Notes About Formatting Tapes for Sync Playback
by Fred Ginsburg C.A.S.
Introduction:
As many of you are aware, when film shot at 24 fps or 30 fps is transferred to video
for post-production (electronic editing), the actual running time of the film is reduced
by one-tenth of one percent in order to compensate for the difference in frame rates
(frame lines) between cinematic projection and the continuous cathode ray scans of the
video medium.
Other than rare instances of "recreational" chemical abuse, this accounts for
the main reason that many rock videos are slightly out of sync.
In order to compensate for this speed reduction that occurs during the film to video
transfer, it is necessary to maintain a similar speed change in terms of our audio. That
means that the playback version of the music that talent lip-syncs to must be played back
on the shooting set one-tenth of one percent FASTER than the true speed
of the song that will appear in the finished (video) product.
Using a timecode Nagra for playback:
If you will be using a Nagra IV-STC stereo timecode reel to reel recorder as your
playback source, adhere to the following guidelines. Prepare an EDIT MASTER
version of your song with an accompanying SMPTE timecode of 29.97 non-drop frame. This is
the version of the song that you will use in the edit bay to cut your video to.
From the EDIT MASTER, prepare your PLAYBACK DUPES. The dupes should be
exact copies or mixdowns of the EDIT MASTER, with precisely identical 29.97 non-drop frame
timecode recorded onto each copy.
At the head of the song, there should be a series of timing beeps (or countdown intro)
so that the performers will be able to hit the first note of the song in unison. Record at
least a couple of song passes onto each playback dupe to save rewind time.
Make at least two or three physical tapes, in case a segment of tape becomes damaged or
recorded over during the shoot.
On the set, play back your dupe at the frame rate of 30 non-drop frame. This will have
the effect of speeding up your music by one-tenth of one percent in order to compensate
for the fact that your film footage will eventually be slowed down by that same amount.
The timecode from the playback Nagra needs to be transmitted via a Comtek wireless
system to the timecode slate, since the timecode numbers that we want to photograph need
to be the timecode of the playback tape, and have no relationship to real clock time nor
record start/stop time (as it would if we were doing live dialog recording for a motion
picture).
Make sure that when you order your Nagra that you indicate that you will be doing sync
playback, since the Nagra does not self-resolve without a special accessory box
(resolver/TCstripper) that must be added to your package, along with the Comtek
transmitter system for the timecode.
Using DAT for sync playback:
The use of portable DAT recorders for sync playback has become increasingly popular. If
you will be using a consumer or non-timecode DAT recorder, then it is necessary to prepare
your PLAYBACK DUPES with a monaural audio mix on one track and SMPTE timecode on the
other.
Consumer DAT's will only playback the tapes exactly as recorded, with no provision for
speed-ups nor slow-downs. Therefore, DO NOT make an exact replica of your EDIT MASTER for
sync playback.
Instead, arrange for the recording engineer to speed up the EDIT MASTER tape during
transfer to DAT, playing back the song one tenth of one percent faster, and re-generating
the timecode from 29.97 non-drop to the new value of 30 frame non-drop.
What you play back on the set must be the faster version of your song along with the
faster time-code rate! Again, think in terms of multiple passes of the song on each tape,
and multiple tapes in case of physical damage.
It will be necessary to transmit the timecode via Comtek to the slate, so make sure
that you have all of the required adapter cables.
Using timecode DAT for playback:
When using a more sophisticated DAT recorder such as the Fostex or HHB machines that
have timecode capability, it is essential to remember that tape speed and timecode speed
can be independent of each other in the DAT domain.
Tape speed is determined by the sampling rate, period! A DAT tape initially recorded at
48K and played back at 48.048K will reflect a one tenth of one percent speed increase, or
vice versa. However, the time code output will not change from 29.97 to 30.
Similarly, a 48.048K tape that is played back at 48K might still output timecode at the
30 rate. So make sure that the machine operator is familiar with the peculiarities of
his/her machine, and remembers to re-set both the sampling rate and the timecode output
rate to the appropriate settings.
If the PLAYBACK DUPE is an exact replica of the EDIT MASTER, we can assume that it is
recorded at 48K with a 29.97 non-drop timecode. Play it back on the set at 48.048K, with
the code reset to 30 frame non-drop.
If the DAT only does pull-downs (slow-downs), then transfer from the EDIT MASTER to the
slower 47.96K sampling rate, so that when you play it back at 48K the song will be speeded
up on the set by the proper percentage.
Determine whether or not the DAT machine in question automatically reconforms the
output timecode to match the speeded up rate or does it keep the original timecode. In
other words, does 29.97 automatically become 30, or not? Sound complicated? It is!
Very often, to eliminate confusion, the recording studio will format the PLAYBACK DUPE
for proper playback at 48K/30 frame non-drop with instructions for the playback operator
to not worry about pull-ups and pull-downs. But never assume. Ask. And ask again!
CD Playback:
A new process that we are developing is to prepare the PLAYBACK DUPE onto a writable
audio CD, with audio on one track and correct timecode on the other. Speed and timecode
changes are corrected during the transfer to CD, so that correct playback on the set is as
simple as selecting a track on the CD and pressing play.
The PLAYBACK CD will contain a complete version of the song, along with a number of
short excerpts for instant cueing.
ASK, BUT NEVER ASSUME:
The bottom line is that the version of the song being played back on the set must be
one tenth of one percent faster than the version of the song that the video editor is
going to use in the finished video.
In analog (reel to reel), that means that a song mastered with 29.97 non-drop timecode
will be speeded up by the playback Nagra on the set to 30 frame non-drop.
Conventional DAT and CD must be speeded up by the studio during transfer BEFORE the
tapes go to the set, so that when they are played back at their "normal"
settings, they will output a version of the original song that is faster and has 30 frame
non-drop timecode.
Timecode DAT demands attention to both speed and timecode changes during the playback
and/or transfer process, depending on the capabilities of the make and model of the DAT
recorder. Make sure that the operator is familiar with the machine and its programming
routines! Make sure that you are not double-dipping by changing the playback speed of a
PLAYBACK DUPE that has already been speed corrected by the studio. | 
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