Subject: RE: [linux-audio-user] USB Quattro and Jack questions
From: Mark Knecht (mknecht_AT_controlnet.com)
Date: Tue May 27 2003 - 21:30:32 EEST
>
> Another thing about the quattro is that even the windows drivers will
> not allow you to record and playback on all 4 channels at one time.
>
> You can use
>
> 4 in, 2 out 48khz 24 bit
> 2 in, 4 out
> 2 in, 2 out 94 khz 24 bit
>
> I think I am running up against this with my latest attempts. It may be
> that the quattro cannot do all 8 channels because of a hardware switch
> maybe for power consumption or something. They do run awfully hot and I
> can imagine that it would be possible to melt something if their is too
> much power running through them.
>
USB 1.0/1.1 is built on a 12Mb/Sec physical layer.
96000 * 24-bits * 4-channels = 9.216Mb/S if I did the calculations
correctly.
I think that's probably more than USB can really handle. When I worked for a
company that did USB hardware, we found in many PCs (at that time -
1996-1999) that most USB implementations would really do much more than
about 2Mb/Sec reliably. The newer implementations are much better, but these
numbers bring you up to 75% bus efficiency. Even 1394 doesn't get much
beyond that and it uses much larger packet sizes to get some of that.
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