Understanding
TIME CODE- part I
courtesy B&H PhotoVideo
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Time code
synchronization is still a big mystery for many audio
and video professionals, and as today's Audio and Video
technologies continue to integrate, having a basic
understanding of time code has become more and more
essential for both studio and field production. The good
news is that the basic principles are really
straightforward and easy to familiarize yourself with.
This technology isn't exactly cutting edge; it was
developed in the early Sixties to provide a kind of
"virtual sprocket" for frame-accurate editing of
videotape. |
Time code,
sometimes known as SMPTE (pronounced Simp-Tee) or SMPTE code, is
an electronic signal which is used to identify a precise
location in digital systems and on time-based media like audio
or video tape. SMPTE is an acronym for Society of Motion Picture
and Television Engineers, the developers of this standard. It is
used extensively for synchronization and reference throughout
the audio, video production, and post-production world.
A
SMPTE display looks like this:
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The
numbers represent: |
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(The
display above represents a Time Reference of 2
Hours: 1 Minute: 59
Seconds: 29 Frames)
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SMPTE uses the
same format as military time: the HOURS are
numbered from 00 to 23 hours, the MINUTES field
increments 00 through 59 minutes, and the SECONDS
field increments 00 through 59 seconds. Frames
represent a single image, the smallest increment which can be
cut. A frame is comprised of 80 bits of binary data called a
"time code word."
What is the
Difference Between LTC & VITC?
• LTC (for
Linear or Longitudinal Time Code) - Data is a series of
square waves recorded on an audio track of the "Master" device.
The synced device (referred to as the "Slave") reads that
timecode data from the "Master" and chases it. Because LTC is an
audio signal, the time code information cannot be read if the
tape is not moving.
• VITC
(Vertical Interval Time Code) - Data is encoded into
the blank "vertical interval" between video frames. VITC
information can be read when the tape is not in motion.
What is a
Frame?
There are several
varieties of Time Code used throughout the world. The two
variables that differentiate these consist of: the "Reference
Frequency" and the "Frame Count". The Reference Frequency refers
to the AC (alternating current) mains frequency: 60Hz (North
America, South America & Japan) or 50Hz (Europe, Asia, and
Africa). The Frame Count refers to the number of frames in one
second of time code. There are four methods of counting frames
with time code: Non-drop frame SMPTE, Drop frame SMPTE, 24 frame
SMPTE, and 25 frame SMPTE (EBU).
Every frame of
video has a time reference that is recorded together with your
video. "Time code" on a video tape is similar to the folios in a
book, and each page in a book is like a frame of video. A book
is made up of many pages, and a video tape is made up of many
frames of video, each having their specific frame of reference
in time, each with their own unique identifying number.
Syncing Your
Audio & Video
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One of
those "easier-said-than-done" tasks that video editors
face is the synchronization of audio to the video, for
example, blending the video and audio recorded by
multi-camera shoots, or adding the audio tracks from a
separate digital audio device. Because the DV format
compresses the audio to tape, many shooters prefer the
higher quality that recording to a separate digital
audio device offers. Although there are many digital
audio recorders with time code capabilities on the
market, for now let's assume you are using one without
time code. We will be taking a closer look at time code
audio recorders in a future Pro Audio Newsletter. |
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Time code is
written on the video camcorder and on the audio recording
device. To sync the time code that is generated in these audio
devices to the video source can be problematic. Editors
generally look for a point to reference within the video where
an audio spike has been generated that leads to the
synchronization of all the sources. These references could be
manifested as a person who claps their hands, coughs in the
scene, or a camera flash that goes off that has an audible tone
when it is fired. This is why a clap board is used to provide a
reference point to sync the audio to the video.
Time Code and
Your Camcorder
Experienced
videographers will "stripe" the video tape with time code prior
to their shoots. To prepare the blank tape to be striped, they
rewind the blank tape to its very beginning, and with the lens
cap on the camera, press Record and record black from the very
beginning to the very end of the tape. Striping the tape burns
time code to the tape, and this time code will not change when
recording your future video footage to that tape. This can
alleviate possible time code inconsistencies that can be created
by many types of camcorders.
What about
Consumer cameras?
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Consumer
camcorders record a time code, but it may not meet the
SMPTE standards, and may cause inconsistencies to the
time code recorded. For example, Sony consumer
camcorders record time code known as "RC time code."
And the various manufacturers of consumer digital DV &
HDV camcorders record digital "DV time codes". |
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You will find that
with these consumer camcorders, when you press Stop while
recording, your time will not reset to the correct time code
indicated in your last frame. The time code will revert to time
code reference 00:00:00. It cannot be reset manually with these
types of camcorders. (This is not to be confused with pressing
the Pause button intermittingly during recording.)
