It's a matter of definition, as you probably realised after launching this
post. "Resolution" as audio folk use it these days no longer translates into
noise. It is used to denote the word length which the converter can accept
without becoming undithered. A 16bit converter fed 24 bit signals will
distort. When these are first dithered to 16 bits (and the converter is
linear) the distortion goes away. I've gotten used to that definition, hence
the statement. But in fact, you're right - this definition becomes
meaningless since the application of that definition gives "infinite
resolution" when dithering is correctly carried out.

Since resolution - for lack of proper standardisation has become such a
volatile item, one could propose that in addition to the "commercial
resolution", another, standardised spec be added as a fixture to data
sheets.
The most stringent definition would be ENOB - equivalent number of bits,
used to quantify noise, dnl and inl in one go. In audio this could be
derived from the worst-case THD+N.
A more common definition would be translating the unweighted DR into bits.

Any other suggestions? How to handle gain-ranging converters? Etc.
Constructive comments welcome. Others discouraged.

"Stewart Pinkerton" wrote in message
...
On Mon, 22 Dec 2003 23:20:54 GMT, "Bruno Putzeys"
wrote:

I like to put it as "a correctly dithered converter has an infinite
number
of bits in resolution"

I shouldn't, if I were you! In a linear system, resolution and dynamic
range are inextricably linked.

If you take a perfectly linear 16-bit converter, you can feed it a 24 bit
signal and through dithering reproduce it faithfully.

No, you can *not* reproduce the dynamic range.

If the 24 bit signal is correctly dithered, the system resolution is even
higher.

No, it isn't!

Noise is a different affair. If it's decorrelated it's noise. Any current
24bit converter has noise above 20 bits.

Very true, and this limits the resolution to 20 bits, regardless of
*narrow band* linearity below this level. Yes, you can recover tones
at anything up to 20dB below the noise floor, and they may be quite
undistorted, but this is not resolution in the universally accepted
sense, which is a function of full-bandwidth dynamic range.
--

Stewart Pinkerton | Music is Art - Audio is Engineering