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Old 11th July 2011, 08:41 AM   #1
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Default PC music servers - less jitter

With the PC route, how can jitter be reduced?

Esp as jitter sensitivity increases with higher sample rates . .

I've done some searching, but found nothing conclusive
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Old 16th July 2011, 03:24 AM   #2
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Hi, The switching power supply in a PC has very high EMI noise. So the digital audio signal from it usually comes with very high jitter level, even if you have a good clock osc inside. The best way is replacing the recovered clock with a new low jitter local clock to feed the DAC. I am just cooking a I2S FIFO project new, hopefully there would be some help. Asynchronous I2S FIFO project, an ultimate weapon to fight the jitter
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Old 16th July 2011, 05:43 AM   #3
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Quote:
Originally Posted by iancanada View Post
Hi, The switching power supply in a PC has very high EMI noise. So the digital audio signal from it usually comes with very high jitter level, even if you have a good clock osc inside.
The second sentence does not follow from the first necessarily because the EM noise from the PC's SMPSU generally expresses itself as common-mode noise. It would have to be fairly poor design for the PSU noise to get into the digital signal coming off the motherboard. If this were happening to any degree it would show up on USB interconnects too, giving rise to potential errors as there the bit rate is much faster than with SPDIF.

Jitter gets into SPDIF because every link between transmitter and receiver is necessarily band-limited. This band-limiting causes inter-symbol interference and hence modulation of the transition points from which the clock is inferred by the receiver. Can't be avoided so there's a need for a decent clock recovery circuit to achieve low jitter.
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Old 18th July 2011, 01:16 AM   #4
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Quote:
Originally Posted by abraxalito View Post
The second sentence does not follow from the first necessarily because the EM noise from the PC's SMPSU generally expresses itself as common-mode noise. It would have to be fairly poor design for the PSU noise to get into the digital signal coming off the motherboard. If this were happening to any degree it would show up on USB interconnects too, giving rise to potential errors as there the bit rate is much faster than with SPDIF.
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That's a good point. Jitter sources of a SPDIF stream are very complicated. EMI noise from a switching power supply is only one of them. The most important thing is how to get a good recover clock for the DAC.
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