Loop Junkies’ Paradise

In Pro Tools 7.4, Digidesign introduced a new time-processing engine called Elastic Audio, which combines high-quality transient detection algorithms, beat and tempo map analysis, and realtime time compression and expansion. It’s difficult to sum up Elastic Audio neatly, because it isn’t a single tool or feature. Rather, it offers a fresh and powerful approach to manipulating the tempo of audio in real time as easily as if you were working with MIDI data. In other words, it’s a Big Deal.

With Elastic Audio, Pro Tools analyzes audio files for transient “events,” which could be a drum hit, a strummed guitar chord, or the start of a vocal phrase. These detected events serve as markers or control points for “warping” the audio. As you’d expect, Pro Tools can automatically warp audio regions to conform them to your session tempo, but there’s more to it than simply syncing beats. You can adjust warp markers manually, letting you fine-tune the timing of a performance. Even cooler, you can quantize warp markers, making it possible to conform audio loops with different feels to a common groove. For musicians who work with loops, this is a huge advantage that they no longer have to venture outside of the Pro Tools world to enjoy.

I’ll be the first to admit that Elastic Audio isn’t something new under the sun. If you’ve worked with REX files and ReCycle, or programs such as Ableton Live and Sony Acid, Elastic Audio will feel very familiar. However, Elastic Audio sounds better than a lot of other methods of time-stretching, and it’s tightly integrated into Pro Tools, making it an effective way to work with loops and phrases without having to use third-party utilities or DAWs. It’s as if all the best practices of time-stretching have been seamlessly combined within one program. Sound interesting? Of course it does. To help get you up to speed, check out the following tutorials on all things Elastic. Enjoy!

Elastic 101

In Pro Tools 7.4, you’ll notice a new set of Track controls for Elastic Audio (Elastic from here on). This is because Elastic works at the track level, and must be enabled on a per-track basis before you can use any of its time features in your session. The controls are located below the Voice and Automation Mode selectors. Hold-click the menu button to choose one of the four Elastic plug-ins; Polyphonic, Rhythmic, Monophonic, or Varispeed. These are algorithm choices: Polyphonic is suited for strings, pads, and even complete stereo mixes, Rhythmic is best for percussion loops, and Monophonic for melodic phrases. Varispeed, unlike the others, works like tape — changing tempo will also affect pitch.

Now Pro Tools will automatically analyze audio regions that get placed onto this track, according to the selected Elastic plug-in. Likewise, any audio recorded onto an Elastic-enabled track will become elasticized. As you’re arranging your audio regions, keep in mind that you can’t mix Elastic plug-ins on the same track.

Elastic-enabled tracks can be either sample- or tick-based (indicated by the small green metronome icon located next to the Voice selector). Both let you apply realtime Elastic processing by editing in Warp view (more on this later), and let you use PT’s audio quantization features. However, only tick-based Elastic tracks automatically follow tempo changes in your session. So for Ableton Live-like behavior, where tracks automatically follow your project’s tempo, use tick-based Elastic tracks. To have all new tracks be tick-based, enable the “New Tracks Default to Tick Timebase” option in the Editing Preferences page.

Elasticized Browsing

PT can use Elastic to automatically beat-match loops to current tempo when auditioning files from the Digibase browser. This makes it much easier to find loops that will work together in your project. Additionally, loops will automatically sync up when you drag-and-drop them into an audio track.

Open the Workspace Browser (Window menu), and choose a loop. Here I’ve drilled into a folder of 127 bpm loops. At the top of the window, the four Elastic algorithms are available.

By default, Polyphonic is selected. However, Pro Tools hasn’t yet determined these loops’ tempo. I first have to turn on Elastic in the Browser by clicking the “Audio Files Conform to Session Tempo” button — it’s the metronome-looking button along the top, next to the audio meters. Once this is enabled, files auditioned from the Digibase browser will be analyzed and played back at the current tempo. Once a loop has been analyzed, a checkmark appears to the left of the loop’s name and the loop’s duration will be updated. Analyzing audio files one by one when auditioning in the browser can get tedious. To make the process faster, you can batch-analyze loops by selecting multiple files or even entire folders, then choosing “Calculate Elastic Analysis” from the Browser menu.

