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

[Erik de Castro Lopo]

On Tue, 22 Apr 2003 19:54:09 -0500
"Dustin Barlow" <duslow at hotmail.com> wrote:

> I read an interesting article on Direct Stream Digital (DSD) / Pulse Density 
> Modulation (PDM) entitled "A Better Mousetrap" by Brian Smithers in the May 
> 2003 issue of Electronic Musician.  Since, Brian did a good job explaining 
> PDM/DSD in quasi-layman terms, I'll just quote snippets from his article to 
> set the stage for my questions.

<snip>

> DSD/PDM appears to be a superiour technique for recording and playing audio 
> material.  

Having been around digital audio and digital signal processing for over 10
years, I am still far from convinced.

> Granted, this technology may never catch on because of all the 
> hardware and software changes that would be required to mirror what a 
> typical PCM based DAW currently does.  But, if DSD/PDM does catch on, and 
> DAWs start being produced, how will this effect current audio DSP 
> techniques?  

I have not looked into the maths behind algorithm development in DSD/PDM,
but I doubt it is anywhere near as easy as with PCM.

> The article mentions a program called Pyramix (Windows) which features DSD 
> support.  However, for Pyramix to do EQ, dynamics, reverb processing, and to 
> display waveforms and vu levels, it converts DSD to a "high quality" PCM 
> format.

That should tell you something :-).

> I suspect that if DSD/PDM has any hope of succeeding in the current DAW 
> world, there will have to be some real-time lossless converter constructed 
> to seemlessly bridge the formats.  

The problem I see here is that the PCM->DSD and the DSD->PCM conversions
would probably both incur a time delay. That makes real time processing 
very difficult.

> But that of course begs the question of 
> why use DSD in the first place if you just are forced to "decimate" it PCM 
> to process it?

Bingo!

> Sony is currently using DSD/PDM in their SACD format, and are positioning 
> themselves to be the competing format to PCM based DVD-A.  

Yep, I believe that this has more to do with marketing and market positioning
that anything else.

> The fact that 
> something like this shows up in EM means that at some level the format is 
> being given some credence and is being watched by others then just the 
> audiophile recording crowd.

I believe that it is being given credence because it has Sony behind it. If
this was being pushed by some some company noone had heard of, it would be
guaranteed to dissapear without a trace.

> Is DSD/PDM just a flash in the pan, or does it really represent a new wave 
> of thinking regarding storing/processing audio data?

I go for option 3. Its marketing.

Erik
-- 
+-----------------------------------------------------------+
  Erik de Castro Lopo  nospam at mega-nerd.com (Yes it's valid)
+-----------------------------------------------------------+
Complex problems have simple easy to understand wrong answers.