Time Code In Digital Recorders; Frame Rates - Nagra Seven Operating Instructions Manual

TIMECODE (Hardware option part number 70 19185 000)
The Nagra Seven can be equipped with an internal time code system. The time code system in the Nagra Seven
corresponds to all the internationally recognized formats defined by the SMPTE and EBU. This manual does not
cover the generalities of the time code format as this is covered in detail in many other publications.
This section covers more of the global aspects of the time code system covering the following subjects:

Time code in digital recorders

Time code frame rates
The internal time code generator
Time code playback / conversion
Displaying time code
Time code recording
Time code in digital recorders
When time code was first introduced to audio recorders in the Nagra IV-STC back in 1984, the time code signal
was longitudinally recorded along the center of the analogue tape, and the official audio time code format
stipulated that the time code value recorded on the tape at any given time was coincident with the
corresponding audio so as to maintain inter-machine compatibility.
Time code in a file based digital recorder is managed in a totally different manner. At the start moment of a
given recording, the time code value at that instant is "calculated" by the time code system and this value is
known as the time code "stamp" and is recorded in the "header" of the broadcast wave file. This time code
value is calculated based on several criteria, namely the presently selected frame rate, the sampling frequency
in use, the duration of the pre-recording buffer and the time code mode (Time of day or not). During playback,
or post production this time code stamp is read and calculated as if it were a normal longitudinal time code
throughout the recording.
This explanation helps understand why certain common features used in longitudinal tape-based formats
cannot be used in a file based system. For example, the recording of external time code in the past was
relatively simple, the incoming time code was simply re-generated and put on the tape. Therefore, time code
jumps or changes were all copied "blindly". In a file based format, once the external time code has been
"grabbed" at the instance that the recording starts, the external incoming time code becomes "irrelevant"
until the end of the current recording, because no further time code is recorded until the next record start on a
new file. The time code during playback of the file is calculated from the time code stamp in the file header.
It is thus technically possible to playback a file and re-create time code at any frame rate irrespective of the
original recorded format. It is important to understand these basic concepts to avoid making mistakes while
using the time code system, and selecting the correct parameters for your recordings.

Frame rates

Time code frame rates that can be internally generated directly by the Nagra Seven are as follows:
23.976 fps:
24 fps:
25 fps:
29.97 fps:
29.97 df:
Chapter IV
High definition rate, and is most commonly used with high definition video cameras.
At this frame rate, the count is 0.1% slower than real time.
Standard frame rate for film. Also occasionally used for high definition video
production.
PAL Video Frame rate, generally the norm in countries with 50Hz mains frequency.
(Typically European countries)
NTSC color video frame rate. At this frame rate, the count is 0.1% slower than real
time. Used for production in NTSC countries (typically North America and Japan).
NTSC frame rate with drop frame. Drop frame is the compensation system used in
NTSC to match the standard 29.97 frame rate to real time. Used in television
production in NTSC countries. (typically North America and Japan)
64 March 2014