Re: [LAU] Audio interface latency measurements

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. 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).

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 :)

--
Len Ovens
www.ovenwerks.net
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