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
I've learned to put my hand firmly over my wallet when someone starts obsessing over measurements... usually what follows is a pitch for "mid-fi" gear where there are no A/B review defenders. I do hope that the original spirit of TAS remains with this site, seeking excellence of sound and ignoring the "midfi" spec game used to manipulate novices in their  audio purchases.
defiantboomerang
Whatever happened to understanding science and engineering instead of relying on subjective assessments of "sound quality".
The two are not mutually exclusive. In any event, this is a hobbyist’s group, not an engineering forum, so please don’t insist that contributors here refrain from sharing "subjective assessments" of sound quality.
@cleeds 

A hobbyist group is fine, nobody objects to that. But being a hobbyist does not mean that anything goes. In particular, sighted listening is useless to judge sound quality. Blind tests are a but better, but to seriously judge audio quality, one must measure.
defiantboomerang
A hobbyist group is fine, nobody objects to that.
Some here have objected - very loudly - and they have insisted on scientific data to accompany observations. That's just silly on a hobbyist site.

 But being a hobbyist does not mean that anything goes.
Of course. These forums have rules, as established by Audiogon. Those rules govern the site.

 In particular, sighted listening is useless to judge sound quality.
That's opinion stated as fact.

Blind tests are a but better, but to seriously judge audio quality, one must measure.
Surely measurements have their place. But most of the great audio designers insist that listening is also important. Listening and measuring are not mutually exclusive.