That’s a positive in my book!
It is NOT really multi-bit as the fine well meaning folks over at ASR would describe it or most would think of it. It is much more unique than that.
The DSD1793 is a very unique segment DAC. The top 6 bits (or the 64 thermometer/unary coded levels), make it quite a unique DAC
I don't necessarily agree with this following assessment, but it may be helpful to think of the top 6 binary bits as now being 64 1-bit serial streams running at whatever oversample rate is in use at the time.
The lower 'binary' bits, assuming we are using 24 binary bits, goes to the 3rd order Delta Sigma Modulator. Why not just copy what was done with the top 6-bits? Bandwidth, Bandwidth, and more Bandwidth. Those 18 binary bits would equal
262,144 LEVELS!!! No chip I know of, especially not one from the turn of the 21st century can carry that kind of bandwidth.
So those lower 18 bits are sent to a 5 level, third order delta sigma modulator. Both the upper level and the lower levels are clocked at the same speed.. say 2.8mhz. The output is muxed together. The top levels are 0-63, the bottom levels are 0-4. That gives you a 2.8 mhz unary code with 68 levels (zero is not repeated) and to maintain sync, I believe either the MSB or LSB of the top level is doubled in the DSM for a 67 level code. Levels 0-66.
The top 6 bits stay bit-perfect because they are not delta-sigma modulated. The samples are simply repeated to match the clock rate. The BEAUTY of this sytem is, ALL of it can go to what ESS calls their 'revolver' system, and DCS calls their 'ring DAC'. Since all outputs are equal, any mismatches and non-linearities inherent in the cutting of the resistors is eliminated. The system is actually extremely linear, and combines the output DAC linearity of Multi-bit delta sigma along with the bit-perfect qualities of the best PCM while maintaining said linearity!
Its a really genius system, and anyone at ASR that is critical of it for being "multi-bit" with weaknesses ala 'R2R' DACs simply doesn't know what they are talking about.