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
"How can the DAC be 21 bit if the chips are 20 bit?"

It can’t. John Atkinson review of the DAC clearly states that while the analog performance is excellent, the digital performance is less than desirable especially on high signal levels (which is the majority of pop rock music).

I wouldn’t want this DAC but I understand many here do not care about measured performance as long as they like the sound.
@shadorne 

I understand many here do not care about measured performance as long as they like the sound.

Yes, I am becoming aware of that. Could one say that such measurements-don't-matter audiophiles are like junk food addicts? They like to eat what tastes good to them without caring about the ingredients in their food?
@defiantboomerang 

Yes but I would say most audiophiles are dining on delicious gastronomic meals full of flavor and expensive ingredients rather than junk food.

I am interested in the accurate reproduction of the source file or music as produced by the artist and their engineers/producer but I fully appreciate why others like things to sound the way they want. After all at a restaurant you often order the dishes that you like best not necessarily what the chef has specially prepared.