Drum Replacement Primer

Nov 1, 2006 12:00 PM, By Alec Tabak

           

Give Yourself a Hand

Drummers hit the snare drum in several different ways. Each hit has a unique sound, which your replacements should mirror. If the drummer plays a rim shot, for example, your replacement sound should be a rim shot as well (see Fig. 1). A snare's timbre may become brighter as it's hit harder, but not as much as a kick drum's.

There are several ways to add replacement drums to your songs. The part you're replacing will often dictate the best approach. You can replace simple kick and snare parts in any digital audio sequencer using nothing more than its built-in editing tools. For instance, a rock song with a basic backbeat, even dynamics, and few fills or fast-repeating hits on the kick and snare is a strong candidate for replacement by hand. If you want to replace a drum sound in just one section of a song, you can also do that manually.

Create a new audio track for your replacement samples beneath the original drum track. If your sequencer doesn't automatically compensate for plug-in — induced latency, turn off any plug-ins that may cause playback timing problems on the original track.

Your goal is to align one replacement sample with each transient on the original track. Transients should be easy to spot in the original audio waveform, although an original track with excessive leakage can make this a little tricky. Audition the original track while looking at its waveform and get a sense for what the hits you're replacing look like.

In Digidesign Pro Tools, you can use the Tab to Transient feature. Steinberg Nuendo offers hit-point detection functions for locating transients. With sequencers that lack a comparable feature, use the Strip Silence feature on a copy of the original track to separate the transients from surrounding leakage. This method works in most sequencers, such as Steinberg Cubase, MOTU Digital Performer, Apple Logic (but be sure to strip silence within the Arrange window), and Cakewalk Sonar.

Loop the first bar of the song where the drum you want to replace is hit. Next, paste a replacement sample at the first transient, solo the original and replacement tracks, and click on Play. Panning the original and replacement tracks apart will make it easier to hear whether the hits sync up. With your program's window resolution high, nudge the replacement until you hear it double the original hit. Note that the original and replacement hits may sound best a few milliseconds apart. If that's the case, maintain this offset when positioning the rest of your replacement samples.

Listen carefully for phase artifacts between the original and replacement samples. To correct phase problems, begin by inverting the phase of your replacements. If that doesn't help, insert a sample delay on the replacement track and adjust it one sample at a time until both tracks are in phase.

If you're replacing a drum part in which the drummer plays a roll or a quick succession of beats, you'll need to build small crossfades between your replacements. If you let the replacement samples cut each other off, the effect will often sound unnatural and drum machine — like. Building dozens of crossfades may be tedious, but the extra effort will pay off in the final mix.

MIDI Me

Back when automatic drum replacement was a luxury available only in elite studios, MIDI provided a relatively economical way to replace drums without rerecording them. Today, MIDI drum replacement remains a viable option for fixing your drums before mixing, even if you didn't have the foresight to put piezo triggers on the kit you tracked.

Writing MIDI data from audio drum tracks works the same way as recording MIDI simultaneously with audio. All you need is a trigger-to-MIDI converter such as the Roland TMC-6 or a drum brain that accepts trigger inputs. Send the audio drum track you want to replace out of your DAW and into the trigger-to-MIDI converter. The device will have sensitivity settings — chiefly, a triggering threshold and several Velocity curves — but your trigger-to-MIDI converter will need extra help in order to respond accurately to your audio tracks.

To improve tracking, gate the original drum track, setting the gate's threshold just below the quietest transient and use as short an attack time as possible; you'll arrive at properly short sustain and release times after a bit of experimenting to find your trigger-to-MIDI converter's sweet spot, where each hit on the audio track yields a single MIDI note. Once you've created a complete MIDI track, you can use it to drive the drum sample playback software or hardware device of your choice, having saved yourself hundreds of mouse-clicks.

Automatic for the People

For complex kick and snare parts, manual drum replacement may be too time-consuming or impracticable. An automatic drum replacer plug-in can speed up your work tremendously because it listens to an audio track for transients and uses this data to trigger replacement samples.

FIG. 2: Drumagog’s main screen offers a variety of controls to let you fine tune the plug-in’s response to your audio track.

To optimize the plug-in's performance, you will want to prepare special duplicate versions of your original tracks that emphasize the transients (see the sidebar “Planning for Replacement”). For example, you can use sharp EQ cuts to get rid of as much drum tone as possible. A gate with a fast attack and short hold and decay times may be inserted after the EQ as well. It doesn't matter how these tracks sound at this point, because you'll be replacing their contents completely.

In the following example, I will use Wavemachine Labs Drumagog for automatic drum replacement (see Fig. 2). It is available as an AU, RTAS, and VST plug-in, and it supports WAV, AIFF, SDII, and GIG audio formats, as well as samples in its own GOG format. However, the basic principles are the same with other automatic replacer plug-ins, such as Digidesign TL Drum Rehab, Digidesign Sound Replacer, and apulSoft aptrigga2.

Speedy Snare Surgery

In almost every style of music, the snare drum is the most challenging drum to replace. No other drum in the kit is capable of producing a greater number of distinct sounds depending on where, how hard, and how frequently it is hit. A snare replacement track may easily require a dozen discrete samples to sound realistic if the drummer's part is even moderately complex. An auto replacer plug-in is perfect for such a big job.

To get started, insert Drumagog on your replacement track, select a multisampled snare drum from the sample bank, set the blend knob to 50 percent to hear an equal amount of the original and replacement audio, and click on Play. If things sound a little off, adjust the Sensitivity control (or the threshold parameter in other plug-ins). Every hit that exceeds this threshold triggers a replacement sample.

If drums other than the snare are louder on the snare track than the quietest snare hit, you probably haven't done enough prereplacement preparation. However, you may still be in luck if the nonsnare hits are not too close to the snare hits: by adjusting the Resolution (or attack) control, you can delay replacement retriggering. A 100 ms attack time is a good starting point.

Drumagog also has a pair of neat features for dealing specifically with bleed. Let's say you didn't mic the drummer's hi-hats separately, and you like the sound of the hi-hats bleeding into the snare mic, but not the snare sound itself. Select Stealth mode and listen as Drumagog passes the original hi-hats through, crossfades in with a replacement snare, and crossfades back to the hi-hats.

What if you hear too much of the old snare sound in your overheads? Put Drumagog on the overhead tracks and set it to autoduck when the snare hits. This lets you use the plug-in like you would a sidechain on a compressor.