Schiit Yggdrasil -- 21 bit?


Schiit says that Yggdrasil is a 21 bit DAC. But the DAC chips that they put in the device ( Analog Devices AD5791BRUZ, 2 per channel) are 20 bit with the error of plus-minus 0.5 LSB.

How can the DAC be 21 bit if the chips are 20 bit? Using two chips per channel does reduce the RMS voltage of the noise by  a square root of 2. But how can you get to 21 bit from there?

Can someone please explain.
defiantboomerang
Awful lot of people obsessing here over measurements, one could almost mistake this for the Stereo Review website. Whatever happened to relying on A/B comparisons for what sounds better...
Awful lot of people obsessing here over measurements, one could almost mistake this for the Stereo Review website. Whatever happened to relying on A/B comparisons for what sounds better...

Plenty of folks myself included that certainly perform A/B comparisons. Nevertheless, obsessing or not, objective measurements certainly do matter.
I fear the problem is when something measures worse but sounds better. Besides the sound one hears in a particular room is due to the contributions of everything in the system - for better or worse - including the room itself.
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@davide256 

Plenty of people here disregarding measurements. One could almost mistake this for Absolute Sound. Whatever happened to understanding science and engineering instead of relying on subjective assessments of "sound quality".