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From: siri@otc.otca.oz (Siri Hewa)
Newsgroups: comp.sys.amiga.multimedia
Subject: Re: Toaster Output?
Message-ID: <2305@otc.otca.oz>
Date: 13 Feb 91 00:51:30 GMT
References: <189a59cc.ARN0dfb@cbmami.UUCP> <1991Feb1.194032.8028@pandora.matrox.com>
Reply-To: siri@otc.research.otca.oz.au (Siri Hewa)
Organization: OTC Development Unit, Australia
Lines: 51

In article <1991Feb1.194032.8028@pandora.matrox.com> ltran@pluton.matrox.com (Linh TRAN) writes:
>jason@cbmami.UUCP (Jason Goldberg) writes:
>
>>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.
>
>	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).
>
>	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. 
>
>PHU"O"NG NGUYE^N    

Re.your comment above if you use a pll with secondary lock such as vcxo,then
you should not have any hue errors.This is at front end of the video after the
sampling.
Re.output of the video,if they have stability problems then this can be cured
by redisigning the spg(sync pulse generation).But output video quality come
from video coder design.
So to the conclusion first rubbish in = rubbish out.
Assuming this is not the case,problem may be at the front end of the
video.Looking at the toasters price range they may have opt for the cheaper
decoding circuitry.
By the way Broadcast quality is well define in technical terms. Subjective
quality come from years in the field.
Iam a broadcast engineer who has design top end equipments in UK.
It will be interesting if some one get hold of Tektronic video mesurement unit
(Answer or the later one) and do real masurement on toaster.

Siri Hewa.
||||OTC||
R&D Visual Communication
siri@otc.otca.oz.au