Tuesday, November 20th, 2018

Warping Audio in Pro Tools 10

By Nick LucasSeptember 6, 2012

DAW WORKSHOP

Nick Lucas
Nick started out producing Drum & Bass and other Dancefloor styles under the pseudonym Veranova, still a major part of what he does.  Nowadays though, he also does a lot of Freelance work: composing for companies such as Morphsuits and producing music for the likes of Lewis Mokler, and Pob.  His most recent venture however, is Production Bytes, a web tutorials series aimed at Beginner & Intermediate level producers, which has led him straight into his passion for teaching and writing.

Let’s say you’re recording an artist for a record label, and you have one instrument which is out of time with the rest of the song.  The band has gone home and you don’t have the instruments available to re-do anything yourself.  But what’s worse, is you need to have the recordings mixed and finished by the next morning!

So you need to reach for your DAW’s tools to tighten up that performance…  This is where Pro Tools’ timing correction tools come into their own.

Here’s the project I’m going to be working with.

I’ve kept this simple for the purposes of demonstration.  Track 1 is a Drums Loop, and Tracks 2 & 3 are my two Mic’s containing acoustic Guitar.  I also have my Master fader and a Click track (a useful track to have for reference when adjusting timing).

https://www.audio-times.com/audio/Warping in Pro Tools Initial Project.mp3

You can hear straight away listening to this that the Guitar has plenty of timing discrepancies, and the Drums have some ‘Swing’.

The swing is okay as it adds some groove to the track and is controlled, so I’m going to work around that and focus on the Guitar.

Preparing for Time-warp

There are two ways to correct time discrepancies in Pro Tools.

Firstly you have Beat Detective (a subject for another time), which chops up audio into slices and allows you to move each slice onto a grid.  This is best for Rhythmic material such as Drums where the sustain phase needs to be kept the same length.  However it can create silent space after a hit before the next hit starts, once each slice is moved onto the grid.

For acoustic Guitar on the other hand, the sustain of the instrument is vital, and the realism will be impacted by sudden silences and cross-fading effects.  This is where audio ‘Warping’ comes in. Instead of slicing up audio, Warping allows you to stretch it wherever you like to bring sections into time.

To prepare your audio for Warping in Pro Tools, you need to switch on Elastic Audio for each audio track.  Do this by clicking the greyed out box under ‘Dyn’ & ‘Read’ on the audio track.  When you select Elastic Audio, you’ll be presented with a number of stretching algorithms.  Polyphonic is the best starting point for guitar, but they’re all fairly self explanatory [See ‘Cracking the codes’].

Cracking the codes

  • Polyphonic is designed for Instruments with more than musical note playing at once (Eg. Guitar, Piano)
  • Rhythmic works a little like Beat Detective by chopping up the audio so it doesn’t have to be stretched, and is best for instruments like Drums. It’s less powerful but more automated than Beat Detective.
  • Monophonic is best for instruments with only one musical note playing at any time (Eg. Bass)
  • Varispeed is slightly more unique, in that is doesn’t correct the pitch of audio when it’s stretched. If you shorten a section using warping the pitch will rise, and if you lengthen it the pitch will drop.  Just like analogue tape or vinyl speeding up & down.
  • Lastly X-Formed is an advanced Algorithm which takes so much CPU to process that it has to render the audio before playback instead of processing live. I’ll usually switch to this for my final renders, but do my warping work in Polyphonic mode.

 

To save yourself some time when switching Elastic Audio on with multiple tracks, you can switch multiple tracks in one go.  Select all the tracks using Shift+Click (For runs of tracks) or Ctrl+Click [Cmd+Click Mac] (For individual addition to/subtraction from the selection), then hold Shift+Alt [Shift+Option Mac] and select the Algorithm you want to use as normal.  This will switch all the selected tracks at once.

Finally switch all your tracks from ‘Waveform’ view to ‘Warp’ view.  Again you can do multiple tracks in one go using the previously mentioned shortcuts.

You’re now ready to start warping!

Stretching Time

You’ll see that all your waveforms have changed and should have lines (‘Elastic Audio Events’) on the transients.  Don’t worry if Pro Tools hasn’t detected every transient or has added some extra Events though, this does happen.

