[linux-audio-user] USB Quattro and Jack questions

[Patrick Shirkey]

Mark Knecht wrote:
>>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.

that should be divided by three to get bytes as there are 8 bits in 
every byte the quattro uses 24 with 3 periods (not packed in four like 
other cards).

24 * 3 bytes * 48000 =  3072000 bytes
=> 3072 Kb
=> 3.072 Mb/S

> 
> 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.
> 

That comes as no surprise to me that the usb protocol cannot handle 
effectively it's full bandwidth.

But it should be easily able to handle this:

44100 * 2 bytes * 8 channels (4 in, 4 out) = 705600 bytes
=> 705.6 Kb/S



-- 
Patrick Shirkey - Boost Hardware Ltd.
Http://www.boosthardware.com
Http://www.djcj.org - The Linux Audio Users guide
========================================

Being on stage with the band in front of crowds shouting, "Get off! No! 
We want normal music!", I think that was more like acting than anything 
I've ever done.

Goldie, 8 Nov, 2002
The Scotsman