Mackie 8-BUS Series, Руководство пользователя

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C-1
O w n e r ’ s M a n u a l
Synchronization
Appendix C
Synchronization
Synchronization is a topic that is often con-
fusing to the first-time user of multitrack
recording equipment, MIDI sequencers, and
automated mixing. The source of the confusion
is not so much in understanding synchroniza-
tion itself, but in understanding the various
types of synchronization that exist and how
they are used. This section details the various
types of synchronization and time code that
have developed over the years, where they
came from, and how they are used. We hope
that this short guide will help you better under-
stand how to use the Digital 8•Bus
automation.
What Synchronization Is For
“Synchronize,” as defined by Webster’s New
World College Dictionary , comes from the Greek
“syn,” meaning “together,” and “chronos,”
meaning “time for a nice cup of tea.” Basically,
synchronize means “to move or occur at the
same time or rate.”
Nothing magical here. In fact, synchroniza-
tion has been around as long as drums have
kept time to music. Keeping the beat so that
multiple devices can run at the same speed is
one of the primary purposes of synchronization.
Types of Time Code
There are two forms of time code that are
used primarily in the audio/video industry to-
day: SMPTE and MIDI. They both serve the
same purpose, to allow two or more machines
to lock to a common time frame. One source
serves as the
master , and all the others are
slaves . This means that the master generates
a time code while the slaves (other devices)
read it and follow along.
Types of Synchronization
You’ve probably heard of a “click track.” It’s a
prerecorded track with a series of evenly-timed
clicks that allow the musicians to play at a con-
sistent tempo. (Think of a metronome,
persistently—consistently—clicking away.)
When dubbing or overdubbing, the talent listens
to the click track in their headphones. This type
of syncing is called
pulse synchronization ; the
pulse signals convey the rate of speed (tempo),
but that’s all. In order for machines to be in
sync, they must start at the same time,
and at
the same point in the program.
A more complex synchronization method,
sometimes called timepiece synchronization , uses
place markers to identify the location of each in-
dividual pulse within the program. This allows
the machines in the system to sync to each
other even if they don’t start at the same time or
the same place in the program. In this case, the
slaves in the system chase to the location indi-
cated by the master, and then lock to it. SMPTE
is an example of timepiece synchronization.
SMPTE
SMPTE time code (pronounced “Simp-tee”)
was chosen by the Society of Motion Picture and
Television Engineers as the industry standard
for synchronization in 1971. The purpose of
SMPTE was to allow for editing of video tape. It
not only indicates tape speed, but also tape posi-
tion. A SMPTE time code generator produces a
continuous string of digital words that convey
timing information in the form of hours, min-
utes, seconds, and frames. This information can
be read back by a time code reader so that you
can find the exact spot in a film or video where
an event occurs, and edit the audio so it is per-
fectly in time with the picture.
The hours, minutes, and seconds used by
SMPTE are universal, but the frame rate and
number of subdivisions of each second differs
according to the application. There are four
frame rates primarily in use today:
30-Frame — 30 frames per second was the
original frame rate used by SMPTE. In the
United States, black-and-white video runs at 30
frames per second, which was derived from the
60-cycle AC line frequency.
30 Drop-Frame — When color television
came along, the frame rate had to be reduced
slightly in order to accurately reproduce the
color (29.97 frames per second, to be precise).
But by solving one problem, it created another.
The time code ran slightly slower, so that one
hour by 30 Drop-Frame standards actually
lasts one hour and 3.6 seconds. So a scheme
for periodically dropping frames was developed
to compensate for the time differential. 108
frames are dropped every hour, the equivalent
of 3.6 seconds worth. This is currently the
standard for U.S. network broadcast of color
television.
25-Frame — In Europe, the AC line frequency
is 50 cycles per second. The European standard
time code for both black-and-white and color
television is 25 frames per second. This applies
to any country that uses the 50Hz line reference.
24-Frame — The film industry uses 24
frames per second, so 24-Frame time code was
introduced to correspond to film.