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
Ahh that would be Robert Harley of TAS, you can read here:
http://www.theabsolutesound.com/articles/schiit-audio-yggdrasil-dac/

Build of a Yggi here
https://www.youtube.com/watch?v=R3YZmaIRb6Q

Video review here:
https://www.youtube.com/watch?v=AFvUyK1oQRQ

Really interesting discussion with Mike Moffat and Jason Stoddard:
https://vimeo.com/194658219

I love the Yggi, its amazing for the price.

Brett

@shadorne Nice ATCs!  I've never seen those, but being familiar with ATC, I can guess they sound pretty amazing from an analog front end!
@shadorne 

The specification in itself is honestly rather vague, which is another gripe the entire industry as measurements must be standardized to permit consumers to compare. Far too many brands take liberties with specifications. Sure, it could be set out to lessen consumer confusion when providing only what is deemed necessary, but when a specification is incomplete such as the one listed on ATC's own website, its best to leave it out instead. 
Back to Yggdrasil, my worst fears as posted above are true.

I found this statement in Stereophile

"When you have 24-bit data but 20-bit DACs, you need to dither those data to match the DAC. Otherwise, simply chopping off the 4 LSBs, called "truncation," reintroduces quantizing distortion. Schiit’s Jason Stoddard has subsequently said that the Yggdrasil "rounds" 24-bit data but my measurements suggest that the LSBs of 24-bit data are simply truncated.

John Atkinson
Editor, Stereophile"

This is a disaster. Every studio mastering engineer will carefully dither high resolution 24 bit data when converting to 16 bit lower (bit depth). This is in order to reduce quantization noise! This is not optional - This is industry best practice! If JA is to be believed Schiit do NOT understand digital signal processing at all - they just truncate the data!!! They may be geniuses at headphone amplifiers and analog circuits but this product is a failure if you are interested in high fidelity.

Be warned - this DAC should only be used with files that are 20 bit or less. If you use a PC for playback to this DAC then I would recommend doing a proper dithered conversion of 24 bit source files to 20 bit on the PC prior to sending to this DAC as it will sound much better. Programs like Audacity can do this conversion for you.