ralphpnj wrote: > > > The presence of jitter in digital audio is not a new issue and has been > dealt with in various ways since the introduction of the compact disc > back in the mid 1980s. >
Completely true and might I add that jitter in digital data is far older than that. I still remember maintaining a discrete-transistor PLL and buffer in a computer tape drive in the late 1960s. Same problem, same basic technology solved it. A signal sourced from magnetic media picked up jitter due to imperfections in the mechanical handling of the media. Updated SS electronics that was first implemented in octal tubes made it go away. If anybody wants to see jitter in spades, look at the output of the photodiode preamp in any CD player, if it can even be probed in a modern player. It used to be TP1. The inbound jitter is all gone courtesy of a PLL and a buffer, now a minor function of a LSI chip. > > However unless the CD player was really poorly designed and/or > manufactured any jitter present was completely inaudible, either because > the level of the jitter was well below the noise floor or because the > jitter was in the pico second range. One thing that was true is that > even in well designed and built CD players jitter was present and could > be measured. > If you want to experience audible jitter listen to LPs or analog tapes! If you want to experience jitter with modern equipment, you will probably have to break something or add the jitter yourself. I am, BTW well-practiced at that art with the pre-jittered music files to show for it. > > As computer based audio and the of USB and USB DACs took off there was > found to higher levels of jitter in the digital signal carried via a > typical computer's USB port due the digital data being transmitted in a > non-asynchronous manner. > Interestingly enough, USB jitter was well-managed without asynch protocols by USB Codec chips that were mainstream ca. 2008. The data sheets are still on the web. One problem for the placebophiles was that they were limited to 48 KHz sampling. I believe that one of them is key to the fine Jitter performance that Archimago found in one of his Blog tests of the FIIO U7. > > However, as in the case for the CD players, the vast majority of the > USB induced jitter was inaudible since either the level of the jitter > was well below the noise floor or because the jitter was in the pico > second range, except of course for those really badly designed and > poorly built USB ports, in which case the jitter might actually be in > the nano-second range (a very, very, very, very rare occurrence). > If you want fun, try to find audible jitter in well known non-asynch USB interfaces such as the eMu 0404. It is out of production now and there is no Win 8/10 support, but it is supported up to Win 7. > > Now here is where it gets really interesting and the audiophile magic > and voodoo kicks in. At some point several years ago some audiophile > guru (I believe that it was one the "well respected" high end audio > manufacturers, aka snake oil salesman) claimed to clearly hear (not just > measure) jitter in the analog output of a USB DAC being fed digital > audio data via USB from a computer. I don't know if the jitter in > question was in the pico or nano second range but in either case > anything in those ranges is completely inaudible to humans due the > limitations of human hearing based on biological science. Apparently > audiophiles have super human hearing capabilities. > If you check the annals of the AVS forum, a well known highly vocal advocate of Asynch USB and critic of HDMI participated in an ABX test related to jitter. jkeny is a close friend of his and don't expect him to bring up the results. For the record I offered additional tests with other forms of jitter (my first test was based on the most common kind of jitter I know of) but well, not so much. > > Now it was also known that by using an asynchronous USB signal instead > of a non-asynchronous USB the jitter level could be greatly reduced and > so the audiophile fixation on asynchronous USB was born. > The fact that the issue had been already acceptable resolved by other means is one of those little secrets of placebophilia, it seems. > > All of the above is a classic example of audiophile FUD (fear, > uncertainty and doubt) in it full and mighty glory. A fake problem is > introduced (audible jitter) and equally fake solution is introduced > (asynchronous USB) and the money started rolling in as all good > audiophile fell in line and waited in line to buy all those pointless > asynchronous USBs. Absolutely beautiful and a required lesson to be > learned for all future snake oil salesmen. > I seem to recall successful attempts to debunk much of this jitter FUD in Archemago's Blog. Don't wait for any of the placebophiles around here to jump up and post a link but it must be such a burr under their saddle that they can't forget. Usual placebophile deflections, eh? ------------------------------------------------------------------------ arnyk's Profile: http://forums.slimdevices.com/member.php?userid=64365 View this thread: http://forums.slimdevices.com/showthread.php?t=103684 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/audiophiles
