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In Reply to: you missed out on my last paragraph posted by Christine Tham on November 24, 2005 at 20:21:53:
that you never mention is that these DACs generate noise, but there is no signal whatsover at these frequencies so that the noise can be removed with no worries. And as you say, it is.With DSD, the high frequencies by design carry signal as well as noise, where S/N declines dramatically and eventually falls to zero, but somewhere above 50 kHz. Presumably, this high frequency signal is audibly important, otherwise why would it be designed into the system. Therefore, filtering higher frequencies costs information in DSD and is not a good approach.
Follow Ups:
not correct. sigma delta modulation generates quantization noise throughout the whole frequency spectrum. noise shaping in the converter then determines where to shift this noise. so your explanation is overly simplistic.*** Presumably, this high frequency signal is audibly important, otherwise why would it be designed into the system. ***
I think you presume too much. From what I've read, Sony/Philips seems to be implying that the advantage of DSD is the avoidance of decimation filter in the A/D stage, and the avoidance of oversampling or brick wall filters in the D/A stage. As far as I know, no one has conclusively proven that reproduction of frequencies beyond the range of human hearing has any benefit. Indeed, many experiments, both formal and informal, suggest otherwise (for example, read Griesinger's article).
Although it's not about frequencies outside human hearing range.Filtering the DSD bitstream after da conversion leads to less noise and higher in band resolution at the cost of lower bandwidth.
However every 1bit digtal system stores information about the signal across it's entire passband.
Filtering throws away information.
The trick is that according to the Philips engineers this lost information falls outside the human hearing capabilities.
(Frequency range and amplitude range)
.
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