Re: "analog computer" = useless hypothesis?

From: Jim Fehlinger (
Date: Sun Apr 01 2001 - 15:26:37 MDT

"J. R. Molloy" wrote:
> From: "Anders Sandberg" <>
> > There is currently a big debate among us neuroscience people about
> > rate coding vs. spike coding. Neurons in mammals usually send signals
> > by action potentials, quick voltage spikes that cause synapses to
> > transmit the signal to the recipient neurons. This is highly digital
> > in itself, although various nonlinearities in the system make it
> > possible that the interval between spikes might matter for some
> > processes.
> Then time may act as an analog influence on human (mammalian) cognition?

I'm having a flashback here to a conversation I once had with somebody
at the NYU Robotics Lab almost 15 years ago (where I was just a computer
programmer; the guy I was talking to was an honest-to-God principal

We were talking about laserdiscs (those pre-DVD LP-sized optical
videodiscs that Philips invented circa 1969, and that DiscoVision Associates
(Philips, IBM, MCA/Universal) **finally** launched commercially in 1979 ;->
(and abandoned shortly thereafter, selling the whole kit and caboodle to
Pioneer, which kept laserdiscs alive until the advent of DVD in '97).

The RF signal that ended up getting impressed on those discs was
a mixture of an FM video carrier (modulated by an NTSC composite
video signal) and a pair of FM audio carriers, "clipped" to
form something like a square wave, and then used to modulate a
cutting laser which cut "pits" and "lands" onto the master disc
for replication.

My Robotics Lab friend said: "Well, the disc has pits and lands with
sharp boundaries, so that means it must be digital."

And I said, "Well, no, because the **length** of the pits and
the **spacing** between them can vary continuously, and the laser
bounced off 'em reconstructs an analog frequency-modulated RF signal,
so it really is an analog medium."

And he said, "But that RF signal looks like a square wave, doesn't
it? So it must be digital."

And so it went. Laserdiscs really were analog, in case anybody's
wondering. DVD's in contrast, are fully digital.


Jim F.

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