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From: sdyer@bbncca.ARPA (Steve Dyer)
Newsgroups: net.audio
Subject: Re: Phase Linear model 1000 questions
Message-ID: <212@bbncca.ARPA>
Date: Fri, 21-Oct-83 12:35:11 EDT
Article-I.D.: bbncca.212
Posted: Fri Oct 21 12:35:11 1983
Date-Received: Sat, 22-Oct-83 09:17:40 EDT
References: <318@psuvax.UUCP>
Organization: Bolt, Beranek and Newman, Cambridge, Ma.
Lines: 28

The Phase Linear 1000 "Auto Correlator" noise reduction unit is a one-way
device much in the spirit (if not in execution) of the Burwen Dynamic
Noise Filter and the more recent National Semi DNR chips.  Any program
material will work with it, regardless of whether it's been previously
unprocessed, or if it's been thru the two-way Dolby noise reduction.

Here's a diagram of how both work:

input signal                   encoded signal                 output signal
--------------> [DOLBY ENCODE] ---------------> [DOLBY DECODE]------------>
+ original		       on tape + tape                 less tape hiss
  noise					 hiss                 All original noise


input signal                   output signal
--------------> [PHASE 1000]   --------------->
+ noise                        + less noise


These one-way noise reduction systems are more "powerful" than Dolby, because
they do not "care" about the source of the noise--Dolby only reduces noise
added in the duplication process.  It cannot remove noise in the original
signal.  On the other hand, the Phase has to "guess" as to what is noise
and what is original signal, and this is why it doesn't always do a perfect
job.  But, with careful calibration, it works very well.

/Steve Dyer
decvax!bbncca!sdyer