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
David and dhal:
I think it will be at least a week before I can discern how closely the Yggdrasil approaches the sound of live music. Mine arrived earlier than I expected: when I checked the tracking, it had already been routed to the local Fed Ex office, so I picked it up early this AM, and, of course, plugged it in immediately, and played it. I did this even though I KNOW I won’t hear anything new, because I just bought the Transparent SPDIF cable yesterday afternoon, and it, too, will have to break in (no other choice: haven’t had a DAC since the Bryston BDA-2 and sold the last coaxial cable long ago). No matter. I will still enjoy hearing the sound blossom. The only thing that was surprising to me is receiving an email from someone at Schiit, saying that they did not believe in "burn-in" time. This, especially given that Robert Harley, in his TAS review, wrote "Although Moffatt warned me that the Yggy wouldn’t sound good right out of the box, I gave it a quick listen anyway after an hour of warm-up. He was right; the Yggy was hard, bright, forward, and flat. I checked in with it a couple of times over the next week and heard it improving somewhat, but it was still disappointing." So I’m unclear if there was more to the conversation, but that Moffatt only meant that until the unit’s thermal whatever-it-is reached optimum temperature, that it wouldn’t sound good. Harley clearly didn’t like it even after a week.
And this is why I only use my own ears and why I don’t compare components (or use measurements): for me, only the sound of a live instrument has a reality that is indisputable. And, as I said, I’ll look at the specs, but I’m always going to go with "how close does this sound to a live cello/guitar/harmonica" or whatever, despite the fact that these instrument are recorded, and very little that is recorded sounds like ’the real thing.’ either. But heck, anyone who listens to a stereo knows it isn’t going to sound like the real thing. The only thing for me is, again: ’How Close’?

The Boston Pops RCA CD under Fiedler sounded the same as it did without the Yggy, as did Yma Sumac, the Rolling Stones, and Chesky Records System Setup and Surround Sound CD, and so far, it’s been 5 hours. I got to listen for 10 minutes this morning before I had to leave the house, and while It didn’t sound "bright," I had just plugged it into my NAD integrated, which I like quite a bit. I was going to involve the CJ setup, but decided against it, since I’d been using the NAD the past few weeks for checking room acoustics and the Townshend Seismic platform and pods, and don’t want to introduce other variables into the listening the first week. The ONLY thing I could tell is, that, despite the newness of the Transparent cable and the Yggy, the organ on the Chesky CD was distinctly more powerful than before the Yggy. I guess I AM going to do ONE thing additionally, in a few days: plug in the Nola Thunderbolt subwoofers to the second preamp-out of the NAD, just so I can get an idea of what the deep bass is like. I expect that THAT should be quite the thing to play at midnight tomorrow night! Either that or the 1812 Overture on Mercury Living Presence just to hear the (actual) cannon they used!

@gbmcleod I’m in the camp that finds the Yggy needs time to break in. A week will be a good start. I suggest 3 weeks. (This is for a brand new Yggdrasil).
David, I agree.

Anecdotally, last night, I had friend over who ONLY LISTENS to the Chicago Orchestra’s Scheherazade. ONLY. He replied, upon prompting, "I think it sounds pretty good." I said, "We’ll listen tomorrow morning and we went to sleep.
We heard it again this morning and it had lost some of the dynamic compression, which Dave heard immediately. 3 days down, 5 to go. Nordost takes a month.I’d be ungenerous - not to mention foolish - to not allow the Yggdrasil its full time to blossom. I hear small vaporizations of dynamic compression, especially on lower midrange instruments. Fear not, it’ll have as much time as it needs.

IMO, whenever you plan to listen - even after break-in - it's nice to have run the Yggy with a source for 30 minutes to an hour prior to your listening session.