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From: msc@qubix.UUCP (Mark Callow)
Newsgroups: net.video
Subject: Re: Interpreting SONY's SL2710 Manual
Message-ID: <1421@qubix.UUCP>
Date: Wed, 10-Oct-84 14:21:06 EDT
Article-I.D.: qubix.1421
Posted: Wed Oct 10 14:21:06 1984
Date-Received: Sat, 13-Oct-84 03:19:06 EDT
References: <3788@tektronix.UUCP> <217@wjvax.UUCP>
Organization: Qubix Graphic Systems, San Jose, CA
Lines: 20

> Multiplex stereo broadcasts (FM or TV) are (or will be) identified to your 
> receiver by an 18KHz pilot tone (at least for FM broadcasts. I haven't heard
> any specs for stereo TV). The presence of this carrier notifies the
> receiver that a > stereo signal is present.  The audio bandwidth of the
> signal stops at 15Khz.
> The multiplex filter takes out the carrier signal. The reason for this is
> that if you are making a recording of the broadcast, the presence of the
> tone can fool an automatic volume control, or noise reduction circuitry
> (Dolby and Dbx get hopelessly confused if the MPX tone is present.)
> 
The pilot tone is 19kHz.  It is far more than an indication to your
receiver that it is receiving a stereo signal.  It controls the PLL
(phase--lock loop) used to demultiplex the two frequency multiplexed
channels. (l+r and l-r).
-- 
From the TARDIS of Mark Callow
msc@qubix.UUCP,  qubix!msc@decwrl.ARPA
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"Nothing shocks me.  I'm an Engineer."