MACKIE HDR24/96 - Manual (Page 202)

HDR 24/96
alternating between using three and two video fields (not frames) per film frame in a process called
2:3 pull-down, as shown in the illustration below.
So what does this have to do with digital audio? Well, audio recorded on location is synchronized to
the camera that is rolling at 24 fps. When the location recordings are brought in to the audio post
production process, they need to be pulled-down by the film pull-down ratio to remain in sync with
the picture (now in NTSC color video). While this 0.1% pull-down does not perceptively (to most
listeners) change the pitch of the sound, a 0.1% mismatch in rates will cause sync drift fairly quickly.
Therefore many digital audio devices support the ability to run at a pulled-down sample rate.
A similar Telecine pull-down process is sometimes used for 50 Hz video (PAL and SECAM) formats,
but because of the existing integer relationship between video and film frames, the Telecine process is
most often done as a real-time interleaving process (i.e. no pull down is involved). Thus
PAL/SECAM pull-ups and downs are much less used than NTSC pull-ups and downs.
Occasionally location audio is pulled up so that after the Telecine it runs at a standard Sample Rate.
For example, when a music video is made, sometimes the director will have the artists lip-sync to the
original song playing back at a pulled-up rate, so that when the film is transferred to video for
television broadcast, the music will get pulled down to the original sample rate at which it was
recorded.
Fortunately the need to use pull-ups or pull-downs only arises when working with location recordings
for theatrical film, when synchronizing to certain digital video machines (that support digital audio),
or when otherwise directed to do so by the technical director of a film for purposes of standardizing
the post production process. Most of you can breathe a sigh of relief. For those of you who must use
pull-ups and pull-downs, here is how they work.
For each standard Sample Rate, a pull-up and pull-down sample rate is defined for both NTSC and
PAL/SECAM. In version 1.1 the HDR24/96 will support both NTSC pull-up and pull-down sample
rates, but not PAL/SECAM pull-ups/downs. The standard Sample Rates and their corresponding
pull-up and pull-down rates are as follows:
50.0 kHz PAL/SECAM pull-up
48.048 kHz NTSC pull-up
48.0 kHz Standard rate
47.952 kHz NTSC pull-down
46.080 kHz PAL/SECAM pull-down
45.9375 kHz PAL/SECAM pull-up
44.1444 kHz NTSC pull-up
44.1 kHz Standard rate
44.056 kHz NTSC pull-down
42.336 kHz PAL/SECAM pull-down
HDR 24/96 202