Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!ucsd!sdcsvax!ucsdhub!hp-sdd!robert
From: robert@hp-sdd.hp.com (Robert Navarro)
Newsgroups: sci.electronics
Subject: Re: Stereo vs. Mono: Q about AM Stereo
Keywords: AM,radio,stereo,mono,FCC
Message-ID: <1968@hp-sdd.hp.com>
Date: 2 May 89 20:41:09 GMT
References: <4046@bgsuvax.UUCP>
Sender: news@hp-sdd.hp.com
Reply-To: robert@hp-sdd.hp.com.UUCP (Robert Navarro)
Organization: Hewlett-Packard, San Diego Division
Lines: 48

In article <4046@bgsuvax.UUCP> klopfens@bgsuvax.UUCP (Bruce Klopfenstein) writes:
>
>
>He wants "proof" that stereo is superior to mono.  You can laugh, but I have
>to answer this person's criticism.  While I stated in the article that stereo
>gives sound presence and thought it went without saying that stereo is superior
>to mono, the reviewer wants more.
>
>I need help explaining why AM stereo is superior to AM mono (yes, I know AM
>stereo limits the distant AM signal, but my argument is that AM stereo at the
>very least couldn't hurt AM efforts to win back some audience).
>

   I'm not laughing at the person who asked for proof that stereo is better
than mono because in one important way it's NOT. The signal to noise
ratio for Stereo is lower than mono. This means the signal sounds more
noisy for stereo. To see this just tune your FM radio to a station that
barely comes in in stereo and then turn the stereo off. (This is why
most FM receivers have the mono switch ! -- to allow weak stations to
be better received.)

   Furthermore, AM is badly bandlimited. The baseband signal for AM is only
5KHZ! Most music requires at least twice this for decent sound 
reproduction. To include stereo into AM would require more bandwidth.
And, unless you use single side band (which usually adds some noise 
in practice) the 5Khz for the baseband signal now must be divided
up into two channels for stereo. Can you imagine what a 2.5Khz bandlimited
signal would sound like!!!!

So, while stereo AM may sound more like an original stereo music 
recording, it will also sound noticably noisier than mono 
no matter what AM stereo standard is picked. 

By the way, FM is better not because it is in the higher frequency
ranges, but because FM is inherently a less noisy modulation
scheme for radio frequencies than AM. FM does take up more bandwidth
than AM but at the higher frequencies that bandwidth is 
availiable. So FM trades off greater bandwidth for less noise. 
Because of this inherent superiority, AM really doesn't stand a chance
in terms of high quality (noiseless) reception.

-----------------------------------------------------------------
Robert Navarro
Hewlett Packard, San Diego


-- 
Robert Navarro