When and How to Use Time Stretch or Pitch Shifting

Clarity on Oft-Misunderstood Timing Concepts

In a TBC (The BeatTips Community) thread about drums, core TBC member Castro Beats offered up a great breakdown of the differences between Time Stretch and Pitch Shifting. Below is Castro’s post, followed by my reply.
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I personally use Time Stretch when I’m doing Post production work (sound FX for movies) because it helps keep timing/pitch, but that’s the only time I really use time stretch/elastic audio. My “time stretching” is typically done on the MPC by Up pitching or down pitching whatever I have on the pads to meet a certain length or just change the sound. The only difference is that this isn’t really time stretching because it speeds up or slows down what you pitch. In Pro Tools/Cubase nowadays they have things like elastic audio, so you can create warp points (just like Recycle/Ableton) and it is able to adjust the loop to the tempo you set without changing the pitch. Depending on how far you go up or down with the tempo, the loop you’re stretching could sound right or real choppy. You might apply the elastic audio rhythm to a track in pro tools and be very pleased, till you pull the tempo down far enough that the kick happens then a second later the hi-hat etc.

Now that that’s explained, (I did so so everyone can understand what the difference is between time stretch and pitch shifting), Recycle has a similar but different style of time stretch. It’s more of “expanding the tails of your slices” then time stretching, because when you throw a sample in Recycle and create slice point and put it into a program like Reason, it uses the now longer tails to compensate for tempo adjustments. It doesn’t change the pitch it just helps match for timing in the event that you do alter the tempo. I only use that for two reasons, 1) corrective 2) the extended tail sound is cool. I personally want to hear the pitch alter the speed of the sample in most cases, not necessarily keep it at it’s original tempo. The flip side of the time stretch is that it works the other way too. Instead of stretching the tails, you can make the slices super tight by shortening the decay and turning the stretch to 0%. If you play the whole loop it will sound choppy, but the individual hits will sound on point.

The way the MPC pitch shifts is great because if you have ever tried to do this in pro tools, you know that you can only go so far or do it so much before the sound is now destroyed and riddled with artifacts. The MPC and programs like SoundHack do some of the illest pitch shifting handsdown, and that is how I handle my drums to fit. I have used elastic audio/warp point features before for samples and other things, but it’s more in moderation then anything else. I don’t like the idea of the tempo controlling the sample/sound like Patch Phrases. That is a really good feature, the Patch Phrasing on the MPC, but it’s only really useful when using the whole loop, something I don’t typically do. On the MPC I can pitch something down by -36 and be able to use it without it syncing to tempo. As far as making it sound unnatural, yes and no. If you timestretch then you can get it to sound like that same loop is being played at a slower/faster tempo. Which up to a certain point will sound very natural. But when you pitch shift, things can be slightly bigger/smaller hit depending on +/- pitch. If you do it excessively it can become a whole new sound which is something I totally support doing. I feel that Pitch Shifting should be applied to slices, and time stretching to loops. If you’re looking for natural you might as well sample an actual drum kit. Since I actually mic’d up a drum kit and did that, I can tell first hand that while those “real” drum sounds are great, specifically the smaller percussion (tambs, hats etc), it can become real “Eagles” sounding. Not much character, but definitely it’s own sound.

In short, there is a huge difference in time stretching and pitch shifting. I like to pitch shift for creative purposes, and time stretch for corrective purposes. At present I am good enough at chopping samples that time stretching is just a “dusty tool” in the toolbox as I find slicing/pitch shifting more effective for what I am doing.
—Castro Beats
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Here’s my reply

Castro,

Excellent breakdown! Bravo!!!
I particularly like your explanation for when, how, and why you use pitch shift and time stretch: “…pitch shift for creative purposes, and time stretch for corrective purposes;” and “Pitch Shifting should be applied to slices, and time stretching to loops.”

I certainly see the advantages to this approach. I’m sure that you probably even have found some ways to use time stretch creatively as well…
For me, I’ve practically never used time stretch on loops. I have, however, used it on various sounds that I wanted to elongate and sustain, but that’s about it.

One reason that I try to avoid time stretch, and instead rely more on tempo, is because of control. Part of my approach—especially when it comes to sequencing and arranging—is to try and *control* all of the musical elements that I use, in a way that encourages me to rely on my DJ background. Time stretch is certainly a great tool, and you’re are absolutely right, as far as correction goes, it can smooth out sound flaws and time issues.

When I went through my experimental phase with time stretch, I learned how to drag faster tempos and push (shuffle) slower tempos. However, I also soon figured out how to do the exact same thing, by doing things like modifying the tempo; re-recording certain sections of the drum framework with timing correct turned off; inserting elongated sound-stabs where the timing wasn’t quite right, etc.

Thing is, I never want my drums to sound perfect, I just want them to move and feel the way I envision. Also, I should mention that at the time when I was experimenting with time stretch, I didn’t know if I was on the right course or not. I just knew that I didn’t like relying on time stretch as some others did. Then I spoke to DJ Premier about it, and he told me the instances in which he liked to used time stretch. Since I was already using it similar to how he described his use of it, I continued my move away from it, as my drum frameworks had already taken on the sort of swing and shuffle that I like. Even still, if I’m making a beat and I believe that time-stretching something will be useful, I won’t hesitate to rock with it.

—Sa’id

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The BeatTips Manual by Sa’id.
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