[LAD] JACK on Gigaport HD+ at 4800kHz (reduced channel count)

Clemens Ladisch clemens at ladisch.de
Tue Feb 25 15:00:30 UTC 2014

Fons Adriaensen wrote:
> On Tue, Feb 25, 2014 at 08:39:14AM -0500, Paul Davis wrote:
>> imagine you have an N (where N > 16) channel device but only channels 1-4
>> are connected. the channel count option stops you from having to look at
>> N-4 useless channels on the device all the time.
> AFAIK, when using the MMAP access mode, you always get the full channel
> count.

Regardless of the access mode, you can get as many channels as the
hardware supports.  Typically, consumer hardware supports 2/4/6/8
channels, while most pro chips don't bother to be flexible.

> For a USB device it will be some kernel memory that gets mapped of course,
> so in theory a selection of channels could be done while defining that
> buffer. But it doesn't seem to work that way.

For USB devices, the number of channels is selected before the buffers
are allocated.  The only constraint is that the device must actually
support that number of channels.

I don't know what the Gigaport actually supports.


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