Steve Harris wrote: > On Tue, Dec 09, 2003 at 09:25:42AM +0100, Clemens Ladisch wrote: > > > Isoch - 1394 has a timer operating on the bus. This timer happens > > > (roughly) every 125uS. > > > > USB isochronous transfers happen once per millisecond. > > OK, so its the difference between 44 or 45 samples per packet at 44.1kHz > (USB) and 5 or 6 (1394). > > So, a plausible jack period of 64 samples will be 11 or 12 1395 packets, > but always 125uS of jitter of course, (10 or 11 packets at 48k). > > I dont really have any idea how bad that is, its 8% of the availble time > slot for processing the 64 samples. Both USB and 1394 transfer the data in packets (and the packet could arrive near the end of a frame), so it must be buffered in the device anyway. Consequently, this jitter does not appear in the data fed to the DAC. This additional buffering introduces another latency (of ca. one frame), though. Regards, Clemens
