opaqueice;147542 Wrote: > Sorry, I don't understand what you're saying. I thought cliveb's point > was the following: > > the bits recorded on a CD bear little resemblance to the bits in the > S/PDIF stream, because of interleaving and error-checking codes. > > Therefore, the bits must first be read into a buffer, after which they > are processed by some chip which decodes them to S/PDIF and sends them > to a DAC chip or a digital out. > > Now, the point was that, since the bits are coming from a buffer and > not directly from the CD, there is no real difference between a CD > player and a solid state player like the SB. Of course there can be > some jitter going into the DAC, or in the DAC clock itself, but that's > got nothing to do with the CD (modulo some form of electrical > interference caused by the moving parts). > > You're saying that the same oscillator controls the speed of the CD > spinning and the DAC, but.... so what? That doesn't seem to > invalidate his point at all.
My point is that the buffer that is doing the decoding of the bits on the disk is clocked by the PLL clock that is influenced by the jitter on the disk. The clock that clocks the buffer input is identical to the clock that clocks the buffers output. It is one PLL clock and it gets jittery from the variable spacing of the bits on the disk. This buffer is only a holding place in order to decode the bits. It is NOT an elastic buffer for reclocking the bits. There is only one PLL that locks to the bit-stream. If the frequency of this clock varies much from the bitstream frequency, there would have to be a very large buffer to take up these short-term frequency differences to prevent overrun or underrun. Therefore, the PLL frequency must track the bit frequency quite closely. No matter how you look at it, if there is one PLL and it must track the bit-rate coming off the disk, then it will be affected to some extent by the jitter in the pits and motor speed-variation, loop-control, mechanical resonance of the disk spinning etc... Unless you can completely decouple the disk bitstream from the clock that clocks-out the S/PDIF data stream, there will always be jitter in the output signal due to the disk and its mechanical/electrical systems. The players that eliminate this read from the disk at high speed into an elastic buffer. Then it is basically a read from RAM. Both shock-proof portables and computer-based units can do this. Steve N. Empirical Audio -- audioengr ------------------------------------------------------------------------ audioengr's Profile: http://forums.slimdevices.com/member.php?userid=8041 View this thread: http://forums.slimdevices.com/showthread.php?t=28621 _______________________________________________ audiophiles mailing list [email protected] http://lists.slimdevices.com/lists/listinfo/audiophiles
