Christian Pernegger wrote:
[healthy skepticism snipped]
Either the bit stream is tranmitted intact or it is not. There is no in-between. Sure, the waveform is distorted but there would have to be in insane lot of this "line induced jitter" to actually flip bits.
You're missing the point completely. It's not as simple as "the bitstream is transmitted intect or it is not". At the implementation level, this "bitstream" is actually a sequence of precisely-timed voltage transitions. This stream is decoded by the DAC to produce the analogue waveform. If the timing of those transitions is slightly out then the analogue waveform is distorted.
Everything else can be fixed by reclocking and hinges on the quality of the reclocking.
Ah, but who said anything about re-clocking? Not all DACs do re-clocking. Those that do it well are not cheap. For example: http://www.av123.com/products_product.php?section=processors&product=1.1
The rest of the article is about recording, which is, espacially with multiple sources, a whole different thing.
Last not least, from that very site:
QUOTE Dual stage Clock recovery can also be combined with a data buffer memory.
The first PLL writes to the buffer, and the second PLL reads from the buffer and tries to keep it always half filled.
If we use a FIFO (first in first out) memory as a data buffer, we have more time to react to clock variations of the input signal and thus are able to attenuate lower jitter frequencies. The larger the buffer, the lower the jitter frequency that can be attenuated.
The disadvantage of the FIFO memory solution is (beside its higher price) that the output data will be delayed (the buffer has to be half filled before data is output).
UNQUOTE
Higher price: What higher price? $150 would buffer you a CD. Even SRAM is not prohibitively expensive. It's true that buffers delay the output but they shift it CONSTANTLY meaning you don't want to use this technique for recording but for playback it's just fine.
Show me scientific proof that using the above quoted jitter reduction method directly before the DAC (on the same circuit board) the jitter at the DACs output is influenced by the jitter at the input. Till then I suggest reading up on "placebo" :)
I'm not sure what point you're making here. You seem to be saying that you agree that jitter exists as a problem and are presenting several mechanisms to reduce it.
I never said that jitter is *always* a problem, merely that in low-budget equipment it often is. Consumer audio equipment is designed to a budget - there's no other reason that all CD players don't produce audiophile quality output.
You still seem to be confused.
R. -- http://robinbowes.com
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