On Sun, Dec 30, 2012 at 02:22:51PM +0000, Ben Bell wrote:

> Running with a more modest session hovering at 30% normally, pulling the
> alsa_in channels (just into jack -- no connections) raises the CPU to ~55%
> but there are no xruns.
>
> So it seems that the problem is most likely in the alsa multi plugin. As an
> aside I'm surprised at the extent of resource usage caused by simply having
> alsa_in running. Normal, or suspicious? jack_netsource doesn't cause this
> sort of load, and tweaking sample rate and the like doesn't seem to affect
> things. A side-effect of it expecting to need to resample everything?

You could try zita-a2j instead of alsa-in. On my old 2G P4 machine
adding 8 channels that way takes 10% CPU. Sound quality is vastly
better than alsa-in.