Ensemble Designs BrightEye 5 Analog Composite TBC and Frame Sync - Manual (Page 26)

www.ensembledesigns.com BrightEye 5 - Page 26
5 Analog Composite TBC and Frame Sync User Guide
Setup
In the NTSC Analog Composite standard, the term Setup refers to the addition of an artificial offset
or pedestal to the luminance content. This places the Black Level of the analog signal 54 mV (7.5 IRE)
positive with respect to ground. The use of Setup is a legacy from the early development of television
receivers in the vacuum tube era. This positive offset helped to prevent the horizontal retrace of the
electron beam from being visible on the CRT, even if Brightness and Contrast were mis-adjusted.
While the use of Setup did help to prevent retrace artifacts, it did so at the expense of dynamic range
(contrast) in the signal because the White Level of the signal was not changed.
Setup is optional in NTSC systems, but is never used in PAL systems (see ‘Perfection’ characteristic of
PAL). This legacy of Setup continues to persist in North American NTSC systems, while it has been
abandoned in Japan.
In the digital component world (SD and HD SDI) there is obviously no need for, and certainly every
reason to avoid, Setup. In order for the interfaces between analog and digital systems to operate
as transparently as possible, Setup must be carefully accounted for in conversion products. When
performing analog to digital conversion, Setup (if present) must be removed and the signal range
gained up to account for the 7.5% reduction in dynamic range. And when a digital signal is converted
back to analog form, Setup (if desired on the output) must be created by reducing the dynamic range
by 7.5% and adding the 54 mV positive offset. Unfortunately, there is no truly foolproof algorithm to
detect the presence of Setup automatically, so it’s definitely a case of installer beware.
SDI
Serial Digital Interface. This term refers to inputs and outputs of devices that support serial digital
component video. This could refer to standard definition at 270 Mb/s, HD SDI or High Definition Serial
Digital video at 1.485 Gb/s, or to the newer 3G standard of High Definition video at 2.97 Gb/s.
SMPTE
The Society of Motion Picture and Television Engineers is a professional organization which has done
tremendous work in setting standards for both the film and television industries. The term “SMPTE’” is
also shorthand for one particular component video format - luminance and color difference.
Single Mode
A Single mode (or mono mode) optical fiber carries an optical signal on a very small diameter (9
micron) core surrounded with cladding. The small diameter means that no internally reflected
lightwaves will be propagated. Thus only the original “mode” of the signal passes down the fiber.
A single mode fiber used in an optical SDI system can carry a signal for up to 20 kilometers. Single
mode fibers require particular care in their installation due to the extremely small optical aperture that
they present at splice and connection points. See also Multi-mode.
TBC
A Time Base Corrector is a system to reduce the Time Base Error in a signal to acceptable levels. It
accomplishes this by using a FIFO (First In, First Out) memory. The incoming video is written into the
memory using its own jittery timing. This operation is closely associated with the actual digitization of
the analog signal because the varying position of the sync timing must be mimicked by the sampling
function of the analog to digital converter. A second timing system, genlocked to a stable reference,