[sdiy] Information Content of Signals

[Tim Ressel]

I have also wondered about this, but from a different
direction. I want to know how they can get 53kbps on a
phone line with 3khz bandwidth. Oh I know they use
this funky phase-constellation thingie. 

I have heard that they stopped at 53kbps not because
of the limitation of phiscics, but because the FCC set
a limit there. 

This kind of thing makes my brain hurt.

--Tim


--- Grant Richter <grichter at asapnet.net> wrote:
> As a point of interest, I have been trying to
> understand the theoretical
> information content of signals. Contemplation of
> this has led me to a
> paradox, and I wonder if anyone can shed light on
> this.
> 
> Information and thermodynamics are linked together
> by the expression of an
> information "bit" in a thermal sense. The best
> definition I have found uses
> Boltzman's constant (minimum energy required to
> create a new thermal state
> at temperature).
> 
> Using room temperature and the reference of 0 dB = 1
> milliwatt, the
> theoretical information content of a 1
> milliwatt-second signal would be
> (approx) 2^64 bits per second. So for sample rate of
> 192 kHz (~2^18)
> theoretical bit depth would not exceed 2^46 (64-18).
> 
> The paradox comes from the idea of over-sampling a
> thermally maxed out
> information channel. What information would then be
> gathered? Would it be
> merely redundant information, or would the waste
> heat of the conversion
> apparatus become a new signal generator?
> 
> Note that from an information theory standpoint,
> thermal noise is a
> naturally occurring signal (reverb tail of the Big
> Bang?) mixed with the
> human generated signal.
> 
> Any speculation is appreciated.
> 


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