Subject: Re: [linux-audio-user] USB Quattro and Jack questions
From: Patrick Shirkey (pshirkey_AT_boosthardware.com)
Date: Tue May 27 2003 - 22:41:01 EEST
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
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