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From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Fiber Optic Sound Cables ...
Keywords: NeXT, CD (music) Player.
Message-ID: <8979@milton.u.washington.edu>
Date: 11 Oct 90 02:52:04 GMT
References: <4218@rsiatl.UUCP> <20293@ucsd.Edu> <314@foxtail.UUCP>
Organization: University of Washington, Seattle
Lines: 23

In article <314@foxtail.UUCP> kravitz@foxtail.UUCP (Jody Kravitz) writes:
>>mackenzi@Apple.COM (Steven MacKenzie) writes:
>>>>My question is ... why would any one want to use fiber optic to transmit
>>>>digital data 6 feet or so?
>
>The issue here it so keep the (unconverted) digital signal out of the
>audio.  The clock rate in the cable is 44,100 * 2 * (16 bits + framing). Thats
>about 1.5MHz.  Fast rise times and TTL signal levels would invite coupling...

	Actually, the fast-rise signals are created deliberately, at each
end of the transfer, anyway.  And, the straight 'eye pattern' off
the photodiode detector is bandwidth limited, so would be trivial to
buffer and send (through a transformer if you want to keep current
loops out of the picture) to any other box.  Additionally, optical links
don't develop good bandwidth on short cables (oddly, the attenuation
in the cable is necessary to keep high-frequency 'ringing' from 
occurring in the fiber link); in short, the optical link has NO 
advantage over simple balun/twisted pair wiring.
	The decision, IMHO, was simple gee-whiz marketing.  Someone
said to a group of engineers, 'What can we offer the customers, that
our competition will take months or longer to match?'

I am known for my brilliance,                  John Whitmore
 by those who do not know me well.