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From: jeh@ritcv.UUCP (Jim Heliotis)
Newsgroups: net.video
Subject: Re: Stereo vs. Hi-Fi\
Message-ID: <1498@ritcv.UUCP>
Date: Mon, 28-Jan-85 15:11:54 EST
Article-I.D.: ritcv.1498
Posted: Mon Jan 28 15:11:54 1985
Date-Received: Fri, 1-Feb-85 01:05:50 EST
References: <266@decwrl.UUCP> <7751@brl-tgr.ARPA>
Organization: Rochester Institute of Technology, Rochester, NY
Lines: 46

> VHS doesn't encode the HI-FI on the video head.  If this is true that
> explains why Sony kept claiming it would be impossible for VHS to do
> HI-FI without degrading the video.  Anybody know for sure?
> 
> -Ron

Many people who do know for sure have already explained this, but perhaps
not in a clear enough way, so I'll make a stab at it.

The Meaning of "HEAD":  This has two popular meanings.  The 'real' one is
each of the set of little things spinning around in your VCR, or the things
you have in any tape recorder for audio.  This is what is being referred to
when salesmen brag about 3-, 4-, or 6-head VCR's.  The other popular use is to
use "head" to mean the spinning metal cylinder, the drum, which holds all the
video (and VHS HiFi, see below) heads.

In all video tape recorders, the video information components are modulated
at various frequency bands and sent out to the video heads for recording.
The bands chosen for Beta are more spread out than those chosen for VHS.
Therefore, when SONY decided to build in HiFi sound, all it did was use
one of the "spaces" between the video bands and use it to modulate the
2 audio channels. Therefore, to play the audio, you just use the video
heads, and then employ circuitry to separate/filter out the audio bands.

SONY said that VHS could not do this, due to lack of space between video
bands, (they could if they narrowed the video bandwidth, causing picture
degradation, in order to create spaces for audio) and they are right.
So instead, VHS decided to first record the HiFi audio information on the
tape, using frequencies which conflict with the video signals, but write to
the tape "at a different angle" (that's as technical as I feel it's safe for
me to get). Then, the video is written "on top of" the audio signals.  It turns
out that it is possible to extract both types of information off the tape if
/different\ heads are used to read the information at the same angles at which
they were written.

Thus we have a situation where extra audio heads are placed on the video
drum to make VHS HiFi.  So, an n-head Beta HiFi machine is potentially
equivalent to an (n+2)-head VHS HiFi machine, and I wonder how many people
know that.

Hope this makes things clearer, without my being wrong!

				Jim Heliotis
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