GoodSoundClub - Romy the Cat's Audio Site

In the Forum: Didital Things
In the Thread: High Quality Music Server / CD player

Post Subject: Timing is everythingPosted by jessie.dazzle on: 12/11/2008

Romy wrote :

"...The USB is full duplex or bi-directional interface where stream flows in both ends. This enables designers to put a clock that might everything on the receiver side (DAC) and let this clock to manage the USB’s and even reader timing. USB sends data in burps by requests of by scheduled timing, this marks all might be managed by receiver side clock. In ASE/EDU the receiver shell recognize the timing marks and PLL or re-clock data. In USB there are no needs for PLL or re-clocking as the data arrives at the marks of the original clock. The USB in this case acts like an elephant that sticks a long trunk to another devise and sucks juice… according to my consultants this USB implementation is the most proper way to do the things..."

This is the point I was trying to make in the following post
http://www.goodsoundclub.com/GetPost.aspx?PostID=8293&Phrase=
where I quoted the manufacturer of a USB DAC reproducing the following information:

"...The USB interface is bidirectional, and has built-in error correction and buffering at both ends; it is an asynchronous interface. Clocking synch problems associated with SPDIF are not present with USB. The result is that the data on the disk is identical to what is leaving the DAC all the time...At start-up, the DAC tells the computer it can handle 16 bit audio at 32K, 44.1K and 48K. Since the USB receiver only has to handle these 3 frequencies, the clocking to the DAC has almost no jitter. SPDIF actually has to be synched to the exact frequency of the transport (i.e. if the transport is working at say 44.0896K instead of 44.1K the DAC has to sync to that frequency). Therefore the jitter problems of SPDIF are all but eliminated. The result is a zero error protocol to link between computer and DAC, with ultra low jitter... I wrote that there is no filtering : However, this unit uses a tube in it's output stage ("...Once converted, the analog signal is sent directly to a 6GM8/ECC86 dual triode output tube, which in turn drives a pair of output transformers..."); the tube probably has some sort of filter-like effect..."

Those considering a USB DAC may want to read my impressions in the above-linked post.

jd*

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