PMD100 is one of the few digital filters with variable dither levels. There are 8 dither modes available in PMD100 program mode. Here is the description from the datasheet:
Modes 0 and 7 are minimum amplitude dithers which correct quantizing errors only, whereas modes 1 through 6 are increasing levels of high-frequency weighted dither designed to smooth out non-linearity errors in multi-bit DAC’s (Modes 0 or 7 are appropriate for single-bit DAC’s).
I made some measurements to see how the dither modes work. I used the same PCM1702+PMD100 DAC as in here.
This is the dither setting (mode 0) available in PMD100 stand-alone mode.
Quite a lot of "grass" but at levels that are probably not audible.
Here is the dither mode 6 which according to datasheet should work well with multi-bit dacs.
Most of the "grass" is gone.
Modes 0 and 7 are minimum amplitude dithers which correct quantizing errors only, whereas modes 1 through 6 are increasing levels of high-frequency weighted dither designed to smooth out non-linearity errors in multi-bit DAC’s (Modes 0 or 7 are appropriate for single-bit DAC’s).
I made some measurements to see how the dither modes work. I used the same PCM1702+PMD100 DAC as in here.
This is the dither setting (mode 0) available in PMD100 stand-alone mode.
Quite a lot of "grass" but at levels that are probably not audible.
Here is the dither mode 6 which according to datasheet should work well with multi-bit dacs.
Most of the "grass" is gone.
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It's effectively turning small signal data into pseudo-small signals and makes the DAC rely on its thermometer segment so it's a form of feedforward (opposed to sigma-delta). Didn't help with MSB nonlinearity expectably (scrambling, DEM does that).
