Experiences with SlimDevices Squeezebox.
"Jitter" as a concept does not apply to digital bitstream read from a hard disk file. It was something that applied to Audio CDs but once you rip the file to a wav or FLAC it's "frozen in time." Every time you play it back in a pure digital passthrough mode from your computer, as it leaves the pc it is an exact duplication of the bitstream read from your CD at the time you read it. That's not to say that this has no jitter, it just has the exact jitter at the time of the rip, ever time. This is assuming you have a clean digital line to your outboard DAC / Pre-pro / Receiver / whatever. |
For those interested...here's a great discussion about jitter: http://www.digido.com/portal/pmodule_id=11/pmdmode=fullscreen/pageadder_page_id=28 |
Sonance...I posted your response in another forum and Tonycdk replied in the following manner; "Having a correct bit stream is not the problem . Almost all players derive the correct bit stream (except for read errors that may occur from really bad CDs). Accurate digital reproduction requires that the original sampling of the analog waveform from the microphone occurs at exactly equal time increments, and then is converted back from digital at exactly equal timing increments. If there is any slight variation in the timing, either in the recording process or the reproduction process (the two are independent of each other) the reproduced waveform will not be exactly the same as the original. It is basically more or less impossible to build hardware to provide absolutely perfect timing. The slight scatter in the actual length of the timing ( it is usually in the hundreds of pico second range) results in what we call "jitter" and a slightly imperfect waveform reproduction. In any digital recording there is absolutely nothing we can do about 'jitter' introduced by timing spread in the recording equipment. This effect is encoded on the recording and can not be removed. Fortunately most recording gear seems to be reasonably good these days - although that may not be the case for some early digital recordings. Mostly, what we hear as 'jitter' results from the accuracy of the timing in our gear. Having a perfect bit stream does not affect the timing. This is why we put so much emphasis on accurate clocking of the data stream - for example, why so many of us use the Big Ben for re-clocking. The short answer to your question is that having an accurate bit stream is good, but is unrelated to the jitter issue." This is why reclocking the signal pertains to the squeezebox even though the data stream originates from a hard drive!!! |
That fits with my understanding of the issue, I think. Jitter can occur at any point in the chain but can be put back in its right place by clocking it right - which is the purpose of the Big Ben (I want one!), but of course jitter in the recording process cannot be fixed in the playback process or vice versa. The added jitter I thought I experienced with WiFi was possibly power supply issues when using WiFi causing the crystal clock in the Squeezebox to operate less effectively. Just on this jitter issue - I am no engineer, and what I am about to say will probably anger anyone who is, but my playing with stuff is unbounded, and I think there are possibly other issues than just hitter at play in digital cables etc. I suspect that digital cables pick up EMI and RF to different degrees and therefore induce more or less noise into the analogue parts of any audio system. The reason I think that is that I have done blind tests where me and a couple of buddies have been able to pick which digital cable was which based on how those two same cables sounded when used as analogue interconnects!!! Wierd I know, but some of the characteristics of the cables when used as analogue interconnect cables, could be heard when the same cables were used as digital cables. Therefore the Big Ben, or Benchmark DAC or whatever reclocking you use, does not necessarily mean you do not need to play around with 'flavours' of digital interconnect - and implies some things about use of decent fiber cables instead. |
