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From: john@tower.UUCP (John Moore)
Newsgroups: sci.electronics
Subject: Re: FM audio recording?
Message-ID: <91@tower.UUCP>
Date: Fri, 25-Sep-87 10:29:58 EDT
Article-I.D.: tower.91
Posted: Fri Sep 25 10:29:58 1987
Date-Received: Sun, 27-Sep-87 02:00:03 EDT
References: <3746d52b.b8ab@apollo.uucp> <231@piglet.UUCP> <1574@dicome.UUCP> <235@piglet.UUCP> <1588@dicome.UUCP>
Reply-To: john@tower.UUCP (John Moore)
Organization: Anasazi Inc, Phoenix AZ
Lines: 43

In article <1588@dicome.UUCP> plate@dicome.UUCP (Douglas B. Plate) writes:
>Newsgroups: sci.electronics
>Subject: Re: FM audio recording?
>Summary: 
>Expires: 
>References: <3746d52b.b8ab@apollo.uucp> <231@piglet.UUCP> <1574@dicome.UUCP> <235@piglet.UUCP>
>Sender: 
>Reply-To: plate@dicome.UUCP (Douglas B. Plate)
>Followup-To: 
>Distribution: 
>Organization: DICOMED Corp., Minneapolis
>Keywords: 
>
>In article <235@piglet.UUCP> sjb@piglet.UUCP (Seth J. Bradley) writes:
>)In article <1574@dicome.UUCP), plate@dicome.UUCP (Douglas B. Plate) writes:
>)) In article <231@piglet.UUCP> sjb@piglet.UUCP (Seth J. Bradley) writes:
>)) )ungodly bandwidth FM requires.  15KHz stereo broadcasts use about

Since the discussion is on bandwidth, let me point out that FM bandwidth
(especially wideband FM  such as commercial broadcasting) is not simply
the sum of the audio frequencies present, or even just the highest
frequency present. Rather, it is a complex set of bessel functions.
For a single tone, one gets an infinite series of sideband terms, the
amplitude of the Nth sideband equal to the Nth bessel function of
a relationship between the peak frequency deviation and the frequency
of the tone (sorry I'm being vague, but in a hurry and don't have time
to look up the exact formula).  For more than one tone, one gets multiple
series based on cross products of all the components, yielding a large
number of sidebands (more than you would expect from any linear analysis).
Thus, the "bandwidth" is infinite, but for practical reasons the
bandwidth is defined by when the sidebands drop below a certain level
relative to the carrier.
	Now, you might ask, why the 200Khz deviation? Well, it turns out
that in a noisy environment, the recovered signal is less noisy for
wider bandwidths. FM could have used a smaller bandwidth, and transmit
the data with the same fidelity, with the exception of signal-to-noise
ration.
	For further reference on this, look at the Radio Engineers
Handbook.

	John Moore
	Anasazi, Inc
	Somewhere in Phoenix, AZ