There are lot of existing LADSPA plugins which could be easily used out of the box together with ALSA and kodi. Unfortunately kodi does not support selecting custom ALSA entries. Here is what you need to setup to make it work.

ALSA comes with LADSPA plugin support. A common pattern is to overwrite the default ALSA device with your own including LADSPA. Unfortunately kodi does filter all ALSA devices except the ones directly bound to hardware.

To use LADSPA / ALSA together with kodi, we will have to

• disable pulsaudio
• configure the LADSPA plugin at ALSA
• disable the device filter at kodi sources and recompile it
• create a custom desktop session to use our self-compiled kodi

grep autospawn /etc/pulse/client.conf
autospawn = no

• Here I use my own LADSPA plugin rms_leveler_3s, see https://launchpad.net/~mc-1/+archive/ubuntu/audio-tools , you could use any other plugin here

/etc/asound.conf

#--------------------------------------------------
# Cards
#--------------------------------------------------
pcm.audiophile {
    type hw
    card 1
    device 0
    subdevice 0
}

ctl.audiophile {
    type hw
    card 1
    device 0
    subdevice 0
}

#--------------------------------------------------
# Normal alsa
#--------------------------------------------------
pcm.!default {
    type plug
    slave.pcm "duplex"
} 

pcm.duplex {
    type asym
    playback.pcm "ladspa"
    capture.pcm "dsnooper"
}

pcm.leveler {
    type plug
    slave.pcm "ladspa"
}

# --- ladspa chain ---

pcm.ladspa {
  type ladspa
  slave.pcm "dmixplug"
  path "/usr/lib/ladspa";
  plugins [
    {
        label "rms_leveler_3s"
    }
  ]
}

pcm.dmixplug {
  type plug
  slave.pcm "dmixer"
}


pcm.dmixer {
    type dmix
    ipc_key 1234
    slave {
        pcm "audiophile"
        period_size 1024
        buffer_size 4096
        rate 44100
    }
} 


pcm.dsnooper {
    type dsnoop
    ipc_key 2048
    ipc_perm 0666 
    slave.pcm "audiophile"
    slave 
    {
        period_time 0
        period_size 1024
        buffer_size 4096
        rate 44100
    }
    bindings {
        0 0
        1 1
    }
}

#--------------------------------------------------
# special entries for pulseaudio/apulse
#--------------------------------------------------

pcm.duplexPulse {
    type asym
    playback.pcm "dmixerPulse"
    capture.pcm "dsnooper"
}

pcm.dmixerPulse {
    type dmix
    ipc_key 1234
    slave {
        pcm "audiophile"
        period_size 1024
        buffer_size 4096
        rate 44100
    }
} 

cat /usr/share/xsessions/kodi.desktop

[Desktop Entry]
Name=Kodi
Comment=This session will start Kodi media center
Exec=/home/milan/startKodi.sh
TryExec=/home/milan/startKodi.sh
Type=Application

• disable pulseaudio
• set LADSPA path

startKodi.sh

#!/bin/sh

export LADSPA_PATH=/usr/lib/ladspa
export AE_SINK=ALSA
# kodi-standalone
# /usr/local/bin/kodi-standalone
/usr/local/bin/kodi

• enable use of LADSPA plugins via ALSA
• see https://kodi.wiki/view/HOW-TO:Compile_Kodi_for_Ubuntu

git clone git://github.com/xbmc/xbmc.git xbmc
vim xbmc/cores/AudioEngine/Sinks/AESinkALSA.cpp
 
diff --git a/xbmc/cores/AudioEngine/Sinks/AESinkALSA.cpp b/xbmc/cores/AudioEngine/Sinks/AESinkALSA.cpp
index 4d87afa..8d9f80a 100644
--- a/xbmc/cores/AudioEngine/Sinks/AESinkALSA.cpp
+++ b/xbmc/cores/AudioEngine/Sinks/AESinkALSA.cpp
@@ -48,7 +48,8 @@
 
 #define ALSA_CHMAP_KERNEL_BLACKLIST
 
-#define ALSA_OPTIONS (SND_PCM_NO_AUTO_FORMAT | SND_PCM_NO_AUTO_CHANNELS | SND_PCM_NO_AUTO_RESAMPLE)
+#define ALSA_OPTIONS (SND_PCM_NO_AUTO_CHANNELS)
+
 
 #define ALSA_MAX_CHANNELS 16
 static enum AEChannel LegacyALSAChannelMap[ALSA_MAX_CHANNELS + 1] = {
@@ -1193,17 +1194,7 @@ void CAESinkALSA::EnumerateDevicesEx(AEDeviceInfoList &list, bool force)
        * found by the enumeration process. Skip them as well ("hw", "dmix",
        * "plughw", "dsnoop"). */
 
-      else if (baseName != "default"
-            && baseName != "sysdefault"
-            && baseName != "surround40"
-            && baseName != "surround41"
-            && baseName != "surround50"
-            && baseName != "surround51"
-            && baseName != "surround71"
-            && baseName != "hw"
-            && baseName != "dmix"
-            && baseName != "plughw"
-            && baseName != "dsnoop")
+      else
       {
         EnumerateDevice(list, name, desc ? desc : name, config);
       }

bootstrap
configure
make
make install

• select kodi session on login, at kodi
• select either default or „leveler“ from list of devices at system / audio / source