At Thu, 05 Jun 2008 16:11:49 +0200, Pavel Hofman wrote: > > Hi, > > Please excuse my non-devel question but the most knowledgeable people > read this mailing list. > > Can user-space software (regular players) directly influence quality of > USB adaptive audio output? IOW, how sensitive is adaptive USB to the > rhythm of the data infeed to the USB controller? > > I understand for standard PCI soundcards it is all only about timely > delivery of enough data to DMA memory,the card takes care of the rest > itself. Do USB controllers shield applications from the rest in the same > manner? > > The adaptive mode is sensitive to jitter of the data stream from the USB > controller to the receiver. Can SW players influence the jitter, e.g. by > moving the wav files from HDD to RAM disk etc.? I assume a lightly > loaded system with no major data delays. > > Thanks a lot for any insight, I could not google-out any relevant > information. The usb-audio uses isochronous transport, i.e. you'll send packets of data at a certain period. But, it's a driver implementation issue and from the user-space POV, there is no big difference. The URB-complete callback corresponds to the DMA IRQ of PCI devices. (Of course, if you want a very short period in a real-time manner, the transfer efficiency matters largely, though. But it's a different story than the load you described above.) Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
