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Re: SACD ultrasonic noise irrelevant...

ALL sample rate conversion generate quantization noise and artefacts - one day we will have DSPs with sufficient power (in terms of filter taps and numerical precision) to make this a non-issue, but that day hasn't quite arrived yet.

*** Why bother with a system that generates measurable noise-shaping artifacts, whether audible or not, when you can have a measuably cleaner PCM reproduction. ***

The "system" that you are not bothering is the same "system" that's embedded in just about every PCM ADC and DAC so the artefacts are not confined to DSD. Look at spec sheets.

The "measurably cleaner" PCM reproduction is because the modulation typically happens at 128x rather than 64x but the ultrasonic artefacts are still there. The only way to avoid it is to use a ladder type DAC, but that introduces other problems which is why they are becoming a rarity these days.

DSD is an interesting idea, comparable to the idea of capturing the "raw" image from a digital camera instead of converting to TIFF (PCM) or JPEG (compressed audio). There are benefits of capturing data "raw" (in this case, the undecimated delta sigma bitstream) and defer conversion to PCM, but the acquired signal is not easily editable without conversion.

However, 64fs may be good enough at one stage, but these days 128fs is the "norm" for both ADCs and DACs, and "hybrid" designs (multi-bit plus sigma delta) is common, so "raw" really should be a 5 bit 128fs bitstream rather than a 1 bit 64fs bitstream. It's kind of like forcing digital cameras to capture 1 megapixel "raw" images when the CCD is actually a 10 megapixel wafer, so the original "benefit" of DSD (not throwing away data) becomes a moot point. To me, that's a far more serious objection to DSD than ultrasonic artefacts.

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