How To Replace & Reinforce Recorded Drums

Drum replacement is now a routine production job in genres ranging from pop and indie to high‑tempo metal, and even live sound.

Altering the timbre of your drum kit is one of the most dramatic changes you can make during a mix. To this end, EQ and dynamics processing (gating, expansion, compression, transient-shaping) have been used for many years, but increasingly, engineers are also 'triggering' drum samples to replace or augment recorded drum parts. But why resort to such a radical approach? After all, in these pages we regularly preach the benefits of getting everything right at the recording stage.

Sometimes, of course, it's because you don't have control over the recording, and simply have to make the best of what you're given — a scenario that will be familiar to anyone who reads our regular Mix Rescue feature! Even when you're managing the session, though, you might not have the opportunity to capture everything quite as you'd like to. The performance might be great, but for the drummer having a rather limp kick-foot, for example, or it may contain inconsistent-sounding snare hits where the drummer's strokes are straying away from the centre of the drum. Or perhaps you're dealing with a live recording, where you're at the mercy of the performance on the night, the inevitable leakage, and the acoustic environment of the venue. In fact, drum replacement to augment such live recordings is commonplace — and you might be surprised by the names of some bands whose live DVDs feature drum replacement.

The use varies from genre to genre. Typically, in genres such as indie or soul, much of the feel of the performance is likely to come from nuances in the way the drums have been hit — so you can use drum replacement in those genres, but your result will usually need to be more natural and less obtrusive, and to take much more account of the dynamics of the performance, than in 'harder' styles.

It's not always about compensating for imperfections, though. Triggering is crucially important in rock and metal production, for instance, where the feel of a track will often rely on a sense of consistency between one strike and the next. Sixteenths played by a real drummer on the bass drum at 240bpm will inevitably suffer from a dulled attack, but with total sample replacement each bass drum strike can be as solid as the last.

Grammy‑winning producer Andy Sneap suggests that, in hard rock and heavy metal, sample replacement "is the only way to get the clarity required in the drums to cut through the wall of guitar that is expected these days.” If you're interested, Andy's use of both sample replacement and augmentation, and the wall of guitars that he has become renowned for, can be heard on Testament's 2008 album, The Formation Of Damnation.

If using replacement as a creative rather than a corrective technique, the results can be as obvious as you like. Sonic Boom 6's recent cover of 'Addicted To Bass' is a good example: although the whole song was tracked with a live drummer, 808 samples, hand claps and even different snares have been added, to keep the sound of the drums ever-changing and exciting throughout the track.

There are also some clever and subtle applications for drum replacement that can help you give your finished tracks in a range of genres that bit more professional polish. Mix engineer Andy Wallace (of Nirvana Nevermind fame) reportedly devised the trick of triggering a sample from the snare but sending that sample 100 percent wet to a reverb, rather than to the master or drum bus. The reverb return can be processed as much as you like — and the outcome is that you get the sound of the recorded snare, but with much more control over the ambience and reverb tail, which makes it much easier to fit into the mix.

The Starting Line

Drum triggers such as this DDrum device are commonly used during live performance these days, but they can also prove a useful ally in a studio recording session.

If you want to replace any drum parts, and have the chance to influence the recording session, the mantra of 'get it right at source' still applies. Drums are transient-rich sounds, and all of the replacement techniques discussed in this article rely on detection of the drum transients, whether that be for lining things up by eye, or to make the transient detection easy for automatic drum‑replacement plug-ins.

At the most basic level, then, you'll need a clean, close-miked, multitrack drum recording. If you have a close-miked kick recording, unless you've recorded very badly, it's pretty easy to spot each hit in your DAW; even snare leakage is likely to be much lower in level than the kick. But it's not always that easy: a tom recording, for instance, may include significant leakage from the snare or cymbals. This makes it trickier to detect each hit. It's usually possible to duplicate the part and EQ it to isolate the desired hits, and then feed that to your trigger software, but that can sometimes be more problematic than it sounds, and even where it's easy it can be time-consuming.

What we need, then, is a clear indication of when the tom (in this example) is hit — and this is where hardware drum 'triggers' can come in handy in the studio...

Trigger Happy

Drum replacement can seem a sensitive subject to discuss with a band, but you'd be surprised by how easy-going many drummers are about this. For a significant number of rock and metal drummers, for example, using hardware triggers and samples during a live performance is now very much the norm: kick‑drum replacement is fairly standard; and a snare trigger blended with the miked signal is becoming commonplace; some heavier bands even opt for 100 percent sample replacement of the kit shells, leaving only the cymbals miked up on stage.

