Fixing timing errors with time compression/expansion
In the last article, I mentioned using a tool called TCE (time compression/expansion) to fix timing errors while editing an acoustic drum performance. This article will dive a little deeper into the technicalities of the practice - I know when I first discovered it, the quality of my recordings improved substantially. As a fair warning, this article will reference Pro Tools specifically, but I’m sure other major DAW’s have a similar capability.
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The Tool
The capabilities of Pro Tools TCE Trim Tool is defined by Pro Tools Expert as:
“Rather than trimming the clip boundary and concealing or revealing additional audio the TCE trim tool time stretches the audio to the new length. For new users this is an excellent tool for use with loops to conform audio to the session tempo.”
The way they describe to use it makes a lot of sense (and I do use it this way quite often). Let’s pretend you have a drum loop you want to use that’s at 88bpm but your song is at 90bpm - you could use the the TCE trim tool to change the bpm of the loop to match your song. The major difference between TCE and other techniques is it automatically accounts for the change in pitch that naturally occurs with shortening/lengthening clips with very few artifacts (i.e. lengthen a clip and pitch lowers, shorten and it gets higher).
To access the tool, click and hold the trim tool (white square with 2 arrows) in the top menu of the edit window, and select the version with the clock from the dropdown.
Traditional approach to fixing timing errors
Pro Tools beat detective tool is the default for fixing timing errors. Beat detective works by separating hits at each transient, moving each separated clip onto the grid and then fading the clips together to prevent artifacts. In my experience, this process has always ended up sounding noticeably edited and quite sloppy. Sometimes the clips overlap, sometimes there’s spaces, sometimes there’s clicks and pops - you get the picture.
How we use TCE
Instead of using TCE to fix full loops, here at Perch we use it as a new and improved version of beat detective. Here’s how to do it:
Turn on tab to transient (top bar, button underneath trim tool, looks like an arrow next to a waveform). Also make sure AZ is turned on in the rightmost edge of the screen (this turns on shortcuts.
Click into the audio track you are editing, hit tab then press D to make the cut. Repeat this process with all transients in the clip.
Go into TCE trim mode (instructions above).
Start at the end of the clips - drag the first (or last depending on how you think of it) clip onto the grid (make sure your in grid mode). Then use the TCE tool to drag it to the necessary length.
Use TCE to drag the next clip to the left so it goes right to the beginning of the last one you handled. TCE the front into place as well.
Repeat step 5 with the next clip.
The Benefits and Power users tips
The real benefit here is the waveform of the original performance is never broken - there’s no silence, no clicking and popping and very few artifacts. If you do need to make fades, I recommend going into the smallest grid mode possible around the cuts and using short fades on each clip right around the cut. You can even use the pencil tool to even out the waveform around the clip for more accuracy.
One way to improve the quality is to go into sample grid mode and instead of using tab to transient only, find the nearest sample beginning to a zero crossing point and make the cut there.
Gridding a performance sound too robotic? Try using a guide track and TCE’ing (yea, it’s a verb now) to that performance instead of the grid. You can even find a measure of the performance that really grooves and use that as a guide for the whole performance.
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While time consuming, this process drastically improves the believably of a performance while also fixing the timing errors. Feel free to try it on instruments besides drums as well - it tends to work really well on almost anything - vocals, guitars, pianos, etc. However, I’d be careful with long bass notes, as the artifacts become extremely noticeable.