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From: ron@brl-tgr.ARPA (Ron Natalie )
Newsgroups: net.audio
Subject: Re: Copy protected records?
Message-ID: <8221@brl-tgr.ARPA>
Date: Sun, 10-Feb-85 23:00:15 EST
Article-I.D.: brl-tgr.8221
Posted: Sun Feb 10 23:00:15 1985
Date-Received: Wed, 13-Feb-85 02:47:43 EST
References: <305@boulder.UUCP>
Distribution: net
Organization: Ballistic Research Lab
Lines: 17

> 
> 	I have heard rumors from a couple of sources now that some record
> companies are adding a high frequency signal to their records that 
> interfere with the bias on tape decks, thus making it difficult to make
> tapes of said records.  Does anybody know if this is really true, and
> if so, just what the technique is?
> 
'Twould seem to me that any signal high enough to be inaudible and also
interfere with my tape deck bias would also be severely diminished by
the fact that my stereo rolls off the high end very quickly above what
I find to be inaudible (which is higher than most people).  Since they
are obviously targeting this at cassettes, all you'd have to do is zap
your equalizer to not try to record above the top level that cassettes
are capable of recording.

The only thing I could think of is that they are beating the bias
frequency down to something audible to ruin the recording.