What's Up, Stretch?
Mar 1, 2008 12:00 PM, By Jason Scott Alexander
Flex and flow with audio tracks using Elastic Time in Pro Tools 7.4
After a long wait, elastic audio technology has finally come to Digidesign Pro Tools 7.4 (including Pro Tools 7.4 LE and 7.4 M-Powered). Using a set of powerful new time compression and expansion (TCE) algorithms, Elastic Time lets you manipulate audio in real time as if it were MIDI data, quickly moving notes, warping phrases and easily beat-matching audio to a session — all with absolutely no tempo constraints.
POST-WRAP 'EM: Here are audio tracks before and after quantizing, which adds Warp markers. The Elastic Time Rhythmic plug-in window is fine-tuning the Decay parameter of one of the percussion loops to get it in the pocket with the main groove.
Not to be confused with the distinct skills of Beat Detective, which manipulates discrete, slice-based locations of recorded audio, Elastic Time fluidly stretches waveforms without cutting the audio. It's ideal for situations where audio should be malleable during experimentations with phrasing and groove construction, or when you don't know what your final tempo will be while laying rhythm parts. Elastic Time also preserves the built-in feel of audio as you apply groove templates or quantize, allowing for much bigger changes in tempo than Beat Detective can do — with little to no sonic degradation, even at pretty extreme tempo changes.
HOW IT WORKS
In Pro Tools 7.4, you can assign audio tracks to one of four Elastic Time algorithms that operate either in real time or as rendered processes. The algorithms are essentially plug-ins — Polyphonic, Rhythmic, Monophonic or Varispeed — instantiated in the track controls area of the Edit window. Each is designed with specific styles of TCE playback in mind.
For an audio file to be considered “elastic,” it must be analyzed by dragging a file onto an Elastic track or changing a current audio track to play with an Elastic algorithm. In either case, the file goes offline momentarily for the software to detect its transient events; you can see the results by switching to the new Analysis track view, where Event markers show up at each detected attack transient.
I like to call up the DigiBase browser to import and analyze audio, mainly for its ability to audition files against a session already in playback mode. With the new Conform to Tempo button switched on at the top of the DigiBase window, files are automatically analyzed and locked to the session's tempo, even before the next downbeat comes around. That lets you hear which of the four algorithms works best before actually importing files into the events list. You can save time by right-clicking on any drive volume or folder within DigiBase and having Pro Tools analyze the files in the background, without stopping the flow of the session.
POLYRHYTHMIC MASSAGE
With analysis markers in place, the speed of an audio file changes relative to any tempo change — even though the audio file itself has not yet conformed to the actual bars and beats of the Pro Tools session. Quantizing an elastic audio region (using the standard Quantize window) automatically creates Warp markers from underlying analysis markers. If you switch your track view to the new Warp View mode, triangles at the base of each attack transient indicate the transformation.
Think of Warp markers as little handles that anchor specific points in the audio file (typically detected transient events) to the timeline to correct or adjust the timing of a performance. There are three types of warp behavior: Accordion Warp expands or compresses audio on both sides of a single Warp marker equally — useful when the downbeat occurs in the middle of the region; Range Warp performs TCE between two fixed points only; and with Telescoping Warp, the entire audio region stretches proportionally to match the session tempo map and Bar|Beat grid. In Warp view, you can add, relocate and delete markers to suit the task.
When you slow down or speed up a session's tempo drastically, reach for the Elastic Time plug-in window. Depending on the algorithm in use, the window will usually contain only a single context-sensitive parameter. The general-purpose Polyphonic algorithm has a parameter that allows you to tighten or loosen the response of the TCE envelope around instruments such as guitar, complex loops or multi-instrument mixes. Best suited for drum tracks and percussion loops, the Rhythmic plug-in features a Decay Time parameter for trimming the tail end of elastic expansion. When applied on a track-by-track basis, it lets you fine-tune the way multiple percussive tracks fit in the pocket together — great for tightening up the sha-woosh at the end of a stretched-out snare that's been slowed way down, for example. You never have to worry about the Rhythmic algorithm smearing attack transients because it works by letting a short period of audio after each Warp marker go by unchanged before starting any time compression. Smart.
Another very cool feature lets you copy groove templates — as extracted by Beat Detective — to an audio file. That can be extremely useful in applying the feel of a live drummer to a rigid electronic loop or to a bass line that you recorded in another session. On material where you want to keep the formant relationships intact, such as bass or vocals, the Monophonic algorithm is the one to use. With no editable parameters, you simply set it and forget it.
RUBBER-BAND ORCHESTRA
Aside from its obvious corrective nature, Elastic Time is also an amazingly flexible remix tool. For example, performing stretch-effects on drum hits and vocals using the Polyphonic algorithm, you simply grab the tail-end Warp marker and drag the note out for as long as you wish. It's perfect for vocal stutters, and you don't waste time with offline processing.
Another common remixing trick repeats samples in rapid fire at build-ups and transitions. Previously in Pro Tools, you'd have to do that by trimming it down to a single hit and duplicating the region dozens of times. Now, head to the Elastic properties box, click on the “1/2” button next to the Source Length display, and you instantly turn a standard two-bar eighth-note snare fill into a one-bar 16th-note roll. Halving it again yields a tight 32nd-note roll. Duplicate the region a few times, and you're done.
You can also use Warp markers to manually regroove audio parts with completely fluid and natural results. Take a highly staccato 16th-note arpeggiator loop: By adding new Warp markers anywhere within the decay portion of a particular note and stretching it, you can introduce lofty hang times and change its phrasing entirely. Other great uses for the technique include refitting vocals, interpolating sample replays and introducing variation to an electronic kick drum loop by stretching only certain beats, so as to match or play off the spaces within a live kit pattern.
For a completely wacky effect, try linking pitch together with time compression using the Varispeed algorithm to produce a cool tape-life effect. I often set that loose on breakbeats, so as you move Warp markers back and forth, the pitch jams up and down for a trippy hop-skip-and-jump sound. Of course, the timing remains perfectly on tempo, catching up or falling back as necessary.
Digidesign recently posted the 7.4cs2 update, which changes the behavior of Elastic Time's quantization beneficially for multitrack drums. Previously, it quantized from the transient nearest to the grid, but Pro Tools now picks the earliest transient across grouped tracks for a given hit — that is, the first mic that records a hit. That's a huge improvement for multitrack audio.
| Want to use this article? Click here for options! |  |
