Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!utgpu!water!watmath!watcgl!onfcanim!dave
From: dave@onfcanim.UUCP
Newsgroups: comp.graphics
Subject: Re: Mixing computer and video signals
Message-ID: <15354@onfcanim.UUCP>
Date: Fri, 3-Jul-87 13:34:02 EDT
Article-I.D.: onfcanim.15354
Posted: Fri Jul  3 13:34:02 1987
Date-Received: Sat, 4-Jul-87 15:18:06 EDT
References: <173@mv06.ecf.toronto.edu> <3119@eagle.ukc.ac.uk> <804@puff.WISC.EDU> <15342@onfcanim.UUCP> <22455@sun.uucp>
Reply-To: dave@onfcanim.UUCP (Dave Martindale)
Organization: National Film Board / Office national du film, Montreal
Lines: 27

In article <22455@sun.uucp> cmcmanis@sun.UUCP (Chuck McManis) writes:
>
>Well in Jeff's case it *IS* true, because the Amiga generates NTSC video
>on its composite video output connector. Color subcarrier and everything.
>It is however, in the case of the Amiga, easier to sync the Amiga to 
>the studio than vice versa, you just feed in external sync to the RGB
>connector.

I stand corrected about the Amiga.

There is an additional reason to want to lock the Amiga to the studio's
sync generator rather than vice versa:  To meet NTSC specs, the
oscillator in the studio's master generator has to be extremely stable
- about 3 parts per million absolute frequency accuracy, and very low
drift rate over time.  To achieve this, either a crystal in a
temperature-regulated oven or a temperature-compensated crystal
oscillator are used.  If the Amiga is locked to the studio's generator,
the Amiga's output video will also be this stable.

If you lock the studio's generator to the Amiga's composite output,
then the studio's sync generator stability will be degraded to whatever
standard the Amiga's presumably simpler oscillator provides.  Since the
sync generator also drives any VTRs, switchers, etc.  that are in use,
the entire editing studio is now locked to the Amiga.

If you have a choice, it's best to pick the most stable sync source
available.