LV2 host for Jack controllable via socket or command line
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mod-host is an LV2 host for JACK, controllable via socket or command line

Currently the host supports the following LV2 features:

  • lv2core
  • atom
  • buf-size
  • event
  • midi
  • options
  • presets
  • time
  • uri-map
  • urid
  • worker

mod-host is part of the MOD project.


mod-host uses a simple Makefile to build the source code. The steps to build and install are:

make install

You can change the base installation path passing PREFIX as argument of make.


libjack-jackd2  >= 1.9.8
liblilv         >= 0.14.2
libreadline     >= 6.2
lilv-utils      (optional)


For developing start it like this:

$ ./mod-host -n -p 5555 -f 5556

mod-host does not startup JACK automatically, so you need to start it before running mod-host.

If you run mod-host without options the process will be forked and it can only be controlled through the socket. The default socket port is 5555, this can be changed by passing the option -p (or --socket-port) to mod-host.

The other way to control mod-host is the interactive mode, in this case the commands must be provided on the shell prompt. The interactive mode has autocomplete, therefore, you can always type [TAB] twice any time you want a hint.

Note: When you are in the interactive mode, socket communication won't work.


-v, --verbose
    verbose messages

-p, --socket-port=<port>
    socket port definition

-f, --feedback-port<port>
    feedback port definition

-i, --interactive
    interactive shell mode

-V, --version
    print program version and exit

-h, --help
    print help and exit

Commands (or Protocol)

The commands supported by mod-host are:

add <lv2_uri> <instance_number>
    * add an LV2 plugin encapsulated as a jack client
    e.g.: add 0
    instance_number must be any value between 0 ~ 9999, inclusively

remove <instance_number>
    * remove an LV2 plugin instance (and also the jack client)
    e.g.: remove 0

preset_load <instance_number> <preset_uri>
    * load a preset state to given effect instance
    e.g.: preset_load 0 ""

preset_save <instance_number> <preset_name> <dir> <file_name>
    * save a preset state from given effect instance
    e.g.: preset_save 0 "My Preset" /home/user/.lv2/my-presets.lv2 mypreset.ttl

preset_show <instance_number> <preset_uri>
    * show the preset information of requested instance / URI
    e.g.: preset_show 0

connect <origin_port> <destination_port>
    * connect two effect audio ports
    e.g.: connect system:capture_1 effect_0:in

disconnect <origin_port> <destination_port>
    * disconnect two effect audio ports
    e.g.: disconnect system:capture_1 effect_0:in

bypass <instance_number> <bypass_value>
    * toggle effect processing
    e.g.: bypass 0 1
    if bypass_value = 1 bypass effect
    if bypass_value = 0 process effect

param_set <instance_number> <param_symbol> <param_value>
    * set a value to given control
    e.g.: param_set 0 gain 2.50

param_get <instance_number> <param_symbol>
    * get the value of the request control
    e.g.: param_get 0 gain

param_monitor <instance_number> <param_symbol> <cond_op> <value>
    * do monitoring a effect instance control port according given condition
    e.g: param_monitor 0 gain > 2.50

licensee <instance_number>
    * get the licensee name for a commercial plugin
    e.g.: licensee 0

monitor <addr> <port> <status>
    * open a socket port to monitoring parameters
    e.g: monitor localhost 12345 1
    if status = 1 start monitoring
    if status = 0 stop monitoring

monitor_output <instance_number> <param_symbol>
    * request monitoring of an output control port in the feedback port
    e.g.: monitor_output 0 meter

midi_learn <instance_number> <param_symbol> <minimum> <maximum>
    * start MIDI learn for a parameter
    e.g.: midi_learn 0 gain 0.0 1.0

midi_map <instance_number> <param_symbol> <midi_channel> <midi_cc> <minimum> <maximum>
    * map a MIDI controller to a parameter
    e.g.: midi_map 0 gain 0 7 0.0 1.0

midi_unmap <instance_number> <param_symbol>
    * unmap the MIDI controller from a parameter
    e.g.: unmap 0 gain

midi_program_listen <enable> <midi_channel>
    * listen for MIDI program messages for the specified midi channel in the feedback port
    e.g.: midi_program_listen 1 0

cc_map <instance_number> <param_symbol> <device_id> <actuator_id> <label> <value> <minimum> <maximum> <steps> <unit> <scalepoints_count> <scalepoints...>
    * map a Control Chain actuator to a parameter
    e.g.: midi_map 0 gain 0 1 "Gain" 0.0 -24.0 3.0 33 "dB" 0

cc_unmap <instance_number> <param_symbol>
    * unmap the Control Chain actuator from a parameter
    e.g.: unmap 0 gain

    * return current jack cpu load

load <file_name>
    * load a history command file
    * dummy way to save/load workspace state
    e.g.: load my_setup

save <file_name>
    * saves the history of typed commands
    * dummy way to save/load workspace state
    e.g.: save my_setup

bundle_add <bundle_path>
    * add a bundle to the running lv2 world
    e.g.: bundle_add /path/to/bundle.lv2

bundle_remove <bundle_path>
    * remove a bundle from the running lv2 world
    e.g.: bundle_remove /path/to/bundle.lv2

feature_enable <feature> <enable>
    * enable or disable a feature
    e.g.: feature_enable link 1
    current features are "link" and "processing"

transport <rolling> <beats_per_bar> <beats_per_minute>
    * change the current transport state
    e.g.: transport 1 4 120

    * report feedback port ready for more messages

    * show a help message


For each effect added one client on JACK will be created. The names of clients follow the standard: effect_<instance_number>

If a valid command is executed a response is given as following:

resp <status> [value]

If status is a negative number an error has occurred. The table below shows the number of each error.

status error

A status zero or positive means that the command was executed successfully. In case of the add command, the status returned is the instance number. The value field currently only exists for the param_get command.