TL Labs TL Drum Rehab

Beefing up real drums with samples is routine practice these days, but the standard tool is looking pretty dated. Can TL Labs' new plug-in help us do it better?

One of the many innovative software tools that has helped to make Pro Tools an industry standard is Digidesign's Sound Replacer. An off-line plug-in that can scan an audio file for transient hits and drop in new samples to replace or augment them, Sound Replacer has probably been used on more mixing sessions than cocaine. However, while Digi's other great drum-fixing tool, Beat Detective, has been continuously improved over the years, Sound Replacer has never really been updated, and these days, it's looking increasingly long in the tooth.

Trillium Lane Labs obviously felt the same, and decided to create a third-party alternative. During the development process, TL Labs were acquired by Digidesign (now Avid), so TL Drum Rehab can be considered an 'official' alternative to Sound Replacer.

Visually, Drum Rehab is very much of a piece with TLL's TL Space convolution reverb. A file browser at the right-hand side is used to locate and load in samples, with the bulk of the window given over to a large waveform display which has several different functions. This is very clear, though like all RTAS plug-in windows, it can't be resized or navigated using keyboard shortcuts. Drum Rehab only works on mono tracks, and oddly, is classed as an Instrument in the Pro Tools plug-in list.

Instant Results

Until now, there have been two contrasting approaches to the design of drum-replacement plug-ins. On the one hand, you have the likes of Wavemachine Labs' Drumagog, which is inserted as a real-time plug-in across a mixer channel in your DAW. With this approach, you get instant results, but you're completely dependent on the plug-in's automatic detection algorithm to identify beats in the source audio; beyond fine-tuning the detection parameters, there's little you can do to correct false triggers, add missing beats, or tighten up timing. On the other hand, off-line tools such as Sound Replacer allowing you to edit triggers and their timing at your leisure, and display the results against a waveform view of the source audio, but are less clever when it comes to auditioning the results in context.

Nudging the position of a trigger in Expert mode. Note how TL Drum Rehab overlays the waveform of the replacement sample in green so that you can line up the two transients perfectly. TL Drum Rehab represents an attempt to combine the best aspects of both approaches. In essence, it's an RTAS-format plug-in that can detect and replace drum beats in real time. However, as Drum Rehab is 'listening' to the source audio, it also builds up a 'map' showing where all the detected drum beats fall. These trigger points are displayed against the source waveform in the plug-in window, and can be edited after the fact to fix any mistakes made by the automatic detection algorithm.

With an off-line plug-in like Sound Replacer, you can simply click a button to load an audio Region instantly into the waveform display. This isn't possible in an RTAS plug-in like Drum Rehab; instead, you have to hit Play and watch as its display is slowly filled in real time. I expected this to be a complete pain, but in actual fact, it really isn't a problem. As long as your source audio is reasonably consistent, you need only analyse a short section of it in order to set Drum Rehab parameters that will work for the whole song. What's more, Drum Rehab will 'remember' every section of audio you play it, even if you're hopping backwards and forwards along the timeline or editing another plug-in, so in effect, you can leave it to build up the complete waveform analysis in the background.

There are no horizontal zoom or scrolling controls within the plug-in window, but what's shown in the waveform display always reflects the selection in the Pro Tools Edit window. If it's zoomed out too far and you can't see what's going on, just make a shorter selection and it will be scaled to fill the window. In practice, this is completely painless, and far better than Sound Replacer 's tiresome zooming and scrolling.

The Easy Option

In effect, TL Drum Rehab offers two levels of operation. The trigger points that are detected in real time as you play through your audio Region are stored along with the waveform 'map' that gets built up in Drum Rehab. In the default Listen mode, these stored triggers are not used; the plug-in always analyses the input in real time, generating new triggers each time you play back your file. You can choose from four detection algorithms, optimised for kicks, snares and so on.

Where you have a fairly consistent audio source without too much spill, and you're happy with the original timing, this often works fine, and in this situation, the default Triggering window offers all the controls you're likely to need. Clicking on the arrows to the bottom left and right of the waveform display sets the minimum and maximum input levels that will trigger sample replacement. You can balance the levels of the input and replacement audio, with the further option to duck input audio when a trigger is detected, and choose whether dynamic variation in the original audio should be retained in Drum Rehab 's output. Once you've set the trigger levels, you can pretty much ignore the waveform display.

