When you import an audio file into a Pro Tools session you are presented with several options as far as its sample rate is concerned, and it is important to choose the right one if you want it to play back at the right speed. Although you can drag-and-drop audio files from the Finder and Workspace Browser, to have the most control over what happens when you import the file choose File > Import Audio (Shift-Option-i).
Adding a File
Pro Tools 10 has added support for files of multiple bit depth in the same session. You can also mix and match audio file types (.wav, .aif and .sd2, but not .mp3), but you will be given a warning if the sample rate does not match. If you choose to Add rather than Convert, an audio file whose sample rate does not match that of the session and click 'Yes' in the warning dialog that appears, Pro Tools will reference the original file location and play the audio at the wrong speed. For example:
- 44.1 kHz files in 48 kHz sessions play back too fast
- 48 kHz files in 44.1 kHz sessions play back too slow
Choosing 'Add' in the Import Audio dialog
You will be warned of the sample rate does not match
Copying and Converting a File
If the sample rate of the session and the file match, you will be able to add or copy the file. The second of these two options means that your session will reference a new copy of the file which is placed by default in the Audio Files folder of your session folder.
Choosing a file with the same sample rate as the session will show the Copy button
If the sample rate does not match, the 'Copy' button will be replaced by the 'Convert' button. When you choose this option the 'SRC' box (it stands for Sample Rate Conversion) will be ticked and the 'Source Sample Rate' drop-down menu will show the recorded sample rate of the chosen audio file. As you might expect, this box is not ticked when copying the file (sample rates match), but it can be, and as with 'Convert' the Source Sample Rate can be changed.
Choosing a file with a different sample rate as the session will show the Convert button
Changing the Source Sample Rate
Although there are other ways to do this (by time-stretching with the TCE Trimmer tool for example), you can change the speed of an audio file for creative effect by choosing a different Source Sample Rate. To illustrate how this would work here are some examples:
- Setting the Source Sample Rate to 22.05 kHz when importing an audio file that was recorded at 44.1 kHz into a session whose sample rate is 44.1 kHz will create an audio file that plays back at half speed.
- Setting the Source Sample Rate to 88.2 kHz when importing an audio file that was recorded at 44.1 kHz into a session whose sample rate is 44.1 kHz will create an audio file that plays back at double speed.
Choosing a different Source Sample Rate
Pull Up, Pull Down
The situation in which you would deliberately choose to change the sample rate on import is when 'pulling up' or 'pulling down' to cope with speed changes when converting from film to video or vice versa, and this will be the focus of the second part of this article.