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

Alfons Adriaensen fons.adriaensen at alcatel.be
Mon Jul 28 11:30:01 UTC 2003


On Mon, Jul 28, 2003 at 04:01:31PM +0200, Anders Torger wrote:
> On Monday 28 July 2003 14.59, Alfons Adriaensen wrote:
> > On Mon, Jul 28, 2003 at 02:00:41PM +0200, Anders Torger wrote:
> > > It becomes even more interesting when you bring in dither. Then you
> > > can represent signals whose amplitude is less than one bit, and you
> > > can increase time resolution to infinity.
> >
> > Time (phase) resolution *is* already infinite, even without dither.
> > The quantisation of time and amplitude are two completely different
> > beasts.
> 
> Well, not exactly. I'm am by no means an expert on dither, so if I have 
> wrong, let me know.
> 
> Think that you are sampling a sine wave, without dither. Truncating to 
> an even sample can result in a small phase shift after the 
> reconstruction, which is not there if you make a properly dithered 
> recording. Thus - dither improves temporal resolution, through 
> improvement of amplitude resolution.
> 
> Am I right?

Yes, in that sence you are absolutely right. The point I wanted to make
is that sampling by itself does not introduce any quantisation of the
time axis - in the reconstructed signal, the places that correspond to
the sample points are not 'better' than the parts in between. 
Some people *do* believe such things...

-- 
FA





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