Dither Plugins and Level Meters

If I play a high level file and intentionally raise the Master Section faders so that the Master Section meters and the Level Meter are well into the red above 0db, I’m getting different results in the Level Meter depending on what dither plugin I then insert during this playback:

If I insert Internal Dither - no change in Level Meter (peaks still showing above 0db).
Izotope Dither - no change in Level Meter (peaks still showing above 0db).
UV22 - peaks above 0db are blocked in the Level Meter (as I expected for all three dither plugins).

If I then render all three of these to 32 bit float, the results are the same as they are in the Level Meter. (Internal dither and Izotope dither files have level peaks above 0db, but the UV22 file is brickwalled at 0, as i would expect in any normal fixed point renders.

Why are the Internal dither and Izotope dither plugins different from the UV22? Are one or the others correct or not correct? I haven’t tried this yet in another program to see how they treat metering after dither plugins.

AFAIK, UV22 only adds noise, and does not perform noise shaping.

Thanks PG. But the other two plugins still meter (and render to 32 bit float) the same with noise shaping off. (levels well above 0db). The UV22 has nothing above 0db in a 32 bit float render. (well, it has a tiny bit but nothing like the others.)

Shouldn’t the Level Meter reflect how they’re going to be in a 16 bit or 24 bit render? (brickwalled at 0db).

Or is it better to see what it would be if it wasn’t fixed point? Maybe it’s all academic because levels shouldn’t be that hot at that point anyway, but I wondered why they would be different.

Simply, the UV-22 performs clipping, while the other plugins don’t (WaveLab will do it, if you save later to 16 bit).

Thanks PG. Fwiw, I notice it wasn’t performing clipping in Wavelab 6. Apparently that changed with the UV22 in Wavelab 7.

Note that this behaviour in on the plugin side, not the WaveLab side.