Call In The Experts

If your audio source suffers from excessive spill, wild dynamics or poor timing, you'll need to use Drum Rehab 's Expert mode. Here, the plug-in takes its cue from the stored 'map' rather than the input, the idea being that you can edit the map to fix problems that can't be addressed in real time.

The Commit function 'fixes' the automatically detected triggers for whatever part of your audio Region is selected, meaning that they won't be regenerated every time you play back the Region. Once Committed, triggers can be repositioned, Uncommitted or Ignored. The method by which triggers are moved is beautifully thought-out, and makes light of the interface limitations imposed by the plug-in format. Clicking and holding on a trigger zooms the display automatically to sample level, whereupon you can drag left or right to adjust the position. If you have a replacement sample loaded into Drum Rehab, you'll see its waveform overlaid in green, which makes it dead easy to line up transients precisely and check that the original and replacement samples are in phase. You can also Command or Ctrl-click and drag to alter the amplitude of a trigger.

On the down side, the zoomed display doesn't scroll, so it's only feasible to nudge triggers by a few tens or hundreds of samples — there's no easy way to move them larger distances. And although it is possible to add new triggers where Drum Rehab 's detection algorithm has missed beats, this can only be done while you don't have any part of an audio Region selected in the Edit window, which can be a nuisance.

It's also possible to quantise triggers within Drum Rehab to the Bars + Beats grid in Pro Tools. The only options here are the quantise resolution (from half to 64th notes) and a slider to tell it what degree of correction to apply. The process works fine, but is completely dependent on having an accurate tempo map within Pro Tools. There is, for instance, no way to tell Drum Rehab that a selection contains triplets; you have to make sure that Pro Tools is aware of this.

If you close your Session, TL Drum Rehab 'forgets' its waveform analysis and any Uncommitted triggers, but remembers the positions of the Committed triggers, so any edits or quantisation you've applied will be retained — and, as ever, you can rely on it to redraw the waveform in the background when you first play through the Session. It's another point where the potential difficulties caused by the choice of a real-time design have been neatly sidestepped.

However, there is one area where these difficulties are unavoidable. There will come a stage in many projects where you want to convert Drum Rehab 's real-time output into a recorded audio file on a new track. This is more or less essential if you've done some work in Expert Mode and later decide to edit your drum parts or song structure — otherwise, your carefully edited triggers will no longer be in the right places. It might also be desirable in order to unload the plug-in from a Session to free up resources; although TL Drum Rehab isn't a big CPU hog, it holds its samples in memory.

Unlike Sound Replacer, which can create a new track and a new Region at the click of a button, Drum Rehab can only generate its output in real time. If you want to turn that into an audio file, you'll have to buss its output to a new track and record it, or solo the drum track and do a bounce, both of which mean stopping work for several minutes. If you do the former, you're also instructed to reset Pro Tools ' hardware buffer size to 2048 samples to avoid glitching. In both cases, there's no easy way to make Drum Rehab generate a 'pure' output consisting only of replacement samples. The Input level slider allows you to attenuate the source audio by up to 40dB, which is enough to make it inaudible in most situations, but I would have liked the option to mute it entirely. Instead, to create a 'pure' output you have to Commit the triggers and then mute the source Regions in the Edit window. Another option I would like to see would be to export, or record, Drum Rehab 's triggers as MIDI notes to feed to other plug-ins, but this doesn't seem to be possible.

Rehab Or Replace?

Despite these minor quibbles, I'm pretty impressed with TL Drum Rehab. Implementing something as complex as drum replacement in a real-time plug-in will always be a challenge, especially when you consider that RTAS plug-ins don't support keyboard shortcuts, or allow you to resize their windows, and TLL have really thought about how to make the process as painless as possible. TL Drum Rehab is more flexible, more powerful and much less annoying than Sound Replacer, and I for one have no intention of going back!