22 Dec
2009
22 Dec
'09
4:12 a.m.
On 12/22/2009 05:47 PM, Ng Oon-Ee wrote:
On Tue, 2009-12-22 at 15:44 +1100, Patrick Shirkey
wrote:
Normally, period sizes as you describe above are the right way to go but
with usb devices the packet sizes are different to pci cards so you will
see better performance with these strange period sizes. That's not to
say the card won't work it's just that you will be transferring more
packets with period sizes that are not exact multiples of the frame rate
and putting the system under more stress.
At least that's what I understand from Takashi Iwai who wrote the first
version of the alsa usb driver.
I have personally found that with a fast enough cpu and plenty of memory
that I can run a usb-1.0 device at 64 periods and 44100 frame rate with
-n3 and get 4 channels of i/o.
Cheers.
Patrick Shirkey
Boost Hardware Ltd
Are you running the usb device at 44100 or 48000?
Ideally usb cards
should be run at 48000 with period sizes that divide perfectly into
48000. i.e 100, 200, 400, etc...
Could I know more about this, please? 48000 would be the
'generally'
used (besides 96k) for USB sound cards I understand, but what's this
about period sizes? I've always thought period sizes were of the series
8, 16, 32, 64, 128, 256...