[LAD] [linux-audio-dev] Direct Stream Digital / Pulse Density Modulation musing/questions

Erik de Castro Lopo mle+la at mega-nerd.com
Mon Sep 24 01:28:17 UTC 2007

First off, why are you reprising a 4 year old thread if you don't have
anything new to add?

Maitland Vaughan-Turner wrote:

> So..?  Most PCM converters utilize a 1-bit stream also.  Why not
> utilize all the tools available for the task at hand?

Yes, but you need to analyze what you are doing or the next thing
you know you are paying mega dollars for triple gold plated single
direction, rare earth metal interconnect cables and other such
snake oil.

> As for processing, you can look at a PCM representation of a waveform
> to ease the processing load and then just apply the changes to the
> orignal DSD stream without ever having to process in the 1-bit domain
> directly (which is way more processor intensive since you have to look
> at a huge chunk of the stream in order to extract the amplitude data
> that is available in each multi-bit sample).

Problem : the conversion from DSD and PCM is lossy [0], hence doing
DSD -> PCM -> DSD -> PCM is a bad idea.

> IMHO, though, the hippest alternative at present is to process a DSD
> stream in the analog domain and re-record it to DSD.

Two problems:

  - A-to-D converters are limited to about 20 bits of SNR due
    to things like silicon junction noise and those noisy 
    electron thingys.

  - All commonly used audio A-to-D converters are 1-bit so every
    time you go to analogue and then into a digital effects box
    you are doing another DSD to PCM conversion.

See reference [0] below.

>  This results in a very "analog" sound.

So, you have a way of objectively measuring how "analog" something
sounds? I'd be interested in hearing your methodology.

>  These days you can get analog gear with a
> respectable dynamic range for a song (Mackie Onyx anyone?).  When you
> can get a 130 dB S/N ratio in the analog domain you really don't lose
> too much converting back and forth from 1-bit domain.

Where is you analogue to digital converter which also has 130dB SNR?


[0] Why 1-Bit Sigma-Delta Conversion is Unsuitable for High-Quality 
    Stanley P. Lipshitz and John Vanderkooy

Erik de Castro Lopo
Fundamentalist : Someone who is colour blind and yet wants everyone
else to see the world with the same lack of colour.

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