Obviously I cannot answer with the expertise of Jussi or Bogi.
However, I have studied chip conversion for over a decade as a dedicated amateur. I have learned so much; enough to be dangerous and understand how little I actually know. That said, I think I have a fair understanding of how the ESS operates in spite of how tight-lipped ESS has been.
Everything you states seems to be right on. I didn't read it in depth, but what I did see, looks correct.
I am going to stick with DSD in; DSD out conversion to keep it simple.
ESS again has been tight-lipped on their method of DSD conversion, but I DID happen to find a diagram from one of their datasheets that answers a LOT of questions.
This confirms that what you may have heard explained over the years by some really high-end, well respected engineers is not really correct, or at least they were obfuscating. The truth seems to be that the DSD path is not that different from what we have come to know about things like Sony's DSD-Wide, or how Cirrus, AKM and others covert DSD with DSP/Volume Control.
The Digital Signal Path below shows what I have suspected all along. DSD hits a FIR low pass filter, which creates a multi-bit signal. The signal is not 'decimated', and remains at the same rate as DSD input. (Decimation can mean more than one thing to me; in this case I say not decimated because no samples are removed, even if there is some redundancy.) The filter output can be just a few bits wide, but IF the volume control is used to attenuate, the output of the FIR filter is multiplied by a 32bit gain control, creating an even wider sample. Due to bandwidth restraints, we are probably not in a DSD unary code; we will be in binary.
Next up DSD multibit intermediate is sent to the IIR filter that is user selectable at either 47khz, 50khz, 60khz, 70khz for further noise control before it is sent to the Delta-Sigma modulator. ( Not shown in diagram is the sample rate converter for jitter reduction, but this is likely before modulator as well, although I could be incorrect here).
The modulator works as a multi-bit DSM. Considering the DAC itself has 64 unary/thermometer elements per channel, the modulator probably operates at 6 bits (binary).
The 6 bit binary output of the Delta Sigma modulator at whatever oversampled speed is used (x128 or x256) is send to a logic system that converts the 6 bit binary into a 64 level UNARY code. ( note, that in unary code, 64 elements would actually mean 65 levels because all elements 'off' is zero. Likewise, 63 elements would be required for 64 (6-bit) levels) Furthermore, ESS uses here what they call the 'revolver' technique. (similar to DCS 'Ring' DAC). Levels are 'scrambled' since unary code is essentially multiple 1-bit signals that when added together equals the correct amplitude. It doesn't matter which element the logic 'shoot's the level to. The output elements are all equal, and this creates exceptional linearity, avoiding element mismatch.
Now HERE is where we get conversion that is similar to the DSC1 (DSC2 DSC2.5 etc).
DSC1 uses 32 equally matched output elements. Unlike the ESS which receives multi-bit delta sigma with 6 binary bit / 64 individual levels, the DSC1 receives 1 binary bit DSD. It uses shift registers to create 32 1-bit streams. All the same 1-bit stream, but each stream is offset by 1 clock cycle that, along with the output elements, form a FIR filter, which in this case, is a type of very simple moving average filter, a CIC filter. (If you ever see the output of a CIC filter on chart, you will see the null points that give it its comb filter name)
Yes, the DSC 1 design has similarities to the ESS in that both use unary coded 1-bit conversion for the DAC. The ESS however is a true multi-bit signal. The DSC1, along with many other brands who do something almost exactly the same, is really just a 1-bit signal as far as
actual information is concerned. But the method of conversion is very, very similar. The 1-bit way is less complex, and there are those who prefer as little complexity and as little DSP as possible. I am not here to say which is better, or if one party is right and the other is wrong. From my PERSONAL perspective, I would use the DSC2 with HQplayer any day. Thankfully I am lucky enough to have one of the very rare in the wild DSC2 converters.
I can reflash it all day long, but it doesn't wake up anymore.
