Appendix I: Audio Time Compression and Expansion

Appendix I: Audio Time Compression and Expansion

Since the inception of digital audio, engineers and users alike have searched for ways to manipulate audio files in order to “play” them at different tempos without a shift in pitch (which was not possible with tape-based audio). The earliest methods for accomplishing this were, made commercially available from Propellerhead (Recycle), Spectrasonics (Groove Control) and Sonic Foundry (Acid), were useful, but did not actually use time compression or expansion (TCE). Instead, they separated audio files at the transient, grouped the separated regions so that they were perceived as one unit by the user, and associated a MIDI note with each component region. Then, because MIDI can be time stretched without pitch artifacts, the MIDI notes could be manipulated to fit a new tempo and to trigger the associated regions—a very clever method to solve a complicated problem.

1. 
   Enabling Elastic Audio on a track using the Conform to Tempo Command
   
   1. 
      Create an audio track
      
   2. 
      Set the Time Base selector to Ticks.
      
   3. 
      Click the Elastic Audio Plug-in Selector button (on the track header) and choose an appropriate plug-in
      
   4. 
      Place an audio region on the track. The audio region will go offline briefly as the region is analyzed.
      
   5. 
      Select the region and then from the Region menu select Conform to Tempo.
      

Example: Track Header

Track View

Selector

Time Base

Selector

Real-Time or

Elastic Audio Rendered Processing Indicator

Plug-in Selector

2. 
   Viewing and Editing Elastic Audio in the Edit Window
   
   1. 
      There are two new ways to view audio in the Edit window.
      
   2. 
      Select Analysis or Warp from the Track View Selector
      
   3. 
      Analysis view
      
      1. 
         After Pro Tools analyzes an audio file, an Event marker is placed at each detected transient. Event markers mark places in the audio file where the audio can be quantized or the audio can be stretched or contracted (Warped).
         
      2. 
         Switch to Analysis view to see and edit Event markers.
         
   4. 
      Editing event markers
      
      1. 
         Adding Event Markers
         
         1. 
            Click a location with the Pencil tool or…
            
         2. 
            Double-click a location with the Grabber tool
            
      2. 
         Move an Event Marker
         
         1. 
            Drag an Event marker with the Pencil or Grabber tool
            
         2. 
            Select one or more Event markers with the Selector tool and press the Delete key.
            
      3. 
         Delete an Event Marker
         
         1. 
            Option-click an Event marker with either the Grabber or Pencil tool
            
         2. 
            Select one or more Event markers with the Selector tool and press the Delete key.
            

5. 
   Warp view
   
   1. 
      In Warp view, Warp markers can be added to event markers. Warp markers can then be moved to stretch or contract audio between Warp markers.
      
6. 
   Creating and editing warp markers
   
   1. 
      Automatically adding warp markers
      
      1. 
         Place an audio file on a tick-based audio track with elastic audio enabled.
         
      2. 
         Select the audio region and quantize it.
         
   2. 
      Manually adding Warp markers
      
      1. 
         Switch to Warp view
         
      2. 
         Click an Event marker with the Pencil tool or
         
      3. 
         Double-click an event marker with the Grabber tool
         
   3. 
      Moving Warp markers without warping audio
      
      1. 
         Control-click and drag a Warp marker using either the Pencil or Grabber tools.
         
   4. 
      Deleting Warp markers
      
      1. 
         Option-click a Warp marker with either the Grabber or Pencil tool
         
      2. 
         Select one or more Warp markers with the Selector tool and press the Delete key.
         

Example: Event and Warp Markers (Warp view)

Warp Markers Event Markers

3. 
   Quantizing Elastic Audio
   
   1. 
      Select a region(s) on a tick-based, elastic audio-enabled track
      
   2. 
      Select the Event menu > Event Operations > Quantize (Option-3)
      
   3. 
      Select Elastic Audio Events (in the What to Quantize section)
      
   4. 
      Select a rhythmic increment or groove template as the quantize reference
      
   5. 
      Set other options desired and click apply.
      
   6. 
      In Warp view notice that Warp markers have been added to each event marker.
      
4. 
   Conforming or Rendering Elastic Audio
   
   1. 
      Real-time elastic audio places great demand on CPU resources, so, once an audio file has been conformed to a session tempo and edited as necessary, any elastic audio can be rendered as new audio file and region.
      
   2. 
      Click the Elastic-Audio plug-in selector menu
      
   3. 
      Set the Elastic Audio plug-in to “None-Disable elastic Audio”
      
   4. 
      In the Commit Dialog box, click the Commit button; this will render a new audio file(s) and reduce CPU useage.
      

1. 
   Enabling Flex and Generating Transient Markers
   
   1. 
      When Flex View is enabled, all audio track headers show the Flex Mode selector, which defaults to Off (no Flex). Choosing a Flex Mode enables Flex for all regions on that track, and each region is analyzed for transients. Logic places a light gray transient marker at each found transient.
      
   2. 
      When an audio file or region is placed on a track where Flex is active, that audio is immediately analyzed for transients and the transient markers appear.
      
   3. 
      To disable Flex for specific regions on an enabled Flex track, select the region and un-check the Flex checkbox in the Region Inspector.
      

Example: Track Header