[wdmaudiodev] Where is the latency in the USB audio stack ?
- From: "Jerry Evans" <jerry@xxxxxxxxxx>
- To: <wdmaudiodev@xxxxxxxxxxxxx>
- Date: Mon, 19 Apr 2004 16:13:50 +0100
Hi all.
We have some custom input only hardware running over USB 1 at 6 * 16 * 48K.
Most happily the stock WinXP SP1 USB audio driver works properly when accessed
in KS mode from our own user-mode app(s). The downside of this arrangement is
that we need to sync 2 KS devices to enable low-latency playback. Measurements
indicate that having 2 USB devices plugged into a single USB 2 hub
(theoretically optimal configuration) gives us a minimum practical latency of
~45 ms. This leads me onto the core issue: Given that there is at least 10ms
latency in the USB audio stack (as posted by DJS sometime last year in this
list) we were wondering if a suitable USB driver could be made to supplant the
stock USB stack, i.e. the user could opt to install the high performance
driver. Question is how much of a win we might get: is the latency all in
usbaudio.sys or is it further down the stack ? We'd be most happy if we could
get the overall latency down below 20ms. Any tips would be greatly appreciated.
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