[sdiy] Sigma Delta DSP

[Eric Brombaugh]

Here's a link to a synth-diy delay line based on a home-made Sigma-Delta 
converter and an old 1-bit DRAM:

http://www.all-electric.com/b&c.html

This design uses a simple 1-pole integrator as the DAC - just as you 
mentioned and could easily be extended to modern DRAM chips with the 
kind of storage you need.

You're right though - doing any kind of processing other than editing on 
the PDM sample stream is pretty tough because the value space is so 
difficult to analyze. You could design logic to convert the PDM stream 
to PCM and and then do traditional DSP on it, but that kind of kills the 
advantages.

Maybe you could push the frontiers of human knowledge out and do some 
research here - seems like it's wide open for new development.

Eric

Dave Krooshof - dendriet.nl wrote:
> Hi List,
>
> I was wondering weather anyone here has knowledge about
> sigma delta processing. We allready bought a AD convertor,
> and we are interested in using the bitstream output directly.
> Converting back to analog is nothing more then a low pass, so
> that is easy.
>
> Since you can edit sound clickfree in a bitstream, pitchshifting
> without taking care of windowing/granular is interesting.
> Hardwarewise, we need a delay, that can delay about
> 300000 samples and can be set to any delaylength at any time
> to do DSP directly in the bitstream. Does anyone know of
> such a chip?
>
>
> The downside however, is that I would not even know how to
> do gain properly in a bitstream, let alone filtering.
> I do have a good understanding of the SA-CD like audio signal itself.
> And I know quite a lot about statistics and calculating probabilies.
> Yet, how to do DSP in a bitstream is still vage to me.
>
> Can anyone point us to information about bistream DSP?
> Did anyone here program any bitstream DSP application?
>
> Thanks!
>
> Dave
>
>
> -- 
> http://www.dendriet.nl