Honestly I don't even think it is.
Question from my side: If the RU7 uses some kind of SRC chip for the conversion, isn't this just a DSD DAC?
Why not call it a discrete DSD DAC? Oh, maybe licensing...
While Cayin didn't elaborate, RU7 (and N7) discrete 1 bit DAC design seems to be directly descended from Signalyst DSC1 (*the first open hardware design of its kind as far as I know) - and Signalyst DSC1 release date is well documented at April 18th, 2014. The design didn't go mainstream for a few more years, or you can even say it hasn't really go mainstream yet.
The SRC chip is there to convert all incoming audio data to DSD format (*which is digital to digital conversion, or transcoding), but it doesn't do the Digital-to-Analog Conversion. That's the job for the 1 bit discrete circuit. RU7 is in every essence an DSD DAC since '1 bit' is mentioned. I am assuming Cayin wants to keep the focus on 1 bit because many DAC chip out there that can decode DSD is not purely 1 bit chip. They are often multi-bit PCM chip that do internal DSD-to-PCM conversion automatically without user knowledge. So saying a DAC that can do DSD doesn't automatically make it a 1 bit chip, but a 1 bit DAC chip is however always a pure DSD DAC.
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