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Path: utzoo!watmath!clyde!cbosgd!ihnp4!qantel!lll-crg!seismo!uwvax!astroatc!nicmad!brown
From: brown@nicmad.UUCP
Newsgroups: net.video
Subject: Re: Laserdisc vs CD sound
Message-ID: <446@nicmad.UUCP>
Date: Thu, 28-Nov-85 01:30:49 EST
Article-I.D.: nicmad.446
Posted: Thu Nov 28 01:30:49 1985
Date-Received: Sat, 30-Nov-85 00:44:15 EST
References: <2266@amdahl.UUCP>
Reply-To: brown@nicmad.UUCP (Mr. Video)
Organization: Nicolet Instrument Corp. Madison WI
Lines: 63

In article <2266@amdahl.UUCP> nzm10@amdahl.UUCP (Neal Macklin) writes:
>Can someone tell me the difference between a CD, which is "digital"
>information recorded as tiny pits and reconstructed by my player into an
>analog signal, and the soundtrack (and picture for that matter) of a
>standard type (non-digital soundtrack) laserdisk, which is also recorded
>in little (on-off) pits, but which is not considered digital?  I thought
>I understood this, but I guess not...

I am sure I will be corrected on this, but it narrows down to the audio
track(s) being FM carriers.  I wish I had a book on video laser operations.
I believe that the whole video/audio bandwidth is encoded, like you say,
with pulse code modulation.  This does not have any error detection or 
correction.

>What advantage, if any, does the "digital" method on the CD have?

The advantage is that when the audio is converted to pure 16 bit digital
information, it can be played with, in order to have great (well good)
error detection and correction.

>Is there any greater immunity from noise or dirt on the playing surface
>with the digital approach?

By itself, no.  What CD technology does, is make a copy of the information
and scramble it around, so that no one length in time is one contiguous
piece.  When a glitch is found on the surface, that big hole translates
into smaller holes, which are easier to error detect and correct.  There
is more to this.  It was all explained in 'Computers & Electronics' a
while ago.  E-mail me for complete details.

>Does the analog approach offer more recording time?

Can't say, as the two formats are on different media sizes.  Plus, CDs only
have audio information on it, which is lower in bandwidth than the video and
audio on the laser disk.

>Does all this have something to do with error correction?

Don't know.

>Can't a videodisc have the same kind of interpolative error correction?

Probably not.  Since the CD error correction scheme uses copies of the
original data, there isn't enough room on the laser disk to do that.
I would suspect that an hour would become 30 minutes.

>I don't think Mr. Video has a laserdisc, so I'm depending on the rest
>of you!

No, I don't, but I couldn't pass up your edging me on, for at least some kind
of answer.

BTW, I'm sure that you have discovered by now that the video laser disk camp
now has stereo digital audio.  Where they put the information in the
available bandwidth is not known to me.  I really haven't dug into video
laser disk technology.  I probably should.
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