Understanding TIME CODE- part I

By Robert Morton & Jack Fettman

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:
The numbers represent:
(The display above represents a Time Reference of 2 Hours: 1 Minute: 59 Seconds: 29 Frames)

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

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?

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".

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.

	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.

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.

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.

	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.

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.

Translators are used to convert one format to another, for example: LTC to VITC or RS422 to LTC.

	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.

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.

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.

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. For more detailed information on time code and time code equipment, we encourage you to contact us on the phone, online, or in person at our SuperStore in New York City. 1-800-947-1186

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