Hi RBJ, Well, the point of dither is to reduce correlation between the signal and quantization noise. Its effectiveness requires that the error signal has given properties; the mean error should be zero and the RMS error should be independent of the signal. The best known examples satisfying those conditions are white Gaussian noise at ~ 6dB above the RMS quantization level and white TPDF noise at ~3dB above the same, with Gaussian noise eliminating correlation entirely and TPDF dither eliminating correlation with the first two moments of the error distribution. That's all textbook stuff. There are certainly noise shaping algorithms that shape either the sum of white dither and quantization noise or the white dither and quantization noise independently, and even (to my knowledge) a few completely non-white dithers that are known to work, but determining the effectiveness of noise at dithering still requires examining the statistical properties of the error signal and showing th at the mean is 0 and the second moment is signal independent. (I think Stanley Lipschitz showed that the higher moments don't matter to audibility.)
Probably there are papers around looking at analog noise in typical music signals and how well it works as self dither (because self dither is assumed in some A/D conversion) but I don't know them and would be very happy to see them. The one case I know involving some degree of modeling was a tutorial on dither given last year in Berlin that advised against depending on self dither in signal processing unless the noise source was checked out thoroughly before hand. Variability of amplitude, PDF and time coherence were discussed if I recall. Best, Vicki On Feb 6, 2015, at 9:27 PM, robert bristow-johnson wrote: > > > > > > > > ---------------------------- Original Message ---------------------------- > > Subject: Re: [music-dsp] Dither video and articles > > From: "Vicki Melchior" <vmelch...@earthlink.net> > > Date: Fri, February 6, 2015 2:23 pm > > To: "A discussion list for music-related DSP" <music-dsp@music.columbia.edu> > > -------------------------------------------------------------------------- > > > >> The self dither argument is not as obvious as it may appear. To be effective >> at dithering, the noise has to be at the right level of course but also >> should be white and temporally constant. > > why does it have to be white? or why "should" it? > > > > > > -- > > r b-j r...@audioimagination.com > > "Imagination is more important than knowledge." > -- > dupswapdrop -- the music-dsp mailing list and website: > subscription info, FAQ, source code archive, list archive, book reviews, dsp > links > http://music.columbia.edu/cmc/music-dsp > http://music.columbia.edu/mailman/listinfo/music-dsp -- dupswapdrop -- the music-dsp mailing list and website: subscription info, FAQ, source code archive, list archive, book reviews, dsp links http://music.columbia.edu/cmc/music-dsp http://music.columbia.edu/mailman/listinfo/music-dsp
