Chris Hornbeck wrote:

On Dither
by Mithat Konar

(6) The results in (4) and (5) will not happen by adding noise after the
A/D conversion. Go back to our first experiment and add the random
signal to the output of the ADC. As long as the input signal is between
-0.5 and 0.5 volt, the ADC's average output will still be zero. Between
0.5 and 1.5 volts the average will jump to 1. There is no resolution
enhancement and the quantization effects remain.

I'm probably just reading this wrong, but on it's face, this is
incorrect. Digital dither is used all the time.

I know Mithat, and he knows what he's talking about. If he didn't, he
wouldn't have written it. He's not saying that dither can't be applied
in the digital domain. He's saying it needs to be applied prior to the
quantization (or re-quantization) that's being dithered.

In an ADC, this could occur in the analog domain, or in the case of an
oversampling converter, it could be done digitally before the signal is
quantized to 16 or however many bits.

In the case of truncating 24 bit data into 16 bits, he's saying you
have to add the dither BEFORE you lop off those bottom 8 bits. The
dither and the LSBs have to be summed before truncation.

ulysses