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In Reply to: Yep, and.... posted by pburant on October 20, 2004 at 12:37:11:
Pete,That was interesting to know, thanks. I still fail to understand that given the notion, a bit is a bit, how can the bits be altered by jitters etc. For example, if I copy a MS Windows operating disk using one of the disk burning software such as Disk Juggard etc, the pirated version installed perfectly. Why is it that the music CDR sounded so poorly (I know I'm going around in circles). You mentioned that for a CDP, it's much more important how precisely those bits are layed down, so I interpret that the bit position in the original cd can be altered, is that right?
On the other hand, if I copy a VCD, it will not look much different from the stock version (why isn't the position of the bits altered here?). Why is it only in audio but not video? Interesting topic anyway.
Follow Ups:
Posts: 17mhafner,
My understanding is this; even though a CD is "digital", an audio system is still an analog system. A CD stores "data" by burning pits into a piece of plastic...how deep and how long those pits are need to be within certain tolerances in order for the data to be read correctly, but they still can vary. For the purposes of calculation and math, this data can be manipulated without error. However, you are still dealing with analog voltages whose level and duration are determined by the length and depth of those pits on the CD. Ultimately, the voltages are converted to other voltages at the DAC via a series of resistors and transistors in the DAC...this is an analog process, and the level and duration of the input voltages makes an impact. If those levels and durations (eg. pit depth and length) were not precise, then they will be detrimental to the sound quality produced. In other words, jitter can be stored into the data stream on the CD. In this case, the CDR burner is probably not very precise, so you are hearing the jitter effects...
nt
.
With the MS Windows bits, your compouter can retry time after time to read all the bits until it reads them all. It must get them all in the right order, but this is all independent of time. With a CDP, it can't retry forever, since it's working in real time. Yes, there is oversampling, but in order to continue to reproduce music without interruption, the player must eventually make a decision. Probably a bigger factor than this, however, is that when a CDP does have to sturggle to read a bit properly, this wreaks havoc on the power supply, which can degrade the performance of the DAC, or in the case of a transport only, introduce jitter into the bitstream output.If you visit Jon Risch's web site (there is a link to it in the Asylum FAQs), he goes into much more detail than this. Even though it may be more detail than you want, I'd still recommend it to make sure I haven't passed any of it on incorrectly. The short of it, though, is that the more perfectly the bits are laid down on the disc, the easier it is for your player to properly turn it into music, as the side effects of slobby bits are degraded sound quality.
The bit position on a disc can only be altered via imperfections in the burning process (remember - all things mechanical have tolerances). Moving a bit in any other way would really be changing it from a one to a zero, or vice-versa and therefore altering the content, not just the precision of the digital copy of the content.
As for why you didn't see any differences in the VCD copy, were you using the same player? Even if you were, the video reproduction circuitry may not be as susceptible to jitter as the audio section. There's also the issue of whether or not your eyes are as sensitive to a certain level of jitter on a particular screen as your ears are thru a particular system. If you were to take your original and CDR audio CDs and play tem on a different system, it's possible that you may not hear as much, or any, difference.
-Pete
-Pete
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