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From: ltran@pluton.matrox.com (Linh TRAN)
Newsgroups: comp.sys.amiga.multimedia
Subject: Re: Toaster Output?
Message-ID: <1991Feb1.194032.8028@pandora.matrox.com>
Date: 1 Feb 91 19:40:32 GMT
References: <189a59cc.ARN0dfb@cbmami.UUCP>
Sender: news@pandora.matrox.com (Usenet Administration)
Organization: Matrox Ltd.
Lines: 63

jason@cbmami.UUCP (Jason Goldberg) writes:


>	I am doing some work with a local community colleges Television and
>Radio department.  The chair of the department says that they can afford to
>purchase (and would very much love the capabilities) a few video toaster w/
>Amigas.  The problem is that their engineer doesn't feel that the toaster
>provided "NTSC quality output."  Now I am under the impression that
>broadcast quality is a mythical term, and that NTSC quality would be
>anything which could be displayed with NTSC equipment, which obviously the
>toaster can.
>	The real point here, is that the engineer doesn't feel that the
>toaster has good enough quality output for him.

	I saw that the Video Toaster has problem with unstable source such
as normal VCR. May be that is why the engineer said that it does not have
Broadcast Quality. 

	Given that Quality, Broadcast or not, is somewhat an arbitrary 
entity, depending on your applications.

	If you use VCR as one source of input, then I suggest you to check
the output when it display what come from the VCR. You could then judge
by yourself if the output is Broadcast Quality or not, and if it suit
your purpose. You then could make the trade-off between the price of the
VCR and your other video equipement. Remember that video equipements must
work well together and the price is the price of the whole system.

	Inexpensive VCR have jitter because the syncs are stored as is
on the tape. At record time or playback, the video sync frequency could
change a bit. This is because the servo mechanism  and the strectching
of the tape. Expensive VCR has its own jitter compensation (or time base
correction on the high end).

	Camera works fine because the output is stable (the whole camera
circuitry depends on crystal frequency).

	The Video Toaster, after what I have heard, sample the video
(composite) directly. It seems not to have the ability to resynchronize
with the burst signal, making phase discrepencies accumulated. NTSC 
signal is not robust for phase discrepencies (hue error). That is why
the sample frequency of frame-grabbers are multiple of burst frequency
(for NTSC: 4 times ~ 3.5MHz).

	Now, if the sampling frequency is fixed, and the line is abit
shorter or longer than the standard line, the sampling points for the
I and Q component is no logner in phase with the NTSC burst, making
a degraded color output. 

	Finally, although I am pretty sure of what I am talking about,
I am not trying to discredit NetWorx (Video Toaster's maker). Maybe
the engineers from NetWorx could confirm or explain if the above
speculations are well found or not.

Linh Tran.
        
	This is my opinion. This has nothing to do with my employer.
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