From: brown@vidiot.UUCP (Vidiot)
Newsgroups: rec.video
Subject: Re: HiFi vs Dolby Stereo
Date: 27 Sep 92 09:59:44 GMT
Reply-To: brown@vidiot.UUCP (Vidiot)
Organization: Vidiot's Hangout

In article <1992Sep26.191312.11837@ccu.umanitoba.ca> umcarls9@ccu.umanitoba.ca (Charles Carlson) writes:
<In <1686DA936.M02449@mwvm.mitre.org> M02449@mwvm.mitre.org (Joe Gems) writes:
<
<>Stereo (non HiFi) VCRs lay down two very skinny linear audio tracks at one end
<>of the tape width (using the same width of tape as mono VCRs use for their one
<>audio track). 
<
<[...]
<
<>Hi-Fi VCRs use an entirely different recording technique, whereby the audio
<>information uses the full tape width (i.e., the audio and video information
<>are both recorded in the same tape space, but are multiplexed so as to be
<>separately decodable). HiFi VCRs have audio specs comparable to DAT, which is
<>a far cry from standard audio tape.
<
<This doesn't make any sense to me.  
<
<If the stereo VCR uses two skinny audio tracks in the same place as a
<mono VCR uses its one, then how does a stereo VCR reproduce the sound
<a mono VCR makes and vice versa?

Does this mean you don't know how an audio cassette works either?  The principle
of linear stereo VCRs is exactly the same as audio cassettes...

Take a small portion of the video tape, in this case the top edge of the video
tape.  The audio width for VHS tapes is 1.0 mm.  That is the width for the mono
track.  Now, take that width and cut it into three pieces.  The piece nearest
the edge is the right channel and it is .35 mm wide.  Move down the tape to
the next piece, which is a guard band and it is .3 mm.  Move down even further
and you get to the last piece, which is the left channel and it is .35 mm
wide.

<Also, if the Hi-Fi VCRs use the tape for audio as you described above, then
<how does my old RCA Dolby stereo VCR pick up the stereo effects of Hi-Fi
<tapes? (Unless commercial tapes are recorded in both Hi-Fi and stereo?)
<I know I have heard stereo effects on my RCA such as in a movie when a 
<car goes past, it will fade in one side, and out the other.

No, Hi-Fi VCRs have two places where audio is recorded: the old method using
the linear head and a new method using the video drum.  Two FM carriers are
placed on the tape using separate heads on the video drum.

Prerecorded movies are recorded in Hi-Fi stereo as well as linear stereo with
Bolby B noise reduction.

<I also have a Sony SLV-595HF Hi-Fi VHS.  I was hoping to do some dubbing
<of Hi-Fi tapes such as playing them on the RCA and recording them on the
<Sony.  I realize I will loose quite a lot of sound quality, but I was
<hoping I would atleast maintain the stereo effects, but from my interpretation
<of your above explanation, it doesn't look like I'm going to be able to.

Yes, you'll be able to get stereo sound and you are correct in that the audio
quality will be poor.  But, if you are copying prerecorded tapes, the chances
are you won't be able to record them anyway, because of Macrovision.
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