Join Brian Lee White for an in-depth discussion in this video Understanding Elastic Audio, part of Pro Tools Projects: Time Manipulation with Elastic Audio.
Fully integrated Elastic Audio was introduced in Pro Tools version 7.4 and is easily one of Pro Tools' most powerful Editing tools. Want to automatically speed up the tempo of an imported audio loop to match the session without changing the pitch? That's Elastic Audio. How about quantizing audio recordings as easily as if they were MIDI? Elastic Audio again. Maybe even find the perfect pocket between your kick drum and bass. That's Elastic Audio. What once would have been deemed impossible, Elastic Audio allows users to stretch or shrink slices of audio directly inside the Edit window, effectively slowing down, speeding up or changing the rhythmic feel of an existing recording, all while preserving the original pitch.
So when I think about the origins of time manipulation, I think back to tape and vinyl. How DJs could slow down or speed up records to match the tempo of the previous song or how you could speed up or slow down the tape playback. The problem with this is while it changed the tempo, it also changed the pitch. Because in a medium like vinyl, the grooves actually represent the waveform oscillations and waveform oscillation is directly related to pitch.
So when you play it back faster, it's pitched up. If you play it back slower, it's pitched down. So the origins of Elastic Audio style processing in Pro Tools actually came a lot earlier than the built-in Elastic Audio system. We have the AudioSuite plug-in under Pitch Shift > Time Shift which allows us to select an offline processor region to be faster or slower. This actually analyzes and then renders a new file offline, preserving the pitch of the audio, making it faster or slower, but the problem with this is it's really hard to manipulate in context with the rest of your song.
You had to do this offline. It created lots of files. Now a little later on, they developed the TCE Trimmer tool and the TCE Trimmer, if I just click and hold on the Trim tool, it says Time Compression Expansion, this actually ties to that plug-in I just showed you and I can stretch or shrink making things slower or faster and I could even cut up little portions of a region to shrink or stretch and again originally, how this was implemented, it was tied to the AudioSuite plug-in.
So when you stretched something, it actually would go into the plug-in and re-render a new region in your regions list. So there was still some processing time. It was a little bit more elegant than actually selecting and configuring parameters because you had an Edit tool but it's not nearly as elegant as the Elastic Audio system is today. So regardless of Elastic Audio today, or using these TCE Trimmers or AudioSuite tools, how this basically works is that audio is manipulated by analyzing an audio recording's content, isolating the rhythmic transient portion, the highest point of amplitude in the region, versus the sustain and decay portions of the sound.
Now this algorithm effectively determines how samples of the audio can be duplicated or removed to stretch or shrink the passage, thereby increasing or decreasing the tempo or even changing or what we call warping in the rhythmic feel in the context of the adjacent audio. Remember, because pitch is directly related to waveform oscillation, simply playing back the samples at a different speed is not enough. In order for the pitch and timbre of the original recording to stay intact, the algorithm must account for these things when deciding what to add or subtract.
So just to give you a basic example of what's going on at the heart of this, if I copy a little piece of this bass here and paste it out so we can look at it over here and I really zoom in on that so that I can see the waveform oscillation. You see there is a repeating pattern that's happening for that sustaining bass note. So we have the transient that happens here. It's a little bit different and then we have the final decay pattern here. Now if I were to go in and sort of match up like bookends a repeating oscillation or a group of repeating oscillations, and I were to let's say switch to Shuffle mode and either duplicate or delete portions, I could effectively increase or decrease the overall size of that note, effectively changing its speed but because I'm taking these small little windows out or adding windows back in, I am maintaining the original shape and thus pitch of the waveform.
While there may be a little bit more analysis magic to this than I just demonstrated, that is the basic idea of pitch-preserved time compression or expansion and these concepts form the basis of the Elastic Audio system in Pro Tools. So instead of just repeating one cycle, Elastic Audio algorithms may choose many slicers or what are sometimes referred to as grains to add or subtract from the sustaining portion of the sound. This is very similar to the concepts behind granular synthesis. So you may hear the term granular re-synthesis of sound used in the context of Elastic Audio or time stretching.
Now with percussive elements, like these drums here, sometimes it is only necessary to manipulate the empty space or air between the strikes. As these instruments are primarily transient based, where you have a strike and then very little sustain, it's just going to be a reverb-tail or a short sustain of a tom drum or a cymbal decay. So as oppose to melodic instruments that actually have a sustained pitch,that identifies the rhythmic performance, in something like drums or percussion it's actually a lot easier to manipulate the timing just by manipulating the air or space in between here.
Now if this all seems a bit too complex, don't worry. In the next video, I will show you how Elastic Audio can be implemented in very basic yet effective ways that don't require much more than a drag-and-drop. Later on, we'll discuss the subtleties of the different approaches Pro Tools uses to manipulate time and pitch and dig into manual elastic tweaking where almost anything is possible.
- Enabling elastic audio
- Selecting an elastic audio plug-in
- Analyzing regions with elastic audio
- Manually adjusting timing with Warp Markers
- Transposing pitch
- Quantizing audio
- Locking bass to kick drum
- Warping vocals
- Adjusting elastic audio settings