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
Yeah Robert Harley is with Absolute Sound he's the reviewer that got excited about the Yaggy.
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At least Stereophile try to backup their reviews with measurements and you can draw some kind of parallel between review and measurements (if you can understand them) most readers can’t, so they need to learn.

Where Absolute Sound is more like "audio poetry" wafting in the wind, but granted of late they are bending and have had "some" independent measurements done on just a little of what they review, would be good to see more of it.

Cheers George