AUDIO PULLUP and PULLDOWN

Frame Rates

The are several frame rates that you will come across in the post production world.
The most common ones are 29.97(NTSC), 23.98(NTSC), 24(Film), and 25(PAL).

When a picture gets transferred from one speed to another the audio will have to change speeds as well (**Note: this is not always true now with some advanced video transfers, but for the sake of this tutorial I will assume traditional speed changes are taking place)

29.97fps and 23.98fps are both slowed down .1% from real time (from 30 and 24 fps respectively). This means that 1 hour of timecode is actually .1% longer than an hour of real time.  This gave birth to drop frame timecode which is used in television. I will not go into drop frame here.

PAL and Film run at the same speed as real time.  That means that an hour of timecode will equal an actual hour.

The table below shows the speed changes between the different frame rates. (please note: all PAL conversions in this tutorial assume that the picture department plays 25fps picture at 24fps or visa-versa. There are other ways to convert PAL to NTSC and PAL to Film that do not incur a speed change)

Example     Film -> NTSC

To do pull ups and pull downs in Pro Tools we use the Sample Rate Conversion (SRC) feature on the import audio window. For our examples we will assume your source and destination are all going to be 48k.

1. Make a new session at the bit depth you are working at.  In the session setup window (command – 2 on the number pad) change your frame rate to 24.

2. Open the import Audio Window (shift-command-I) and choose the file you want to pull down.

3. Press the convert button, and check the box that says “Apply SRC” this will enable the “Source Sample Rate” dialogue.

4. Scroll to the bottom of the “Source Sample Rate” dropdown and you will see a category that says “48kHz (Pull Up/Down) Choose the appropriate setting which in this

case is “47,952 – 0.1% Down (film to NTSC)”

 5. Click Done and it will ask you where to save the file, and then it will import into your session.  You know have a file that is 48k, but plays .1% slower than the original.

Throwing PAL into the mix! PAL to Film Speed

Here it get’s a little more complicated.  Before you can do the conversion you have to take off any head or tail pops.  So cut your mix to first frame of action and last frame of action (when appropriate).  Then take that file and follow the steps below.

1. Make a new session at the bit depth you are working at.  In the session setup window (command – 2 on the number pad) change your frame rate to 24.

2. Open the import Audio Window (shift-command-I) and choose the file you want to pull down.

3. Press the convert button, and check the box that says “Apply SRC” this will enable the “Source Sample Rate” dialogue.

4. Scroll to the bottom of the “Source Sample Rate” dropdown and you will see a category that says “48kHz (Pull Up/Down) Choose the appropriate setting which in this case is “46,080 – (PAL to Film)”

5. Click Done and it will ask you where to save the file, and then it will import into your session.  You know have a file that is 48k, but plays 4% slower than the original.

6.  Now you will have to pitch your files up 4% to make up for the speed change. (Note: this is only done with 4% changes as a .1% change is not audible)

7. Add head and tail pops back on the file, and you’re all set to play you PAL audio at film speed!

The only time I suggest cutting off the 2 pop is when doing a 4% or 4.1% change. In this case the pop will not line up with the picture 2 pop because it will be longer than 2 seconds before the picture. I suggest cutting to FFOA because that is the only absolute reference point after the speed change.  At least the pictures I have gotten don’t have the visual 2 pop (or rather the space between the 2 pop and FFOA) changed 4% as well.

When doing a .1% changes the 2 pop is still relevant and I definitely keep it.

NOTE: When importing audio into Final Cut watch READ THE FOLLOWING:

If you are working on a project cut in FCP at TRUE 24fps (i.e Animation, or for finishing on Film via Cinema Tools) and you have exported you mix as a .WAV or .aif at that framerate… FCP puts a timecode value on audio it has imported. This value is the fps in the default capture settings -regardless of the fps of the Sequence. On most systems this will be either 29.97 or 23.976. However when you add this to a 24fps sequence FCP decides “Oh this audio has been pulled down, therefore I must pull it up to match with the 24fps timeline” – even if the audio is synced to a 24fps timeline originally. Yes, this includes BWAV files output from PT. The result is that the audio, which matches perfectly your QT movie in PT, and even in QTPro will play out of sync in FCP. Yes you read that right… FCP WILL pull up your audio without asking! So how do we work around this?

1. Have your editor make sure his default capture setting is the same framerate as his Sequence (good luck with this one…)

or

2. In QTPro, export your .aif as a .mov with the correct frame rate.

or

3. Use the Sebsky tools bwf2qt function to export an FCP movie with the correct framerate.

cheers

geo