Re: [LAU] jdelay - measured latency of a usb interface

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To: <linux-audio-user@...>
Date: Wednesday, April 1, 2009 - 9:47 am

Ken Restivo wrote:

Well, I was simplifying somewhat. In the context of that mail, the
40 ms latency was not the responsibility of the USB device, so
switching to another one would not help.

When using the same sample rate and the same buffer/period settings,
that data that the USB audio driver sends always uses the same timing,
regardless of which device is used.

> > I know, that the manufacturers of USB cards like to brag with their hardware

These differences do exist, but mostly because of differences in
the (Windows) drivers.

> Is it possible that the USB protocol sets a *minimum* on latency,

Yes. The theoretical minimum latency is at least two or three
milliseconds (depending on which assumptions you make); the additional
latency introduced by the DAC itself is much lower than that.
(With kernel 2.6.31 or so, the protocol-related latency of high-speed
(USB 2.0) audio devices can be reduced to one eighth in some cases.)

It is, of course, possible to have additional latency due to DSP
processing or something like that, but nowadays, these things are done
in software.

Best regards,
Clemens
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Messages in current thread:
Re: [LAU] jdelay - measured latency of a usb interface, Frank Barknecht, (Tue Mar 24, 11:32 am)
Re: [LAU] jdelay - measured latency of a usb interface, Arnold Krille, (Tue Mar 24, 12:03 pm)
Re: [LAU] jdelay - measured latency of a usb interface, Frank Barknecht, (Tue Mar 24, 12:18 pm)
Re: [LAU] jdelay - measured latency of a usb interface, Arnold Krille, (Tue Mar 24, 1:21 pm)
Re: [LAU] jdelay - measured latency of a usb interface, Frank Barknecht, (Tue Mar 24, 7:49 pm)
Re: [LAU] jdelay - measured latency of a usb interface, Ken Restivo, (Wed Mar 25, 6:39 am)
Re: [LAU] jdelay - measured latency of a usb interface, Clemens Ladisch, (Wed Apr 1, 9:47 am)
Re: [LAU] jdelay - measured latency of a usb interface, Justin Smith, (Wed Apr 1, 2:08 pm)
Re: [LAU] jdelay - measured latency of a usb interface, Frank Barknecht, (Wed Mar 25, 8:38 am)
Re: [LAU] jdelay - measured latency of a usb interface, James Cameron, (Wed Mar 25, 8:06 am)
Re: [LAU] jdelay - measured latency of a usb interface, Frank Barknecht, (Tue Mar 24, 8:48 pm)