Moving ALSA digital crossover from Volumio 2 to 3

Help and Support
#1

I am using the two channels on my DAC to independently drive the drivers in my speaker through a custom ALSA filter or a digital crossover.

Volumio 3 seems to override the ALSA config file on startup and the only documentation I can find to overcome this is to write a plugin for my ALSA digital crossover.

This is something unique to my installation and I see little value in mastering the Volumio plugin SDK just to get my ALSA filters working again.

Is there a way to include my ALSA snippet into my installation without development?

Thanks!

#2

I’ve tried moving my old ALSA config over to a plugin but the best I can get it to still gives the following error in mpd:

Jul 03 17:09 : client: [0] opened from local
ALSA lib pcm_params.c:2226:(snd1_pcm_hw_refine_slave) Slave PCM not usable
ALSA lib /home/pi/volumio-alsa-plugin/src/pcm_volumioswitch.c:174:(_snd_pcm_volumioswitch_hw_params) PCM volumioMultiRoomServer failed to read the hardware parameters for pcm loki

mpd: pcm.c:710: snd_pcm_name: Assertion `pcm' failed.

My ALSA snippet looks like this:

# SEAS Loki - Start
# Create a plug for the crossover
pcm.loki {
    type plug
    slave {
      pcm "loki-makemono"
      format "unchanged" 
      channels "unchanged"
    }
}


# Digital Crossover for SEAS Loki
pcm.loki-makemono {
    type route
    slave.pcm "loki-filter"
    ttable {
        0.0 1    # in-channel 0, out-channel 0, 100% volume
        1.0 1    # in-channel 1, out-channel 0, 100% volume
    }
}

pcm.loki-filter {
     type ladspa
     slave.pcm "loki-speaker"
     path "/usr/lib/ladspa"
     channels 2
     plugins
     {
          0 {
               label RTlr4lowpass
               policy none
               input.bindings.0 "Input"
               output.bindings.1 "Output"
               input { controls [ 2900 ] }   # low left [ frequency (-6 dB XO point)]
          }
          1 {
               label RTlr4hipass
               policy none
               input.bindings.0 "Input"
               output.bindings.0 "Output"
               input { controls [ 2900 ] }   # high left (match freq above)
          }

     }
}


pcm.loki-speaker {
    type plug
    slave {
     pcm "loki-t-table"
     channels 2
     rate "unchanged"
    }
}

pcm.loki-t-table  {
    type route
    slave.pcm "loki-complete"
    ttable {
      0.0   0.8175
      1.1   1
    }
}


pcm.loki-complete {
  type copy
  slave.pcm "lokiout"
}

# SEAS Loki - End crossover.

Removing pcm.loki-filter from the ALSA chain removes the error but defies the point of the exercise.

Any help would be appreciated.

#3

hello!
not sure to help but to my understanding…
your alsa does :

  • join L and R for mono output
  • send to left freq >2900Hz with an attenuation 0.8175
  • send to right freq <2900Hz
    Am I right?
#4

Hi!

Yes, that is correct.

The tweeter is connected to the left channel and the mid woofer to the right channel on this driver.

Thanks

#5

I understand, but do you know you can achieve this with FusionDsp?

#6

Thank you, I think I got it working (for now, I had to address the hardware directly which is technically not allowed in Volumio plugins).

My implementation: https://github.com/dirkackerman/volumio-plugins-sources