Takashi Iwai napsal(a): > 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, Thanks a lot for your reply which has narrowed down the area I will have to look at detail. Regards, Pavel. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
