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From: perkins@bnrmtv.UUCP (Henry Perkins)
Newsgroups: net.video,sci.electronics
Subject: Re: Number of VCR heads
Message-ID: <819@bnrmtv.UUCP>
Date: Tue, 28-Oct-86 02:13:06 EST
Article-I.D.: bnrmtv.819
Posted: Tue Oct 28 02:13:06 1986
Date-Received: Wed, 29-Oct-86 09:07:57 EST
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> I am trying to get TRUE and COMPLETE information on function of
> number of video heads in a VCR.
> Michael Umansky (misha)

Video magazine has an article about video heads roughly once a year.
There are several different head designs, but here's the basic story
for VHS.

The minimum number of heads necessary for a VCR is two.  Each head
does one half frame, and the heads are 180 degrees apart on the head
cylinder.  However, a given head width can only be optimized for one
speed of play.  Cheap machines will perform well at only one speed
(often EP), with adjacent tracks bleeding at a slower speed, and
inter-track noise showing up at a higher speed.  That's why all the
machines with decent performance at more than one speed have a second
pair of heads.  Then you have one pair for SP and one pair for EP.

Frequently a single extra head is added to better support special
effects like freeze frame and slow motion.  This gives 3 heads on the
cheap machines, and 5 on the better ones.

Things get more complicated from there.  In some machines LP is done
by combining one SP head with one EP head.  Many otherwise good
machines don't even allow recording at LP speed.  As far as I know no
manufacturer has three separate pairs of video heads to support the
three recording speeds.

For HiFi, where the two audio tracks are laid down "under" the video
tracks, add two more heads.  That's how you can get 6 or 7 heads.
More properly, these are 4+2 or 5+2 heads, since you don't get any
better picture by adding the HiFi heads. (Normal linear audio is
recorded on the edge of the tape by a single non-moving head.)


Beta is much simpler.  You still have two opposed heads to record
the picture.  However, the tolerances are not as restrictive, so
you can handle both Beta II and III speeds with the same pair of
heads.

Beta HiFi records the two audio tracks with the video signal, not
"under" it.  You need more circuitry, but you use the same two heads.

Except for the very-top-of-the-line-with-all-the-editing-effects
models, SuperBeta HiFi machines still only have two heads.  The
fanciest machines (like my Sony SL-HF900 SuperBeta) have 4 heads.


A two-head SuperBeta VCR (costing about $350) has 20% more resolution
than a 5+2 head $1400 VHS HQ machine.  It's a shame Sony can't market
their products as well as JVC.
-- 
{hplabs,amdahl,3comvax}!bnrmtv!perkins        --Henry Perkins

It is better never to have been born.  But who among us has such luck?
One in a million, perhaps.