The triggers themselves are mounted on the shells of the kit. They have a transducer making contact with the skin of the drum, so that a fairly soulless-sounding click is output whenever the drum is hit, and the remainder of the time the trigger's output will be pretty much silent. The resulting signal can therefore be recorded into your DAW and used to trigger samples or drive sound modules or virtual instruments.

Yamaha and DDrum have led the way in the hardware trigger market for some time, though there are alternatives from the likes of Roland. Much of what you're paying for with commercial triggers is the mounting hardware: they're robust, which means they'll last, and they mount on one of the drum's lugs, which is convenient and has minimal impact on the sound of the drum. (In fact, if you're particularly hard up, you can make do with a humble piezo contact mic wired up to an audio lead and some sticky foam pads — and we'll be telling you how to do this in next month's SOS.)

You only need the audio from these triggers, though feeding the signal to a well set-up electronic drum 'brain' can make things easier. The Alesis range remains very popular for trigger-system brains, as not only do they have their own samples built in, they also have the trigger inputs and the facility to fine‑tune the response of the triggers, as well as providing a MIDI output. If you have a V-drum or similar electronic drum kit, you can put their brains to work in exactly the same way.

Andy Sneap provides 'Testament' that drum replacement has become the norm in rock and metal.As well as solving our trigger-signal problem (ie. you now have your transient with no leakage), recording a trigger signal can open up some other useful possibilities. For example, if you're aiming for an open and real sound on your toms and don't want to hard-edit them, but do want to gate them, you can bus the trigger tracks to the key inputs on noise gates inserted on the tom channels. The gates will open and close in accordance with the triggers, rather than the tom track that may have snare leakage.

If you know in advance that you'll be replacing one of the drums, you can totally damp it while recording, and record only the trigger output. With a snare, this will remove most (if not all!) of the snare from other mics and overheads, while still capturing a reliable trigger signal for your sample. Not only does that make it easier to process those mic signals, but it means that your choice of sample and processing isn't inhibited by the presence of the original snare in your overheads and room mics — and the sample will probably mask what spill there is.

Recording Session Samples

If your aim is to reinforce the sound of the kit, even though you're using triggers the usual rules for drum recording still apply: you should still set up the kit, tune it and mic it with the diligence you'd apply to any other drum recording; you're still going for a clean recording, with as much separation as you can get between instruments on the close mics.

At the start of the session, it's worth taking the time to capture some isolated hits of the different drums in your kit, at a range of velocities. That way, when it comes to editing and mixing, you'll have access to consistent samples of the recorded kit, in the same space and the same mics (including overheads and room mics) as the main recordings, but without any leakage from other kit pieces. Do this at the start of the session rather than the end and your samples will be of a higher quality, because they'll have been taken when the skins were fresh and the kit was fully tuned.

These samples can be used for anything from replacing hits on an otherwise perfect take, where a few snare strikes went slightly left of centre, to replacing the floor tom on the fast section where the drummer moved from the ride to a fill, thus stopping the ride spilling onto the tom tracks. Of course, another benefit of this approach is that as you undertake more and more recording sessions, you'll begin to build up your own, unique drum sample library, which might just get you out of a hole on another project!

Choosing & Using Samples

Sonic Boom 6 have been known to use multiple drum‑kit sounds in the space of a single song.

You don't have to limit yourself to using samples from the session, of course: a well-chosen sample from your collection, or a commercial library can be used. Perhaps the kick you recorded just had insufficient depth or click, for example: you can pick one that has the desired quality, filter out anything that's not wanted, and blend the result in with your recording.

There are some superb drum libraries to choose from. The likes of Fxpansion's BFD, Toontrack's Superior Drummer, XLN Audio's Addictive Drums and Steven Slate Drums offer excellent recordings of the finest kits available, tuned to perfection, miked by professionals and tracked at hundreds of different velocity levels, using quality equipment. This sounds appealing, but just because a kit was recorded by Joe Barresi or Andy Johns, it doesn't mean it will sit well in your track! Also, a possible down side to commercial sample libraries is that everyone else has access to them, which means that it's possible for people to recognise 'that' kick sound in your work.

So even though all that leg-work has been done for you, you'll still need to spend time choosing and processing an appropriate sample. One useful tactic is to try blending a selection of different samples, as that can result in a less 'spottable' sound. Constructive use of EQ, compression and transient designing can also help to make the samples fit the rest of your mix, and you might also find that pitch-shifting helps, particularly with more musical kit parts such as toms.

Remember that you don't have to limit yourself to drum samples, either: depending on the track, anything percussive might give you the added dimension you're looking for; or if it's just depth and fullness you need, it may be that a triggered synth works well. (You do need to be a little careful with sub-bass synths on kicks, though, as they invariably eat into your mix headroom if mixed in too high.)

