Why can't CD's be analogue?

[Hawklord]

What got me wondering was while I was watching a LD the other day. The picture on LD's is anlogue on an optical disc. So why can't music be put to disc as an analogue signal?

[lil.fred]

It can, as you surmise. As with LaserDisc, though, the amount of information to be encoded would call for a physically quite large object. But no larger than a LD.

The movies originally recorded sound (before magnetic tape) optically -- sound waves were used to modulate a visual signal which was then read optically by the projector.

[Hawklord]

OK so we would need a larger disc. Well I guess that aint gonna happen. I just thought that it seems that even in the digital relm we seem to be striving for that analogue sound/feel.

[JoelDF]

Don' t forget that the early LD standard called for 2-channel analog sound too. Later it included a 2-channel PCM (digital) track, but retained the analog tracks for compatibility with older players (until Dolby Digital AC-3 came along and took up the right analog channel's space). The dynamic range was fairly high if I recall and considered to be of very high quality (once CX noise reduction was added). The quality of the analog tracks is one of the reasons DTS decided to take over the PCM track space and leave both analog tracks intact for their Laserdisc releases.

CLV LD is 60 minutes long per side, but that includes the picture and the sound - the picture takes up much more of the bandwidth. Yet there was still enough bandwidth available to later include the digital tracks - and we know how much space 2-channel PCM takes up if 74 minutes fits on CD.

Although isn't LD PCM sampling at 48kHz? Can't remember.

It seems that analog sound read by laser could be done on a smaller than 12" disc.

Anyway, maybe the smaller blue laser wavelength could help if someone were to try this.

Oh, and then there is the Laser Turntable (http://www.elpj.com/frameset.html). :)

Joel

[Ken_McAlinden]

Laserdisc analog sound was RF encoded. CX noise reduction was not without its own problems. DTS took up the digital tracks because they were 44.1KHz 16 bit PCM just like CDs, so the bandwidth and ability to pass it through a digital output were identical. It had nothing to do with the quality of the analog tracks, not that I'm saying they were bad.

It is probably not beyond the pale to produce a 5" analog optical disc, but that ship appears to have sailed long ago.

Regards,

[sgraham]

You all are right, an audio-only analog optical disk could certainly be made, and there's no reason why the sound quality couldn't be very good. If there was no video to take up all the bandwidth, you could use straight FM with no CX, and very wide carrier deviation for wide-range, low-distortion audio. I'd love to hear such a device, I'll bet it'd be spectacular. But as Ken said, that ship has probably sailed. Record companies would hate it because it wouldn't be digital, hence you couldn't make perfect, bit-for-bit copies... er, wait a minute!....

[RetroSmith]

Well, nobodys "going back to analog". Its a nice idea, but wont fly. I think that would be percieved by the public as going backwards, leading to poor sales. The buzzword today is of course, digital.

[EC3970]

today maybe, but weren't digital watches all the rage once? Not a good comparison, I know, but analog may be back. The concept has a strong connection to quality.

[Michael]

Yea, Those Big Black 12" things called reords...Digital is here to stay, leave the analog where it belongs on those Big Black 12" Long Playing Records...

[Grant]

You can't make a CD work like analog. It's an almost physical impossibility.

[lukpac]

Originally posted by Grant
You can't make a CD work like analog. It's an almost physical impossibility.

Why do you say that, Grant? How would such a thing be very different from Laserdisc?

[Grant]

Originally posted by lukpac


Why do you say that, Grant? How would such a thing be very different from Laserdisc?

Size.

[tone ded freb]

Size matters?:)

[lukpac]

Originally posted by Grant
Size.

What about size? One of the reasons Laserdiscs are so big is because they hold *video*. An audio-only medium wouldn't.

Not to mention the fact that newer types techniques can fit more data onto a disc.

[-=Rudy=-]

I've had four LD players and never was impressed with the analog vs. the digital channels. To me they were always dull sounding, a bit muffled, not as detailed. On some LDs they're very close, but on some others, the difference is quite noticeable.