Elastic Properties

There may be times when you’re working with audio regions that haven’t been properly tagged with the correct tempo or duration. For example, let’s say you’re working with an audio loop CD that has multiple loops per track. When you load one of these tracks in as an audio region, you’ll need to divide the track into individual loops, and then set each loop’s Elastic properties before Pro Tools can sync the loops to the session tempo.

To illustrate, here I’ve trimmed out a two-bar drum loop from a much longer CD track that contained four other loops. I’ve selected Rhythmic as my Elastic plug-in mode, but Pro Tools hasn’t yet determined the tempo of this loop. To set the tempo, select the loop then choose Elastic Properties from the Region menu. (Alternatively, type Option- or Alt-5.) The Elastic Audio Properties window will appear. Here’s where I can set the region’s original tempo, length, and meter. Since I’m working with a two-bar loop in 4/4, I’ve entered two bars as the Source Length. With this information, Pro Tools has calculated the original tempo to be 79.8 bpm. Now the loop will play back correctly at the current session tempo.

Warp & Event Markers

In order for Pro Tools to do its time-stretching magic, it uses markers to identify transient and tempo data. Specifically, there are three types of markers: Event, Warp, and Tempo Even-Generated Warp markers. These are visible in the new Warp view.

Event markers identify transients detected when Pro Tools performs its Elastic analysis. These markers are created whenever an audio region is analyzed. In Warp view, Event markers appear as grey vertical lines that extend almost to the top of the region.

You can drag these markers to time-compress or -expand entire regions or just specific segments of a region, allowing you to time-correct performances. This process, which Digi calls “warping,” has tremendous possibilities. For example, you could syncopate a four-on-the-floor loop, massage a vocal to make it more interesting, or precisely match the hits of one loop to another.

You can manually warp audio in one of three ways: Telescoping warp, Accordion warp, and Range warp. There isn’t space to go in-depth on each of these methods. However, to get you started, let’s look at how Telescoping can be used to quickly beat match a 12-bar stereo mix audio file to the session tempo and Bar/Beat grid. (You could use this technique to beat-match an entire song.) Here, I’ve dragged in the stereo file, which was originally at 90 bpm. My session is at 93 bpm, however. By zooming in on the region, you can see that the Event markers don’t line up with the Bar/Beat Grid.

At this point, you could try dragging the end of the region to the closest barline. To do so, use the Grabber tool, and position the cursor over the edge of the region. The Grabber will change to the Telescoping Warp tool.

Depending on the duration and complexity of the audio material, and the accuracy of PT’s Elastic analysis, you might get good results. However, you’ll probably need to fine-tune the warping measure by measure. To do this, zoom in on the Event markers so you can see the downbeats of the audio in relation to the grid, as shown here.

Grid line vs. Event marker

Drag the first downbeat Event marker so it lines up with the grid, then Control-click the marker to lock it in place. It’s now a Warp marker, as indicated by the solid line with a triangle base. Continue adjusting the downbeats until the entire audio track is locked to the grid. This technique is invaluable for remixing and mashing up songs. Now let’s look at how Elastic can be used to quantize audio.

Quantization

All of the options you have available for quantizing MIDI regions are also available for audio. This means you can quantize loose performances to a metronomic grid and even conform multiple loops with varying feels to a common groove template. Let’s look at quantizing audio to one of the included Groove Templates that comes with Pro Tools.

Start by dragging a loop onto a tick-based, Real-Time Elastic audio track.

Next, select the region, then choose Quantize from the Event menu’s Event Operations.

From the Quantize dialog box that appears you can choose from a variety of options. Here, I’m going to choose a groove template from the MPC Style folder. To quantize the audio, you’d select a template and click Apply. It’s that simple. Alternatively, you could create a groove template from your loop using Beat Detective. This template could then be used to conform other loops to a common feel.

For more tips on using and abusing Elastic Time in Pro Tools 7.4, be sure to check out the video tutorials on Digi’s website featuring industry veteran Phil Jackson. In particular, Phil’s tricks for creatively warping audio are well worth exploring.