saam@bigblackbox:/tmp$ jack_control ds alsa dps capture none dps playback none
--- driver select "alsa"
--- driver param set "capture" -> "none"
--- driver param set "playback" -> "none"
saam@bigblackbox:/tmp$ ^C
saam@bigblackbox:/tmp$ jack_control dps capture hw:USB start
--- driver param set "capture" -> "hw:USB"
--- start
DBus exception: org.jackaudio.Error.Generic: Failed to open server
saam@bigblackbox:/tmp$