[filmscanners] Re: Density vs Dynamic range>AUSTIN (2)

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

Austin,

Here is a labored sequence of points to which I would appreciate your
response - maybe it'll help things.

For others, this is about Dynamic Range or "DR" below.

Here we go.....

Previously you promoted a definition of Dynamic Range by saying:
"the Dynamic Range equation out of "Digital Signal Processing in VLSI":
DR (dB) = 10log10(largest signal/smallest discernable signal) " ..Eq(1)

I have called this ... Equation(1) or Eq(1)]

You quoted this, and you agreed with it.  I too agree with this and it is
standard in textbooks.

1) Do you still agree with this?

Removing the logs we get

DR (ratio) = largest signal/smallest discernable signal ...Eq(2)

2)  Do you agree with Eq(2)?

We were subsequently discussing a little example as follows:

>Julian:  This example system for some reason has a noise of 1V, a smallest
>discernable signal of 2V and a largest signal of 10V.

You often tell me that noise and smallest discernable signal are not
necessarily the same thing and I agree with you.  In this example they are
different to make clear the distinction between all these values.

Now, could you please substitute the relevant figures from our example into
Eq(2)?

I'll do it here:
DR = largest signal/smallest discernable signal
         = 10/2
         = 5

That is, the dynamic range of our example system is 5.

3) Do you agree with this?

In responding to this example in a previous post, you said:

Austin:
>DR = ((max - min) / noise)
>The absolute range is 10-2.
>so... (10 - 2) / 1 or 8 is the dynamic range.

You calculated a dynamic range for the same example of 8.

4) Do you agree that 8 is different from 5?

Your new equation for Dynamic Range that you used here is:

DR = ((max - min) / noise)  ...Eq(3)

5) Do you still agree with this?

6) Do you agree that Eq(2) and Eq(3) are different?

7) If you agree they are different, then this explains why you say the
example dynamic range is 8 and the definition that is used by everybody
else uses gives a dynamic range of 5.  And thus you are agreeing that you
are using a non-standard definition of dynamic range.

8) If you do not think they are different, will you please rewrite Eq(3)
using the terminology that is used in Equation (2) - that is, rewrite your
equation (3) in terms of the two quantities "largest signal" and "smallest
discernable signal"?  Do you agree this cannot be done?

9) Do you agree that the definition of dynamic range in the book (Eq(1))
does NOT contain any mention of value "noise"?

10) Do you agree that your personal definition of dynamic range  (Eq(3))
DOES contain the value "noise"?

11) Do you agree that the definition of dynamic range in the book (Eq(1))
means that Dynamic Range is, in the general case, independent of noise?

12) Do you agree that your definition (Eq(3)) is always dependent on noise?

13) Do you agree that your definition (Eq(3)) is quite different from the
book definition?

I look forward to your response which must surely flush out where and why
we have this very fundamental difference.

Julian










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