only end up bringing up the spill on stage from the other instruments, such as guitars and basses. The overheads are obviously most prone to this.
When mixing drums I will often group them as 'Beat' (kick, snare and hi-hat), and 'Kit' (toms and overheads). This gives a me a single fader to help push up the rhythm on some songs and back it down on others. I will often sacrifice stereo to achieve this control, if necessary, as the main beats are usually mainly mono anyway, the kick and the snare being panned centrally.
When I'm happy I will usually add some reverb to the toms and snare, depending on the sound I'm looking for. I have some generic go-to sounds that I tend to use on most shows. I have always found that darker plate reverbs suit toms well, as they tend not to over-accentuate any spill from the cymbals. On the snare I prefer a brighter plate or hall reverb, the choice depending on the sound I am hoping to achieve. I will often set up two reverbs on the drums and blend the two sounds. If I have the luxury I will send sound to several reverbs and use the returns to choose between shorter or longer times, EQ'ing the
drum reverb to tailor the sound to suit the drum as well as the room. It is always important to pay attention to the room acoustics. It will deaden when an audience comes in, but any long low-end ring will only reduce slightly, as it will be less affected by the audience absorption.
Working With The System
An important aspect of a good live sound is working with the sound system rather than against it. If you don't have much bass then pushing low end on drums will just overstress what you have. It's much better to reach a compromise and try to get a balance between the sound you would like, and that which the system is capable of. Note as well that if you are already peaking or limiting the system during the soundcheck, then during the show you will be really struggling when the musicians are full of adrenaline, playing harder and louder, and you are trying to get the sound over the noise of the audience as well. I find it helps to try and leave something in reserve.
Once I'm happy with the overall drum sound, I like to quickly soundcheck the bass, then get the two to play together. This gives me a good idea of how the rhythm section sounds, and also gives the drummer and bass player a chance to check that they can hear each other OK. If all is good, I'll send them off to get a quick cup of tea and move on to the rest of the band!