Software Tools & Techniques

Modern drum replacement gives you an incredible amount of control over what samples are triggered and when. For example, in the first of these two Drumagog 5 screen shots, five different velocity thresholds have been defined. In the second screen, multiple samples from the same kit piece have been assigned to the five velocity groups. This means that not only are you able to trigger different samples for each velocity, but the plug-in can trigger different individual samples for each hit within that velocity layer. This overcomes the problem known as 'machine-gunning' — where the same sample is triggered several times in quick succession — and thus helps you achieve a more natural result.

Once you've recorded your drums and trigger signals — or have received your drum multitracks and decided you need to resort to replacement — and chosen the sounds you want to use, it's time to start triggering...

The approach over which you have most control is to roll your sleeves up and paste samples in by hand. You simply put them on a new audio track, align them by eye, and blend them in using your DAW's channel faders. This is a painstaking process, especially if you need to use different versions of your sample for each strike to give the performance a more natural feel. The tab-to-transient feature available in some DAWs make the process easier: you literally use the Tab key to move to the next transient, and then paste your sample on the adjacent track.

But you're looking for a more convenient, automatic approach, right? So let's consider how best to use modern drum-triggering software (some of the best of which is described in the box earlier in this article). All the leading drum-trigger plug-ins allow you to load a selection of drum strikes at various different velocities, and to assign them to different velocity groups. The user has control of thresholds for the level or the transients (or both), to determine when each bank of samples comes into play after the software detects the transient. You also have the option of how much to blend the sample with the original, from subtle reinforcement to total replacement.

There are two basic approaches taken by drum replacement software. The first is a real-time trigger: the software detects audio as it is being played (either with 'lookahead' for more accuracy, or in a 'live' mode). The second is an off-line system, whereby the sound is recorded into the plug-in and then analysed, so that you can tweak thresholds and other detection parameters in minute detail. Of course, some of the best software, such as TL Drum Rehab, offers you the option of either approach. However, it's often possible to automate thresholds on real time plug-ins, which can make them almost as flexible.

Set Phase To Stun!

Even when using sophisticated commercial software to replace your drum sounds, it's critical that you check for timing and phase alignment. In the first screen, you can see considerable discrepancies in timing of different outputs from an earlier version of a leading drum replacement plug in. In the second you can see ultra‑precise timing from a competitor, but it would appear that the sample could do with polarity inverting.It's hugely important that the original drum and the sample are both aligned and in phase with each other: the transients of both must start at the same time, and the waveforms must travel in the same direction. Otherwise, phase‑cancellation will rob your drum of power, and change its sound. If replacing manually, you can zoom in, line things up by eye, and, if necessary, polarity‑invert the sample, but even the best commercial drum-replacement software doesn't always achieve either of these things perfectly. So however much you've paid for your software, it pays to bounce down the results of its work as audio, so you can check for yourself that everything is optimally aligned. If not, you can use the time-alignment tools of your DAW (hitpoint detection, beat slicing, groove templates and audio quantising) to further tweak the drums towards perfection.

Overcoming Problems

Some elements of a drum performance will always be more difficult to replace than others — but it's fair to say that if you spend enough time and make enough of an effort, you can pretty successfully replace most performances.

Two common problems are snare rolls or flams and replacing hi-hats, particularly when the drummer switches between open and closed hi-hats. For the former, if you have difficulty setting the right transient detection thresholds, you might find that you can achieve a more convincing result either by automating the trigger plug-in's input level or multing the drum source out to a separate audio track, chopping it and automating its level before feeding it into your plug-in. Unfortunately, there's really no substitute here for hard work and effort.

For hi-hats, triggers aren't going to be a viable option, but a well-positioned close mic should at least give you a clean signal. The problem is that the range of sounds you can create by striking a hi-hat is huge: you can trigger it with your foot or your stick, it can be fully open or tightly closed, or anywhere in between... and so on. In practice, it's probably easiest to trigger the same sort of hit consistently, bounce to audio and then go in and edit to replace closed hits with open ones (or vice-versa) manually. Alternatively, this is one area where you can abandon triggering altogether and simply program the part from scratch — after all, you don't lose any marks for how you get the result, as long as you get it!

The Perfect Cheat?

Although it's still seen by some as a means of cheating, drum replacement is here to stay — and there's absolutely nothing wrong with that! If a project comes to you to mix and you feel the original tracking wasn't up to standard, you can do something about it. Even if the tracking is good, the powerful tools now available mean that you have more options and facilities at your fingertips than ever before.