When enabled, the Elastic Time plug-in analyzes two dimensions of your audio in order to calculate the recorded performance’s tempo. It looks at the audio region’s duration in bars and beats, and it looks for transients that represent a regular periodic rhythm in the recording. In theory, if the rhythmic content of your recording is clear, with distinct transients, Elastic Time can figure out a performance’s tempo regardless of whether the audio region is trimmed to a perfect loop or not. This is really neat when it works, but it doesn’t perform miracles (nor should you expect it to, that’s not producing your own music).

Instead of relying blindly on Elastic Time to perform your beat matching (as in, crossing your fingers and hoping for the best), there are several simple steps that you can take ahead of time to prepare the audio and ensure perfect results every time. Performing this pre-processing, even though it’s a tedious task, helps to preserve the audio quality and the groove of the original performance after your tempo change.

The easiest way to demonstrate my pre-processing approach is to take you step by step through the process. This is the best way to understand not only the steps in the process but the logic behind my approach. (Try it a different way and you’ll find out just how quickly you can end up with a train wreck.) The DRM (Digital Rights Management) free stems being offered for your remixing pleasure by Radiohead, of their song “Nude”, on iTunes is perfect for this example. The stems are $0.99 each and you only really need two of the five available, the “Drum Stem” and the “Voice Stem”. But, it’s nice to have all of the stems in your session, even if you don’t use the “Bass Stem” and “Guitar Stem” they’re handy for finding the key of the original, and the “String FX Etc. Stem” contains several sounds that are perfect for a remix.
iTunes Nude

Remixing Radiohead

1. Create a new Pro Tools session and import all of the “Nude” stems. When prompted, select the import Destination as New Track with a Location of Session Start.
step 1

2. Arrange the tracks in the Edit window with the Drum Stem on top and the Voice Stem just below.
step 2

3. Mute all of the tracks except the Drum Stem. Use Tab to Transient to locate the very first downbeat in front of the vocals (approximately 1946229 samples in from the session’s start) and separate the regions.
step 3

4. Select the Edit Group, double click on the latter Drum Stem region and separate all of the regions.
step 4

5. Select the Shuffle Edit Mode and delete the first set of regions so that the downbeat of the second set of regions scoots to the beginning of the session.
step 5

6. Disable the Edit Group and using Tab to Transient find the downbeat every two bars in the Drum Stem and separate the regions. (The only region that I left as 4 bars is the drum break, having 2 bars before the break itself.) In some instances, you can make the separations every 4 bars, but with “Nude” there’s a lot of human tempo variation and every 2 bars will produce the most precise overall beat match.
step 6

7. Select the Edit Group and double click on each 2 bar Drum Stem section and separate the sections.
step 7

8. Select each 2 bar section and apply Identify Beat to generate a tempo map for each section. This will beat match and lock each 2 bar section to your session’s tempo grid. (You could use Beat Detective to generate a tempo map, but my method preserves the original performance’s groove every two bars, while simultaneously guaranteeing that the original’s downbeat is locked exactly to the grid every two bars. This way, your beat match never drifts.) At this stage, it’s also helpful to create a Click track in order to audition your tempo lock.
step 8

9. Change the Timebase selector for all of the tracks to Ticks. This will lock the regions to their relative bar and beat positions so that they stay in beat when you make your tempo change. Then, enable the Elastic Time plug-in for each track. Set the Drum Stem to Rhythmic, the Voice Stem to Monophonic, the String FX Etc. Stem to Polyphonic, the Bass Stem to Monophonic, and the Guitar Stem to Polyphonic. Give Pro Tools time to analyze the audio. (For now, leave the Elastic Time plug-in set to Real-Time Processing.)
step 9

10. In the Transport bar, disable the Conductor and enter a new tempo in the Current Tempo field, or experiment with the Manual Tempo Slider. Since the original tempo is about 42 BPM, it’s nice to bring the tempo up to about 62 BPM. At this tempo you can then record drums in double-time (124 BPM) and be at a dance tempo! (Once you decide on your remix target tempo, if your computer is running short on processing power, your can set the Elastic Time plug-in to Rendered Processing.)
step 10

Here’s what the final results sound like, using all of the stems at 62 BPM, some effect processing, and backed by Digidesign’s Strike virtual drum instrument playing in double-time at 124 BPM:
Nude – The Strike Remix (by Erik Hawk)