[filmscanners] RE: Terms used in Dynamic Range calculations...

["Paul D. DeRocco" <pderocco@ix.netcom.com>]

Okay, I missed the "largest = maximum signal level - minimum signal level"
thing. So it sounds like you're using the word "signal" to refer to signal
plus noise, in which case the minimal "signal" is pure noise. In this case,
I suppose one could arguably say that the ability to handle a maximum of 1mW
of information while adding 1mW of noise constitutes a 0db dynamic range. In
audio, they call that (S+N)/N, instead of S/N, and it's rarely an important
distinction because usually S>>N.

But the reason I wouldn't define dynamic range that way is that if the noise
doesn't have the same spectrum as the signal, you can often extract the
signal even when its power is much less than the noise. I gave the example
of an ink jet print, which technically has a "dynamic range" of about 0db
(since the noise amplitude is full scale), but sure doesn't look that way to
the eye.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@ix.netcom.com

> From: Austin Franklin
>
> I don't understand your comment.  Both equations are identical, as:
>
> "largest" from the first equation is exactly the same thing as "(maximum
> signal level - minimum signal level)" from the second equation.  "largest"
> in the first equation is typically a "derived" term, derived from
> "(maximum
> signal level - minimum signal level)"
>
> If you have a max signal level of 10 and a min signal level of 5,
> that is an
> absolute signal level of 5, which is the same thing as would be used for
> "largest" in the top equation.
>
> Your example of maximum signal level being twice the minimum signal level
> does not say what noise is...and noise ("smallest") is the
> divisor for both these two equations.

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