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From: jerry@psivax.UUCP (Jerry Askew)
Newsgroups: net.video
Subject: Re: HiFi Compatibility With Dolby Stereo?
Message-ID: <632@psivax.UUCP>
Date: Wed, 7-Aug-85 20:45:03 EDT
Article-I.D.: psivax.632
Posted: Wed Aug  7 20:45:03 1985
Date-Received: Mon, 12-Aug-85 08:24:37 EDT
References: <668@ihu1g.UUCP>
Reply-To: jerry@psivax.UUCP (Jerry Askew)
Distribution: net
Organization: Pacesetter Systems Inc., Sylmar, CA
Lines: 36

First off, forgive me if the format is kind of dull because this is my
first article.

In the beginning...(of VHS tape,) the format was quite simple.  The tape
was divided into 3 sections.  Starting from the top, the first section was
allocated for audio.  The audio track is about 1mm in thickness and
contains audio information recorded in the usual format that we are all
used to (linear recording, just like cassette tape.) The second section is
dedicated to the video information (More on that later.)  The third section
is given to the control track.  This track, also 1mm wide, contains a 30hz
pulse that helps the recorder to synchronize its video heads with the video
information that is on the tape.

     Video information is laid down in the video area using a recording
technique known as helical scanning.  The video information is put on the
tape in diagonal 'tracks'.  The reason for this is that the spinning action
of the heads makes the relative head to tape speed approx 3 metres per
sec!!! this gives the necessary fidelity to reproduce a video signal whose
upper freq limiit approaches 4mhz!

	Somewhere along the line, some brilliant engineer figured that if
video could benifit from the extrordinary bandwidth & flattness of helical
recording, why couldn't audio??  Hi Fi was created.  The only problem now
is where to put the helical audio tracks.  A new recording technique was
developed...called deep layer recording.  Hi Fi audio information is
recorded UNDERNEATH the video information, therefore you have 2 independant
stereo audio 'channels' on a hifi recorder.

    The summary of the above is that hifi audio is COMPLETLY seperate from
    standard 'linear' stereo audio & should have no effect on the operation
    of a 'linear' recorder.  Most tapes that have hifi tracks on them are
    recorded in dolby stereo but this is not required.

			      Hope that my fist try helped somebody!
				      Jerry Askew
				      psivax!jerry