nzm10@amdahl.UUCP (Neal Macklin) (11/27/85)
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 think it has something to do with "pulse amplitude modulation" (on the
laserdisc), but isn't that digital?
What advantage, if any, does the "digital" method on the CD have?
Is there any greater immunity from noise or dirt on the playing surface
with the digital approach?
Does the analog approach offer more recording time?
Does all this have something to do with error correction?
Can't a videodisc have the same kind of interpolative error correction?
Please answer on net or by mail. I'll summarize to the net any replies
I get by mail, if people want me to.
I don't think Mr. Video has a laserdisc, so I'm depending on the rest
of you!
--
Neal Macklin
(408) 737-5214
...{hplabs,ihnp4}!amdahl!nzm10
[There are no opinions expressed in this article].brown@nicmad.UUCP (11/28/85)
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. -- ihnp4------\ harvard-\ \ Mr. Video seismo!uwvax!nicmad!brown topaz-/ / decvax------/
caf@omen.UUCP (Chuck Forsberg WA7KGX) (11/30/85)
In article <446@nicmad.UUCP> brown@nicmad.UUCP (Mr. Video) writes: >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. LV Digital Audio information is stored in the 0 to 2 mHz band, same coding as Compact Discs. The analog soundtracks are at 2.3 and 2.8 mHz (FM, 75 us preemphasis, 100 kHz modulation). The FM soundtracks are often CX encoded to yield a total of 70+ db s/n ratio. The video is directly modulated on an 8 mHz carrier, with a bandwith better than 4 mHz, about twice as good as VHS or Beta. The analog sound tracks give as good sound as VHS or Beta Hi-Fi, but without head switching noise. The actual quality difference on movies tends to be more pronounced because tape duplication involves more generations. -- Chuck Forsberg WA7KGX ...!tektronix!reed!omen!caf CIS:70715,131 Omen Technology Inc 17505-V NW Sauvie Island Road Portland OR 97231 Home of Professional-YAM, the most powerful COMM program for the IBM PC Voice: 503-621-3406 Modem: 503-621-3746 (Hit CR's for speed detect) omen Any ACU 1200 1-503-621-3746 se:--se: link ord: Giznoid in:--in: uucp