[filmscanners] Re: Density vs Dynamic range

["Julian Robinson" <jrobinso@pcug.org.au>]

Austin - of course RMS measurement applies to dynamic range.  I think the
fact that you say this points to where your view differs from the rest of
the world, but I'm damned if I can work out how...

Remember the definition from the book *you* posted and *you* agree with:

>the Dynamic Range equation out of "Digital Signal Processing in VLSI":
>DR (dB) = 10log10(largest signal/smallest discernable signal)

How exactly are you going to measure "largest signal" and "smallest
discernable signal"?  Most people would use RMS, or at least try to
approach that with a mean measurement if they didn't have the true-RMS
gear.  Alternatively you could use peak measurements, but that is a bit
tricky with the noise and you have to involve some statistical assumptions,
and as Julian V says, sometimes it can change the results depending on your
choice of peaks in the HiFi world where short term peaks can be a lot
higher than sustainable peaks.

Why on earth would you say "RMS doesn't apply to dynamic range."?

Julian R



At 23:33 12/06/02, Austin wrote:
> > > SNR also is an RMS based measurements, and RMS doesn't apply
> > > to dynamic range.

Julian V replied:
> > Why not?  I've seen quite a few designers and vendors use the
> > above-described convention for specifying dynamic range.  Consumer HiFi
> > manufacturers have used other schemes, measuring the limits of their
> > products to handle impulses or "instantaneous" signals.  But usually these
> > schemes are designed to generate more impressive numbers for
> > advertisementss

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