Re: "analog computer" = useless hypothesis?

From: James Rogers (
Date: Sat Mar 31 2001 - 20:54:53 MST

On 3/31/01 3:57 PM, "Jim Fehlinger" <> wrote:
> The analog/digital dichotomy, both at the macroscopic level of
> actual physical computers (including CD players and DVD players!)
> of the present day, and at the hypothesized "quantum foam" level
> of reality, is a paradoxical one. The "digital" nature of
> any real machine is an idealization, an abstraction -- if you
> hook up an oscilloscope to the innards of a computer, you
> see things happening at the **analog** level -- square waves
> aren't perfectly square; they have finite rise and fall
> times, etc.

Most of the claims regarding analog are only true if one is willing to
assume a noise floor of zero (which yields an infinitely high
signal-to-noise ratio). In the real world, this is obviously not the case.
For an analog system of any given resolution, it is trivial to calculate the
parameters of a digital system that will give equivalent or better signal
resolution. People tend to forget that noise in analog systems defines the
effective signal quantization in the same way bit-depth defines it for
digital systems. Sure, you can measure variations in signal below the noise
floor, but who cares, its *noise*.

That noise is used to improve signal resolution is red herring. No signal
is actually gained from dithering (it changes the nature of the noise floor,
not the location) and it actually lowers the SNR, though most systems today
have so much headroom that they can afford to burn a few dB making the noise
subjectively more pleasant. There are ways to effectively increase
bit-depth using noise, but these are purely digital domain tricks
(converting unneeded sample rate capability into more effective bit-depth).

> These are extraordinarily suble issues, which the most brilliant
> minds in the world have yet to come to grips with completely.
> There's no point in trying to divide this list, or any
> other realm of discourse, into tribes of "analogists" and
> "digitalists" and then picking sides.

I don't think there can really be an argument with a fully informed crowd.
All the arguments I've seen on "analog" versus "digital" have been grounded
largely in ignorance of what these things actually mean in terms of
measuring/using/converting a signal.

> If you want a real rip-roaring battle between two such camps
> (which you may get tired of after a time, I warn you ;-> ),
> look up the LP vs. CD wars which have raged on the
>* newsgroups, if and when Google gets the
> Usernet archives back on line.

The LP versus CD wars (long since dead) were a classic example of people
confusing the limitations of a given implementation and the actual
limitations of the design. Early CD implementations actually had a lower
SNR than very high end analog systems. However, current implementations
exploit most of the bit-depth of the CD, giving an SNR on a cheap system
that has 20+dB over the finest analog recording devices. You can't argue
with that.

-James Rogers

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