On Fri, 30 Nov 2007, Paolo Saggese wrote: > > On Friday 30 November 2007 13:15, Sergei Steshenko wrote: > >> I am sorry, but all the above said can be summarized in very few sentences: >> >> 1) any phase/frequency modulation produces a signal with infinite >> spectrum; > [...] > > well, sure... as far as one knows what all that means. I tried > to explain jitter effects in terms (hopefully) understandable by > anyone, not just by those who have some EE background. 8:-) > > Apart from that, from a purely "technical" point of view of course > you're right. Analogue W&F and other forms of "analogue jitter" (if > we like to call it such) does indeed introduce phase and frequency > modulations of the source signal, which in turn of course cause the > appearance of infinite terms in the spectrum. That's about the same > that digital jitter does when just looking at a spectrum analyzer > screen (though typical levels of "analogue artifacts" may look even > worse from that point of view). > > Nevertheless, from a "perceptual" point of view, reasonable amounts > of "analogue artifacts" (modulation) seems to be much more "benign" > to our ears (brain, actually) than most currently common levels of > "digital artifacts". Your evidence for this is what? > > That is, it looks like we can easily tolerate some relatively large > amounts of "analogue artifacts", while even small amount of "digital > artifacts" may result in a quite "unnatural", unpleasant sound. Your evidence is what? > > I guess not by chance audiophiles have long ago coined the term > "digital sound"... not as a compliment. :-) Audiophiles have also coined much other nonsense like the effect of speaker cables on the sound. Just because someone who calls himself a audiophile prattles on about something does not make it true. > > I've also tried to give some hypothesis about why it is so... > though of course they were just that, no more than educated > guesses. > > >> 4) any high end digital receiver should have a PLL-based receiver that >> resamples (with the same frequency) input signal end eliminates jitter >> - rather, the jitter becomes the one of the PLL; > > this would be another long story... way out of this list scope, I'm > afraid. > > BTW, to try making a long story short, IMO/IME PLL-based resampling > techniques does not completely "replace" the "incoming" jitter with > the local PLL one as you seem to imply. > > Resampling does indeed (usually...) reduces the overall amount of > jitter but, unfortunately, the resulting "output" jitter is still > somehow correlated to the "input" one (and, usually, to the signal > too). That is, resampling _may_ (or may not) help mitigating the > problem, but surely it can't really solve it altogether. > > A better approach is (IMHO) to try to "avoid" jitter in the first > place, by using the "cleanest" possible clock for the DAC (that is > a free, local XTAL oscillator placed next to the DAC itself), and > then to somehow slave the source data stream to that clock. Fine. But that is not a problem. As I said, ppm which is not hard to obtain is -120dB below the signal level-- ie totally and completely inaudible. > > (that's in fact the idea that made me start this whole thread. :-) > > BTW, compare the above with the "standard" approach used in consumer > devices, that rather do the other way around. That is place the clock > at the source, embed it in the data stream (S/PDIF) and then, in the > long run, eventually (and hopelessly) try to fight the large amounts > of nasty, correlated jitter resulting from so doing afterwards... No idea what this means. > > >> 5) from my experience the decisive factor nowadays is analog circuitry >> in the power amplifier and speakers, not digital jitter. > > well, yes and no. > > Analogue circuitry and speakers are indeed still the most "sensible" > parts which limits the performance of an audio systems. > > Yet this does not mean that nowadays digital sources are "perfect" > or anyway so good that their problems may be neglected altogether. > > That _may_ be true for low to average quality audio systems, but it > is by no means true once you move toward truly high quality ones. > > If you have a really good audio system, what I have (improperly) > called "digital artifacts" (of which jitter is one of the possible > causes - though not the only one) results in clearly audible and > quite annoying defects. > > Of course, again that's IMO/IME. Yes. > > To conclude, in case I was misunderstood, what I meant to point out > was not that digital audio is in itself a "step back" with respect to > traditional analogue techniques. Of course it is not. Rather, I just > meant what I said: digital audio is no magic, it does have it's own > problems and it is by no means "intrinsically perfect". > > This may seem (and should be) an obvious statement... was it not for > the massive marketing hype trying (and often succeeding) to convince > everyone of the contrary. 8-) Exactly what hype is that? The hype appears to me to be coming from the other end-- the analog junkies. > > OK, we ended up quite OT... sorry. > ------------------------------------------------------------------------- SF.Net email is sponsored by: The Future of Linux Business White Paper from Novell. From the desktop to the data center, Linux is going mainstream. 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