kb

kb is a customizable virtual MIDI keyboard daemon for JACK Audio Connection Kit. It provides MIDI input for standalone JACK synthesizers and can be a useful debugging tool for developing JACK-based audio applications.

Usage

First start a JACK server using jackd(1) or qjackctl(1) (see 1 for details on how to set it up), then run

$ kb

to start the MIDI keyboard daemon. Then, you need to connect the midi_out port of kb to other applications (for qjackctl, use the Graph or Connect button):

+----+-----------+       +-------+-----------+
| kb |           |       | synth |           |
+----+           |       +-------+           |
|                |       |         audio_out +--->
|       midi_out +------>+ midi_in           |
+----------------+       +-------------------+

Alternatively, use the -a option to let kb automatically detect and connect to input MIDI ports:

$ kb -a

kb will capture all the key presses and convert them into MIDI messages according to your configuration.

For the default configuration, the home row of a QWERTY keyboard

ASDFGHJKL;'

corresponds to the white keys on a piano keyboard, and

WETYUOP]

corresponds to the black keys. Additionally, ZX, CV, 90, and -= can be used to decrement and increment octave, velocity, bank, and program, respectively. And the Escape key is the panic button (turn off all notes). You can easily customize these keybindings. See CUSTOMIZE section for details.

If you want to shut down the daemon, press Ctrl-C in the terminal to send a SIGINT signal or run

$ pkill kb

to kill the daemon process. For more information, see kb(1).

Build

First, make sure JACK, Xlib, and libxi are installed. For Arch-based distros, they can be installed by

$ pacman -S jack2 libx11 libxi

For Debian-based distros, install the dependencies by

$ apt-get install libjack-jackd2-dev libx11-dev libxi-dev

If you don't want to use libxi, check out the no_ext branch. The no_ext version works exactly the same, but it might have some issues capturing input within REAPER on Linux.

You also need a C99-compatible C compiler and POSIX make. After all the requirement are satisfied, run

$ make

to build kb and

# make install

to install it to your system.

Customize

kb can be customized by editing the config.h file and recompiling the source code. The default configuration is in config.def.h. It provides a simple one-row keyboard layout. Run

$ make config.h

to obtain the default config file.

Take a look at the alternative layouts in

• config.2row.h: two row keyboard layout (2 octaves)
• config.min.h: the minimal config file

to understand how to customize kb.

FAQ

Can I use kb with ALSA?

Use a2jmidid 2.

How can I add new MIDI messages?

See write_midi in jack.c.

Caveats

1. kb has only been tested on Linux and with JACK 2. It should work on any system with X11 and JACK support, but I have not tested other systems yet. Feedbacks are welcome.
2. Note that kb captures your key presses in any window. It does not intercept them. This is intentional, because I frequently need to edit code while testing the MIDI input. As an additional benefit, you can now enjoy some crappy generative music while typing.