On 06/21/2014 07:18 PM, Len Ovens wrote: > On Sat, 21 Jun 2014, Robert Jonsson wrote: > >> Follow up question: from a theoretical perspective, is it likely a usb >> 2.0 interface would have similar transport latency as firewire? Usb 1 >> I suppose would be worse due to lower clockspeed. > > As was already stated, clock speed of the interface is not really > relevant. It seems in fact that no one is really interested in USB3 > because it does not have any improvement for audio, USB2 is enough. The > limitation with USB1 is bit depth, bit rate and channel count. > > In general, throughput and latency are two different things. Larger > packets mean better throughput, but smaller packets mean lower latency. > > I am not sure, but it seems to me the USB1.1 audio standard effectively > means that the lowest latency for USB1 is jackd set to 64/2. With my Edirol UA-25 lowest possible setting is 48/2 @ 48kHz. This is the > smallest buffer size supported. I do not know, but it seems that fire > wire audio is about the same from what I have read (I don't have one of > my own to confirm). With the FireWire interfaces I've owned I could go as low as 16/3 @ 48kHz. But settings like this are unusable, DSP load qickly rises as soon as you start doing something serious. Nice to brag about but that's about it ;) > > The main trouble with USB is on the MB. Finding a USB port that is not > shared with something else via an internal hub. I think adding a USB > card would make things better, but trying different ports on a laptop > gives good results too. With any audio interface, having it's own irq is > important, I have moved PCI cards to different slots with a big > difference. It shouldn't be, but it seems tunning a computer for audio > is a must still for low latency. Audio is very definately _not_ plug and > play for (semi)pro audio work. There is no silver bullet kernel or > distro that just makes everything work. On my laptop, there is one USB > port that gives good audio... so long as the port next to it is empty... > and the wireless kernel module is unloaded and .... you get the picture :) > It's indeed a matter of finding a free USB port. If you don't have any you have to resort to unloading kernel modules or even unbinding drivers. Jeremy > -- > Len Ovens > www.ovenwerks.net > > _______________________________________________ > Linux-audio-user mailing list > Linux-audio-user@xxxxxxxxxxxxxxxxxxxx > http://lists.linuxaudio.org/listinfo/linux-audio-user
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