Playback through softvol locks mixer

[Martin Bailey <martin@pcalpha.com>]

Hi,

I setup an ALSA plugin chain to allow individual volume-controlled mono 
access to a 4-channel sound card. I'm including the asound.conf only for 
the first channel. Whenever I open "plug:playback1" and play audio, it 
appears the "playback1" softvol mixer goes locked and any attempt to 
change its value within the same or another application results in 
"Operation not permitted". Can you think of something I might be missing?

pcm.playback8k {
         type dmix
         ipc_key 666
         ipc_perm 0666
         slave {
                 pcm "hw:0"
                 format S16_LE
                 channels 4
                 rate 8000
                 buffer_size 8192
                 period_size 1024
         }
         bindings.0 0
         bindings.1 1
         bindings.2 2
         bindings.3 3
}

pcm.playback8k1 {
         type route
         slave {
                 pcm "playback8k"
                 format S16_LE
                 channels 4
         }
         ttable.0.0 1
}

pcm.playback1 {
         type softvol
         slave.pcm "playback8k1"
         control.name "playback1"
         control.card 0
         control.count 1
         min_dB -51.0
         max_dB 0.0
         resolution 256
}
ctl.playback1 {
         type hw
         card 0
}