1pcm.!default {
2    type plug       # <-- no { here
3    slave.pcm {
4        type multi
5        slaves {
6            a { channels 2 pcm "hw:0,0" }  # the real device
7            b { channels 2 pcm "hw:Loopback,0" }  # the loopback driver
8        }
9        bindings {
10            0 { slave a channel 0 }
11            1 { slave a channel 1 }
12            2 { slave b channel 0 }
13            3 { slave b channel 1 }
14        }
15    }
16    ttable [
17        [ 1 0 1 0 ]   # left  -> a.left,  b.left
18        [ 0 1 0 1 ]   # right -> a.right, b.right
19    ]
20}
21