Excerpts from fons's message of 2010-06-07 23:10:27 +0200: > On Mon, Jun 07, 2010 at 10:41:07PM +0200, Philipp wrote: > > > This is probably a stupid question. > > Not stupid, but maybe worded in a way that makes > answering it quite impossible.
You managed anyway, thanks ;) > > My guess is that quantisation noise is only something present between > > the input signal and its digital representation, and hence no change of > > the digital representations can do anything about it. > > Noise shaping and dithering make sense only for 16 bit > or lower. > > For input (A/D conversion), if your converter is only 16 bit > then very probably the analog part isn't really high quality, > so even in that case analog noise will probably dominate any > quantisation noise, making the latter irrelevant. If your A/D > converter is 24 bit, then analog noise will always dominate, > so again quantisation noise is irrelevant. > > The only case that remains is when a digital signal is converted > to analog using a 16 bit D/A, or converted to 16 bit digital, e.g. > for CD. > > The purpose of dithering in that case is to convert systematic > quantisation errors (i.e. errors that would be correlated with > the signal, and therefore appear as distortion and not as noise) > to noise. In its simplest form this is done by adding noise, > resulting in a S/N ration that would be 3 dB worse than without > dithering. This completely removes any correlation between signal > and error. So the actual problem isn't the noise but its correlation with the signal? > Noise shaping and error feedback are used to avoid that S/N > ratio degradation. It works by moving most of the noise energy > to frequency regions where it matters less. > > You can see some examples of this here: > > <http://www.kokkinizita.net/linuxaudio/dithering.html> > > The last one (using noise shaping) has the worst S/N > ratio if you measure it without any psychoacoustic > weighting. But it will sound the best. I'm a bit curious about the first graph. The actual signal is the ~1kHz one, but what are all the other 'spikes'? -- Regards, Philipp -- "Wir stehen selbst enttäuscht und sehn betroffen / Den Vorhang zu und alle Fragen offen." Bertolt Brecht, Der gute Mensch von Sezuan _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
