Hello Pierre et al, In the USB Audio driver as it exists in XP you can expect at least a latency of 10 ms by design plus whatever time it takes to do the data copy to the submitted buffers. There are several factors which cause this. 10 milliseconds of data are gathered by the USB Audio driver in a single URB request. When capturing from USB there is no guarantee that the device will completely fill the submitted data buffer for the packet. The URB indicates the amount of data filled in. Thus it is necessary to copy that data from the request to the data buffer submitted by the application instead of filling that buffer directly. It was not an option not to compact the data this way since applications like sndrec32 depended on the data being supplied this way. Granted the choice of 10 milliseconds per request was based on making the math for the driver easier and decreasing IRP overhead. It could likely be trimmed down in future versions, but that is how it works now. DJ Sisolak Microsoft Corp. This posting is provided "AS IS" with no warranties, and confers no rights. -----Original Message----- From: wdmaudiodev-bounce@xxxxxxxxxxxxx [mailto:wdmaudiodev-bounce@xxxxxxxxxxxxx] On Behalf Of Andrew Sherbrooke Sent: Wednesday, June 25, 2003 10:23 AM To: wdmaudiodev@xxxxxxxxxxxxx Subject: [wdmaudiodev] Re: Capture latency with USB card Hi Pierre, >With a USB audio device though, the minimum stable delay I can get is >around 20-25 ms. >The cause of the problem seems to be the instability of the capture side. >I measure the time >between capture events and I get delays up to 20ms on USB where it should >be 5ms. > >I am using Microsoft USB audio driver (latest version) and I heard that >it can achieve better >performance. Did anybody experienced such problems with USB audio? > I had similar experiences. The events I was waiting on were being signaled at such uneven intervals that my latency was fairly unusable - it would tick along regularly for a while (every few ms, corresponding to my buffer size), then I'd suddenly get a delay which was greater by at least a factor of 10. Although this problem seemed to be more significant when I added capture, I don't recall verifying that it was explicitly because of the capture side, as opposed to a result of running capture and render together... Sincerely, Andrew Sherbrooke Art & Logic Lead Engineer, Audio/Media Development asher@xxxxxxxxxxxx www.artlogic.com ****************** WDMAUDIODEV addresses: Post message: mailto:wdmaudiodev@xxxxxxxxxxxxx Subscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=subscribe Unsubscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=unsubscribe Moderator: mailto:wdmaudiodev-moderators@xxxxxxxxxxxxx URL to WDMAUDIODEV page: http://www.wdmaudiodev.de/ ****************** WDMAUDIODEV addresses: Post message: mailto:wdmaudiodev@xxxxxxxxxxxxx Subscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=subscribe Unsubscribe: mailto:wdmaudiodev-request@xxxxxxxxxxxxx?subject=unsubscribe Moderator: mailto:wdmaudiodev-moderators@xxxxxxxxxxxxx URL to WDMAUDIODEV page: http://www.wdmaudiodev.de/