MOTU MIDI Express XT [82/94] Two forms of time code ltc versus vitc

APPENDIX B: TIME CODE BASICS

developed for ﬁlm and video work but has proven to be

very useful in normal audio work as well. It is an absolute

time code, expressing hours, minutes, seconds and

divisions of a second in digital form.

Because of its accuracy and wide-spread acceptance,

SMPTE is the most powerful of the time code formats that

are used in audio production.

TWO FORMS OF TIME CODE: LTC VERSUS VITC

SMPTE time code consists of a series of binary impulses

that are recorded onto each frame on ﬁlm or video tape, or

continuously on audio tape. These binary impulses count

each frame, expressing its location in hours, minutes,

seconds, and frames.

SMPTE time code has two forms:

1. an audio signal, called Longitudinal Time Code (LTC),

2. a video signal recorded in the vertical blanking segment

of video frames, called Vertical Interval Time Code (VITC)

WHAT IS LTC?

Longitudinal Time Code (LTC) is the audio form of

SMPTE Time Code. LTC consists of an audio signal that

oscillates between two frequencies (approximately 2 and 4

kHz) to form an 80-bit word of 1’s and 0’s for each frame

on the tape. The 80 bits in each SMPTE frame describe, in

binary form (1’s and 0’s), the location of that frame in

hours, minutes, seconds, and frames.

WHAT IS VITC?

Vertical Interval Time Code (VITC, pronounced “Vit-see”)

is SMPTE time code that is encoded in the video signal in

the vertical blanking segment at the top edge of each

frame. A video signal consists of 525 scan lines, which the

rotating heads of a VTR scan as the tape rolls past them.

The ﬁrst couple dozen of the scan lines at the edge of each

frame are blank; they do not contain any part of the video

picture. VITC is recorded on several of these blank scan

lines.

!USB Interfaces Manual Book Page 82 Tuesday, August 16, 2011 11:21 AM