You may be a geek if.

From: nemo_at_net.house.cx <(nemo_at_net.house.cx)>
Date: Wed Feb 21 02:19:03 2001

On Tue, Feb 20, 2001 at 11:25:41PM -0800, Gene Buckle wrote:
> >
> > I actually worked out the approximate holding capacity of an LP once - I think
> > I assumed digital->audo modulation to be v.34 or v.42 - something like that.
>
> ...so what's the capacity? :)

Oh, I forgot to mention I'd forgotten that I have no modern idea? :)

OK, let's work this through, and forgive me any bad assumptions, incorrect
foundation information, or faulty analysis ;)

Because vinyls are fundamentally an audio media[1], we need an
audio->digital conversion system. To use modems as a base - v.42
I think is the 33.6k standard?33600bps = 4.2KB/s. This works out to
252KB/minute. What is the audio length of a vinyl? I'm not sure, but if
we make a nice round 60 minute, then we're looking at about 15meg.

Now, that's not the end of the story. v.42 is designed for modems -
duplex. LProms would be a read-only system. Also, the figure of 33300bps
is based on a modem audio resolution of 2400baud. I don't know the audio
resolution of an LP, but if I had to guess, I'd put the figure as higher
than 2400. So we're increasing capacity already. In a similar vein,
you could run the LP at 15rpm, rather than the normal 33rpm, to reduce
the resolution, while increasing the length. I'm sure there would be an
ideal somewhere between those two tradeoffs :)

Next up, we look at the modulation/demodulation to use. We'll want a
compression that takes best advantage of the medium. (I suspect v.42 is
not it!). Lastly, LP's are stereo - so that either immediately doubles
our capacity (assuming L and R can be kept 100% independant. If they can't
be guaranteed to be kept seperate, then I'm sure capacity could still be
increased by using L and R as checksums against each other or something ;)

Problems with LProms are quality of reading - you run a very real risk
of bitrot if your needle is of poor quality. Also, you'll need some
way to sync the end of sideA with the start of sideB - there is some
data loss there. (this could probably be kept to a minimum by using the
leadin/leadout areas :)

So, did I have an answer in all that? I'm pretty sure you'd get 15meg on
a vinyl easily, and could quadruple that figure with a bit of effort :)

.../Nemo

[1] If digital data can be recorded directly to vinyl, and more importantly,
read from the vinyl, then this entire analysis is meaningless :)
Received on Wed Feb 21 2001 - 02:19:03 GMT