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RE> [TIG] What is Legal?



RE> [TIG] What is Legal?
To "Bill Topazio" <bt at mte.com>, "Brian Doros" <Brian_Doros at mte.com>, 
   "Chris Doros" <chris_doros at mte.com>, "Dave Corbitt" <dc at mte.com>, 
   "telecine group" <telecine at xyzoom.alegria.com>


Does anyone have specs on what the various transmitters in
use can handle?  This would be agood starting point, no?

--------------------------------------
Date: 5/21/96 8:09 AM
To: rterpilowski
From: "Dave Corbitt" <dc at mte.com>

                      Subject:                             
Time:  10:11 AM
  OFFICE MEMO         What is Legal?                       
Date:  5/20/96

Fellow TIG members,

I think SMPTE, the EBU, and our Post Production industry
need to come up with
guidelines and recommended practices for exactly what
constitutes "LEGAL" for
recorded video signals be they on a D-1 or Composite format,
525 or 625.  It
appears some facilities are referring to the Diamond Pattern
of the Tektronix
WFM601 as a Pass/No-Pass test for legality.  I personally
disagree and will
contest this as a valid reason for accepting or rejecting a
tape.  The Diamond
Pattern is used to determine Gamut Limits NOT Transmission
Legality.  Our in
house legal test here at Manhattan Transfer has to do with
the permissible
levels for transmission over the air on normal analog
broadcast transmitters.
We don't use either RGB (Diamond Pattern) or D-1 (CCIR 601)
"Legal" signal
levels although these are important also.  We feel here at
MTE that something
is "ILLEGAL" if it can cause a television broadcast
transmitter to
overmodulate. This can produce harmonics which will spill
over into adjacent
channels. Also, the signal should not cause the transmitter
to got to ZERO
modulation and Shut Down the carrier (Video Level too High).
 With those
criteria in mind we use the test of not creating any signal
that will have to
be limited at the transmitter to make it "Legal for
Transmission".  Clipping
or limiting the signal by the broadcaster will change the
look of the program
material that was so carefully created in the telecine,
edit, or graphics
suite.  For Commercial and Long Form clients this is not
acceptable so we
prelimit the signal at our facility in the D-1 domain.  That
way any esthetic
decisions are made with the gamut limits already built in
and the client will
not have any big surprises when he/she sees his/her product
over the air. 
But, using the Diamond Display will not limit the signal to
a "Legal for
Transmission" condition.  With 100% saturated color bars the
Diamond Display
will be quite happy  but the transmitter will not.  Clipping
of an unlimited
100% color bars signal to make it "Legal" will severely
change the look of
that signal.

We have had tapes rejected by other facilities because their
tests for
legality are different than ours.  As far as I know there is
no industry wide
standard.  I think it's time we worked on this.  What do all
of you think on
this one?

Dave Corbitt     <dc at mte.com>
Manhattan Transfer / Edit, Inc.
545 Fifth Ave.
New York, NY 10017
(212) 907-1218

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Date: Mon, 20 May 1996 10:52:01 -0400
From:  "Dave Corbitt" <dc at mte.com>
To:  "telecine group" <telecine at xyzoom.alegria.com>,
	"Bill Topazio" <bt at mte.com>, "Brian Doros"
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Subject:  [TIG] What is Legal?