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
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.
@shadorne and @defiantboomerang

But JA also states "Now you could say that you prefer the sound of truncation against that of redithering and I have no argument with that opinion."

Not to mention that JA’s measurement "suggest" that the LSBs of 24-bit data are simply truncated. So he is acknowledging he is not absolutely certain with his assertion/measurement understanding.

JA is super duper diplomatic or euphemistic as always.

Here is a five minute youtube that explains why dither is so important in digital audio.

https://m.youtube.com/watch?v=zWpWIQw7HWU
JA is wrong, Schiit uses rounding, not truncation.
JA believes that MQA (lossy, proprietary, licensed platform)
is " the birth of a new world".
The "extra" 1 bit in Schiit balanced multibit Dacs is deducted from the 2 phases +6dB.