If you activate the Smart tool now, you’ll see that when you mouse over an Event your cursor changes and you can drag it around.  Double click and the line will solidify, creating a ‘Warp marker’.  Warp markers are permanent anchor points, and won’t be moved unless you move them, whereas Events can be moved by other adjustments you make; even if you’ve moved them yourself. 

Before I move on to Warping technique, there is an important process to use when dealing with Multi-track (Multi-mic) recordings.  Since each Mic’s positioning will be different, the waveforms will be slightly different in each audio clip.  Therefore the Events can be detected in slightly different relative locations, and if you warp each Clip separately this can create timing and phase issues between the Clips.  To get around this you can warp every audio track exactly the same, simply by grouping them.

To group the Audio Tracks, select the Tracks and press Ctrl+G [Cmd+G Mac], then selecting ‘Edit’ under ‘Type’.  Now anything you do to one clip in the group will also be done to the others.

I would suggest that good practice is to start by anchoring your audio clip at the start and end, so create warp markers on the first and last beats, but don’t move them yet.  If you move a point before anchoring your audio, you can get a ‘Telescopic warp’ where the whole waveform is stretched uniformly, sending it all out of time.  So first of all anchor your start and end (at very least to feel safe), and then start Warping the rest of the audio.

An example of a telescopic warp, the bottom track is the original audio

Here’s where the process starts to fragment. You’re ready to actually Warp your audio, but you can either have Pro Tools Quantise the Events automatically, or go through and manually move the Events you feel need shifting, or of course use a combination.

(If you want to work manually then jump ahead to ‘Fine tuning & Manual Warping)

Quantisation

Select the audio clips you want to warp and press Alt+0 [Option+0 Mac] to bring up the Quantise window.

For basic use there are only 2 settings you need to worry about:

  • ‘What to Quantise’ should be set to ‘Elastic Audio Events’
  • The ‘Quantise Grid’ option will allow you to select the time resolution that events will be warped to.
    • You may need to use some trial and error to find what works best for your methods. But for me in this case I just use 1/4 notes as I only want to Quantise the on-beats.
  • If you want to Quantise gently you may also be interested in the ‘Strength’ control.  This determines how much Events are moved towards their closest grid line.
    • 100% will snap the events directly onto the Grid, and
    • 0% will not move them at-all.
    • ‘Strength’ is therefore useful for tightening up performances without totally removing their life.

Once you’re happy with your settings, hit Apply and you’ll see your audio has had Warp markers added and quantised automatically.

Fine tuning & Manual Warping

Have a listen through to the Audio against either the song or click track (it’s personal preference, but remember you’re only aiming to get the audio to fit the final Song, which may not be totally rigid itself).

  • Markers can be moved ‘Relative’ to the Grid (adding or subtracting your current grid resolution to the current position) or ‘Absolute’ (Snapping the Marker) to the grid.
    • To switch between these press F4 to toggle between ‘Grid’ & ‘Relative Grid’ ‘Edit Modes’ (The 4 switches in the top left of the audio windows are the ‘Edit Modes’)
  • If any Markers don’t sound quite right to you can Ctrl+Click [Cmd+Click Mac] on them to finely tune them.
    • You can also do this with the Nudge controls on your num-pad by dragging a selection around the Warp marker first.
  • To remove mis-detected markers, you can simply Alt+Click [Option+Click Mac] on them.
  • To add warp markers you can double click on an event.
    • To Insert a warp marker where there’s no Event, use Win+Click [Ctrl+Click Mac].
  • If you’re warping from scratch it may also be useful to Shift+Click which creates 3 markers around the event you click on, very handy!

 End notes

Last of all, just continue the process of listening and tweaking until you’re happy with the timing.  I’ve explained the functions and basic techniques.  But you now need to learn the Skills, which means practice!

When done you can switch to a Rendered Algorithm (The same way you selected the Polyphonic Algorithm) to reduce CPU usage or increase quality, or go ahead and Bounce or Render the audio  for whatever you want to do with it next.

I’ve also included a finished audio file and the Project files below for you to play with.

Nick Lucas
September 2012

Listen to the finished audio: 

https://www.audio-times.com/audio/Warping in Pro Tools Final Project.mp3

Download the projects and have a go yourself: Warping in Pro Tools (7.6MB zip file)

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