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synchronous and asynchronous USB Data transfer mode and the Optical out on USB sound Cards

post #1 of 3
Thread Starter 

A USB sound card uses the synchronous mode for data transfer which means the signal will have high jitter, then if we use the optical out on the USB Sound Card, does that mean the signal outputted from the optical port will have high jitter as well ?

 

Equivalently,

 

A USB sound card uses the asynchronous mode for data transfer which means the signal will have low jitter, then if we use the optical out on the USB Sound Card, does that mean the signal outputted from the optical port will have low jitter as well ?

 

in other words after the signal is received through the USB and processed by the DSP and outputted through the optical out, whether it has low jitter/high jitter depends on whether the data transfer mode is asynchronous/synchronous.

 

Can someone confirm this ....

post #2 of 3
Quote:
Originally Posted by Sam21 View Post
 

A USB sound card uses the synchronous mode for data transfer which means the signal will have high jitter, then if we use the optical out on the USB Sound Card, does that mean the signal outputted from the optical port will have high jitter as well ?

 

Synchronous mode is almost never used. Adaptive is more common. Jitter level in the USB soundcard will depend on the quality of the USB receiver. It could be quite (sufficiently) low. This jitter level will directly influence the optical output. The receiver could be followed by an ASRC or another jitter cleaning mechanism. In which case, the jitter in the soundcard will mostly depends on the quality of the local clock.

 

Quote:
 A USB sound card uses the asynchronous mode for data transfer which means the signal will have low jitter, then if we use the optical out on the USB Sound Card, does that mean the signal outputted from the optical port will have low jitter as well ?

 

Only if the local clock inside the USB soundcard has also low jitter.

 

 

In both case, the quality of the optical output and its jitter level will be heavily dependant on how good the spdif output chipset is, on how well clock lines are layed out, on how good the power supply is, etc. The USB protocol is only a small part of the problem.

post #3 of 3
Thread Starter 

thanks for the response

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