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This Post Has Been Edited by the Author
In Reply to: RE: Are you saying that 1-bit DSD and PCM sigma delta conversion are the same? posted by Chris from Lafayette on July 19, 2017 at 00:53:15
Nothing has changed since 2015, and there's no such thing as a "PCM Sigma-Delta Converter". PCM is an acronym for Pulse Code(ed) Modulation, and PDM for Pulse Density Modulation, also referred to as PWM (Pulse Width Modulation).You'd have to ask John what he's talking about, but as I read it, there's two possibilities:
1- He's substituting the acronym PCM for the actual PDM (two very different formats), in which case his argument makes some sense.
2- He's conflating two independent processes and calling that a "PCM sigma-delta" converter. The first process, (on the A/D side), is the Delta-Sigma modulation of the audio signal producing either multiple Pulse Density Modulation (PDM) bitstreams (multi-bit PDM, which John's naming inaccurately multi-bit PCM), or much less frequently a 1-bit PDM bitstream (DSD), as with the Grimm A/D Converter. If PCM is desired/required, then these PDM bitstreams (1 to 8 typically) are then followed by low pass filtering (decimation) and conversion to parallel X-bit wide Pulse Code Modulation binary words. That latter process is most certainly a lossy process. Once decimation filtered, you can no longer reconstruct the original PDM (DSD if 1-bit) bit stream.
But so what? My original statement was, and remains that all acoustic audio recordings are made using A/D converters, and the vast majority of those A/D converters are all front ended with Delta-Sigma modulators, producing an actual DSD 1-bit bitstream (as with the Grimm A/D), or from two to eight parallel (multibit) bit streams of Pulse Density Modulation. And, any conversion to any other format for whatever reason (typically post process sweetening and/or conversion to a deliverable format) is a post process from the original A/D PDM bitstream(s) conversion, and is lossy. So, if you can archive the original A/D conversion before performing the PDM to PCM/whatever format, why not do so for future processing possibilities? And especially, if you have the option, why not do those format conversions offline using more powerful conversion algorithms with more powerful processors than are available in the A/D converter box?
Seems self evident to me. But on the other hand, I don't have products to sell, or customers to convince.
Edits: 07/19/17 07/19/17Follow Ups:
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