Dither Amplitude during Silence

[DJS]

If one places a period of silence between clips in a timeline and then exports a PMI image or CD CueSheet, using dither 16bits WLC/Noise Shaper 49th Order, I get -66dB of dither noise for the silent section. This seems excessive by about 20dB! What's going on here?

[mpdonahue]

What you are seeing are the effects of noise shaping. Total amount of dither energy is the same, but noise shaping pushes the same energy into smaller bands to which are less sensitive.
Once upon a time, when digital dinosaurs roamed the land, Sonic Solutions had a dither that allowed you to choose less than one LSB of energy and switched the dither off when there was digital black or nothing below the 16th bit......I think that was in 1990
All the best,
-mark

[DJS]

Thanks Mark. I will have to dig out some quieter music and see what the dither level ends up being. Is the resulting dither level higher for silence than for quiet music? How can one realise the 90dB of dynamic range in a CD if the dither noise floor is already at -66dB? Rhetorical question, turn noise shaping off.

[fl]

Rhetorical question, turn noise shaping off.

and set to "Rectangular" (1 bit) as opposed to "Triangular" (2 bit).