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From: bobr@zeus.UUCP (Robert Reed)
Newsgroups: net.video
Subject: Re: Using Hi-Fi VCRs for Audio Recordings
Message-ID: <402@zeus.UUCP>
Date: Mon, 29-Oct-84 04:11:21 EST
Article-I.D.: zeus.402
Posted: Mon Oct 29 04:11:21 1984
Date-Received: Thu, 1-Nov-84 03:03:51 EST
References: <696@ihuxa.UUCP>
Organization: Tektronix, Beaverton OR
Lines: 34
Cc: allegra!ihuxa!pnovak

I just saw something in the Oct 15 ElectronicsWeek that may help answer your
questions:

    According to most experts, the audio in either VCR format sounds
    about the same; even a practiced ear would have trouble differentiating
    VHS's high fidelity from Beta's.  But they do work differently.

    In Beta Hi-Fi, the FM carrier is recorded onto the video tape
    simultaneously with the video signal, using the same set of rotating
    heads.  The VHS technique, by contrast, uses separate audio heads on the
    video head to record the stereo signal deep within the tape's magnetic
    coating.  The video signal is recorded over the audio program, close to
    the surface of the tape.  Difference azimuth angles for the audio and
    video playback head minimize cross-talk.

    The signal-to-noise ratios for both formats are low, however, and must
    therefore be compensated for with noise-reduction circuitry.  Both
    formats use proprietary encode/decode companding schemes similar to the
    Dolby and dbx systems on most home stereophonic audio systems.  To
    ensure compatibility with standard VCSs, the manufacturers of VHS and
    Beta Hi-Fi machines have made provisions to record conventional
    longitudinal soundtracks simultaneously with the FM high-fidelity
    carrier.

Thus according to this article, what makes video Hi-Fi so good is the
combination of improved tape speed (being on the video head) and standard
audio compression techniques.  I've heard people claim that dbx style
compression can give the effect of digital audio, and it appears that this
is what is happening with both VHS and Beta Hi-Fi.  CD's probably have
better specs and would certainly be better over time than video hi-fi.  Of
course, you could always buy a digital PCM converter for your video recorder
and have true digital, both recording and playback.
-- 
Robert Reed, Logic Design Systems Division, tektronix!teklds!bobr