Hi,
"DSD Wide" is not PCM. It is a multi-bit (8) two level Pulse Density Modulation pulse stream, like 1-bit two level PDM, where there is still no quantized value ala PCM, but a 8-bit word based relative value from sample to sample like 1-bit two level PDM (DSD), where there is a binary relationship between the 8 bits. Therefore there is a binary weighted relationship between samples that is processable in a computer. Of course PDM has to operate at a much higher sampling rate than PCM, relative to the signal bandwidth, to allow enough samples to recognize the fastest transients. PCM is a frame/sample based system of 2's compliment binary format of actual amplitude values. It is MUCH less efficient than PDM due to all the redundant data carried from sample to sample, and therefore less resolution than PDM for the same data rate. It's the primary no one outside audio uses it.
It sounds like you are describing DSD-wide as DPCM, as opposed to LPCM? Either way, it is still PCM, but DPCM can encode equivalent information at less bits with higher sample rates. This is related to Delta modulation, but I don't think it technically qualifies as true multi-bit delta sigma.
An area of high concern for me with DSD-wide is the impulse response. I have the white paper, and have read it multiple times. 1 bit to multi-bit conversion is done with a FIR filter, not unlike what you will find in a typical Delta Sigma DAC. The difference is no sample rate decimation happens, only the digital filter that sums to multi-bit and low pass filters the signal.
My concern is that this filtering leaves its mark. Even though it is not decimated, it has an impulse response of around 96khz, which is very much PCM like. And there is 'gentle' frequency filtering applied in the conversion. I do not know the cutoff. I do have the tap/coefficient information. Some one much more knowledgeable than I could figure it out.
So in the end, you get filtering/ringing anyway, even if there is no actual decimation applied. It is possible, though, that this CAN be minimized with gentler filters that have better impulse response. But in the case of DSD-wide, that impulse response leaves me worried...
Thanks as always, though, Tom for your great work. All the above is purely academic. The bottom line is the results you guys get from your efforts to record in pure 1 bit speak for themselves. Great stuff!!
Andrew