After checking at least the first half dozen papers I linked, it should be apparent that
1) a dithered sigma-delta converter is typically better quality than one without dithering 2) dithering means adding noise to the signal (usually white noise, or a modified spectrum via noise shaping) 3) dithering adds a constant noise floor to the signal 4) dithering eliminates signal-dependent quantization artifacts, hence the noise floor becomes entirely independent of the input (*) 5) dithering is usually placed inside the feedback loop of the noise shaping (**) (*) "Such dithering, with the optimal triangular probability density function (TPDF) dither, in principle completely eliminates all distortion, noise modulation, and other signal-dependent artifacts, leaving a storage system with a constant, signal-independent, and hence benign noise floor."[1] (**) "One criticism of the 1 bit converter [...] is that because only 1 bit is used in both the signal and the feedback loop, adequate amounts of dither cannot be used in the feedback loop and distortion can be heard under some conditions.[1][2] Most A/D converters made since 2000 use multi-bit or multi-level delta sigma modulators that yield more than 1 bit output so that proper dither can be added in the feedback loop. For traditional PCM sampling the signal is then decimated to 44.1 ks/s or other appropriate sample rates."[3] ---------------------------------------------------------------- So, I would expect the overwhelming majority of sigma-delta based soundcards to be dithered, since those are better quality. Hence, RBJ's assumptions about sigma-delta converters only apply to a small subset of sigma-delta converters, namely the low quality, non-dithered converters, that are not used in modern sound cards (maybe only in some old and obsolete, pre-2000 sound cards). Therefore, my assumptions about the signal-independent, constant noise floor of converters was correct, since the overwhelming majority of sigma-delta converters are expected to use dithering. Best regards, Peter References: [1] "Why 1-Bit Sigma-Delta Conversion is Unsuitable for High-Quality Applications" http://sjeng.org/ftp/SACD.pdf [2] Why Professional 1-Bit Sigma-Delta Conversion is a Bad Idea http://peufeu.free.fr/audio/extremist_dac/files/1-Bit-Is-Bad.pdf [3] https://en.wikipedia.org/wiki/Noise_shaping -- 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