I never bothered with worrying about AC3 vs. DTS in LDs either. I wasn't equipped to decode them, and didn't want to have to get two decoders to sort it out. It isn't as much an issue now that DVD is so readily available. :)

[Ken_McAlinden]

Originally posted by Rudy@A&MCorner
I've had four LD players and never was impressed with the analog vs. the digital channels. To me they were always dull sounding, a bit muffled, not as detailed. On some LDs they're very close, but on some others, the difference is quite noticeable.

I never bothered with worrying about AC3 vs. DTS in LDs either. I wasn't equipped to decode them, and didn't want to have to get two decoders to sort it out. It isn't as much an issue now that DVD is so readily available. :)
Rudy,
If the analog audio did not have to be encoded into such a relatively small bandwidth, it could sound better. Presumably, with an audio only format and no video to worry about, they could come up with an optical analog 5" disc that sounds better than the RF analog outputs from a laserdisc.

Of course, this isn't going to happen, but it can be fun to dicscuss. :)

As an aside, and not that it's the best hi-fi example, but optical analog film soundtracks have been with us for decades (on film, not just aluminum discs).

Regards,

[Michael St. Clair]

I've heard some LDs where the CX analog audio was very nice and clean sounding. Warm too!

I've also heard a bunch that were just awful.

I'd imagine a lot of care wasn't taken on many discs once the digital LD audio format was standardized.

The player probably makes a difference also.

[Paul C.]

With the high data density of DVD-generation discs (eg. SACD, DVD-A, DVD-V etc), surely disc size would not be a problem. I still don't understand how you store analog on a digital disc.

[Grant]

Originally posted by Paul Christie
I still don't understand how you store analog on a digital disc.

Exactly! Or, why one would want to.

[-=Rudy=-]

Originally posted by Ken_McAlinden

As an aside, and not that it's the best hi-fi example, but optical analog film soundtracks have been with us for decades (on film, not just aluminum discs).


There were actually some albums in the 60's that were mastered this way, onto 35mm film. The only one I own that I know is mastered this way was Esquivel's More of Other Worlds, Other Sounds, which came out on Reprise (due to RCA not wanting to release it...so we know the mastering wasn't done at RCA). The CD sounds pretty much normal, but a bit shy on the ultra-high frequencies.

I'd be interested to hear if Steve has had any experience with these masters, or which studios or record companies tried it.

[lukpac]

Originally posted by Paul Christie
I still don't understand how you store analog on a digital disc.
Originally posted by Grant
Exactly! Or, why one would want to.

As far as "how", well, it's not a digital disc, of course! As has been previously mentioned, Laserdiscs have had *analog* soundtracks for years.

As for "why", well...the same reason people continue to listen to LPs, I guess. Because they feel that analog offers something that digital doesn't. I'm not saying I necessarily *agree* with that viewpoint, but...

[lucifer-chops]

Originally posted by lukpac


As far as "how", well, it's not a digital disc, of course! As has been previously mentioned, Laserdiscs have had *analog* soundtracks for years.


When you say it's not a digital disc do you mean that the information is not stored in the form of pits on the surface on the disc that will either reflect the laser or not? If the information is not stored in this way then how can it be stored?

[Michael St. Clair]

When you say it's not a digital disc do you mean that the information is not stored in the form of pits on the surface on the disc that will either reflect the laser or not? If the information is not stored in this way then how can it be stored?


Oh, it uses pits all right. But instead of uniform pits for ones and zeros, it uses different lengths of pits with different spacing, this information is used to modulate sets of analog signals for video and audio.

Optical does not mean digital.

[JoelDF]

Originally posted by Michael St. Clair
Oh, it uses pits all right. But instead of uniform pits for ones and zeros, it uses different lengths of pits with different spacing, this information is used to modulate sets of analog signals for video and audio.

Optical does not mean digital.
It's called PFM - Pulse Frequency Modulation. And, in our postulation (if that's a word), we are only considering the audio.

Joel

[Mal]

Originally posted by Michael St. Clair


Oh, it uses pits all right. But instead of uniform pits for ones and zeros, it uses different lengths of pits with different spacing, this information is used to modulate sets of analog signals for video and audio.


To be clear, the digital storage system utilised in optical disc technonlogy uses pits and lands of different lengths - not uniform ones. The transition from pit to land (and vice versa) represents a "1" while the length of pit or land between the transitions dictates the number of "0"s between the "1"s.

:cool: