iZotope MBit + Dither and Noise Shaping choices

I am using iZotope’s MBit + Dither in the Master section of Wavelab 9 to dither from 24 bit to 16 bit for CD replication.

My question is -
Using the “CD Default” preset pictured in my attachment here, the Type is set to MBit +, the dither amount is normal and the noise shaping is Ultra. What do you all think of the other noise shaping choices versus Ultra?
Ultra sounds quite good to me but I am wondering if it is adding more noise than necessary.

Any of your thoughts and opinions are appreciated. Thanks…
Screen Shot 2016-06-10 at 1.20.18 PM.png

This might be a good thread to read:
https://www.gearslutz.com/board/mastering-forum/766542-flat-dither-question-mbit.html

Alexey Lukin and Bob Olhsson are good sources for dither facts and opinions.

Thanks for the link Justin. In my search for answers I had found that discussion as well.

Yes, I believe that Alexey Lukin is the person who created iZotope’s MBit + Dither. My question was more specific - I am looking for other people’s experiences with the noise shaping setting of Ultra vs some of the other choices in MBit + Dither with Wavelab.

Quick Update for those who are interested - I wrote the creator of MBit + Dither directly and here is what Alexey Lukin had to say…

Kristin,

Ultra is adding the least audible noise of all options, but this noise
has the highest RMS level. Many mastering engineers prefer gentler
noise shaping settings or even flat TPDF dither. For example, Bob Katz
prefers light noise shaping amounts.

Regards,
Alexey

I have heard others say when using steep noise shaped dither, they have had problems with any further “processing” that could occur in the future. I have never noticed that problem myself, but maybe it’s possible… I haven’t bothered to test it. Maybe some day if I have time I’ll test it, but I don’t think it’s all that important relative to other issues… dither is SO incredibly quiet, that I believe it is one of the least important aspects of what we do (especially when working at 24-bit).

With all of that in mind, I pretty much just use TPDF with zero noise shaping.

Thank for your input, Toader. Yes, because of that I create one master for digital distribution which has low or moderate noise shaping and another master for CD replication with usually a higher degree of noise shaping depending on the music itself.

The reason I use TPDF without noise shaping for everything, is because it sounds fine, and I never have to worry about multiple masters, or about processing problems down the road.

Mbit + with no shaping and dither amount High is, as far as I am aware, pure TPDF dither.

There’s a really nice outline of dither, its types and specifically why there’s a good case for TPDF being the “optimal non subtractive dither signal” in Chapter Two of Professor Ken Pohlmann’s classic textbook “Principles Of Digital Audio”.

I agree with toader that, whilst all this is terribly interesting, it’s one of the least important aspects of what we do … at least if it is properly implimented (which mbit + certainly is).

At 24-bit it’s of minor importance (but arguably not negligible); but at 16-bit it is not merely important but essential. It doesn’t require much thought, though, because it is so clear what is optimal.

Paul