Helpful Tip:
Editors should
be aware of a few issues when transferring video to another
deck, device, or NLE computer system. The time code will not
transfer if you connect via analog video, composite RCA, S-video
(Y/C), component, or HDMI interfaces. Time code is carried
through iEEE1394 (DV), RS-422 protocol, or through a camcorder
that incorporates a separate time-code channel, typically with a
BNC connector. Time code is crucial, especially if you want to
do a "batch capture" with your NLE. Batch capturing is the
process of capturing selected clips from a recorded-on-source
tape, based on a log or shot list created by the user.
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Therefore, aside from being the
industry standard time code, SMPTE continues to deliver
the accuracy that all the editing software in the
industry demands. Professional camcorders like the
Canon XL-H1
are equipped with SMPTE time code inputs and outputs and
record time code continuously and chronologically.
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In the event that
your source video output does not carry the time code, a time
code generator can be connected between your video source and
destination. The time code generator creates a newly-generated
time code signal. Time code generators come in various
configurations to meet most applications.
A Quick Look
at Time Code Gear
B&H carries a large selection of SMPTE
time code equipment including: studio & portable
Time Code Generators,
Time code readers,
Character Inserters (also known as Window
"Dub" Inserters), and
Translators.
These devices come in various sizes and configurations to meet
every application. It is also important to know whether you are
working in NTSC or PAL system when selecting any of these units.
Time Code Generators
do just what the name says; they generate time code for video
and audio devices.
Time Code Readers
"read" and display the electronic time code signal. Many devices
do both.
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The
Ambient ACC-501
is a highly-accurate portable master clock and time code
generator/reader. It can jam, read, identify, and
compare all types of time code. This device supports all
frame rates and features crystal tuning, GPS time, and
an accuracy check function. This unit power via (6) "AA"
batteries. |
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The
Deneke GR-1
is a compact, precision master clock time code
generator/reader compatible with both SMPTE and EBU time
code. It supports frame rates of 24, 25, 29.97, and 30
fps, and its low-power LCD backlit screen displays the
incoming time code speed, user bits, and drop frame
status. |
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Character ("window dub") inserters
like the Horita WG-50 are used to produce work copies of
a master tape with the time code display "burned" into
the video picture. The WG-50 also acts as a SMPTE time
code reader and is compatible with all 1/2", 3/4", and
1" tape formats. |
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Translators
are used to convert one format to another, for example: LTC to
VITC or RS422 to LTC.
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The
Horita TCP-50
is a universal SMPTE/EBU LTC processor/translator that
translates between 24/25/29.97 and 30 fps LTC. It also
repairs damaged time code due to noise, dropouts,
missing information, etc. |
Multi-function devices like the
Horita VG-50
are designed to generate standard VITC time code in Drop-Frame
or Non-Drop-Frame format, and translate LTC (Audio) time code
into VITC time code.
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Tri-Level Sync Generators like
the
Denecke SB-T
are designed to provide reference in component and HD
applications. It generates Tri-Level Sync in all
1920x1080 & 1280x720 formats, composite PAL and NTSC, as
well as all standard time code rates, (including 23.976
for high-definition video). It improves accuracy by
providing a single crystal for referencing multiple
devices. |
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Large time code Reader/Displays are used
for film & video production in the studio and in the field. The
Horita TR-100
is an 8-digit large display that reads LTC and MIDI time code.
Deneke
makes a line of time code reader displays that have four
(TC MAXI/4)),
six
(TC MAXI/6),
or eight-digit
(TC MAXI/8)
displays. These large displays have an adjustable brightness
control to adjust display intensity for indoor use in a darkened
room or for outdoor use in bright light.
Time Code
Slates
Used extensively in the film and video
production world,
Time Code production slates
(also referred to as "Clappers") provide an identifiable audio
marker within a digital video or audio recording to synchronize
the sound of the clap with the picture at a specific time code
reference. Available in many different configurations, time code
slates can act as a readers, writer/ generators, and clappers
(with the option of wired or wireless operation).
Denecke production slates are designed for
a variety of budgets and applications. These affordable
production slates are available in color or black & white
versions, and two different sizes. The compact
TS-C
(color) &
TS-BW
(b&w) reads, generates, and displays SMPTE/EBU time code and
measures only 5" x 8.25" x 1.24". The TS-3 (color) & TS-3BW are
larger slates that measures 8.25" x 11" x 1.3". All of these
slates power via (6) "AA" batteries.
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Ambient Audio's
ACD301RF
Master Radio Slate generates and reads time code and
provides a large visible display with four different
display modes. This wireless slate has an internal
real-time clock to generate time of day for start-up and
can read or generate external code in the display. With
the push of a button, user bits can be displayed from
external or internal time code sources, frame and frame
rates, and time code errors can be checked without
jamming. |
This article was
meant to be a basic primer about time code, and by no means the
last word on time code or time code products. We will be getting
into more detail in future newsletter articles.
