Archive for June, 2008

connecting JACK with qjackctl

In my post about the virtual midi keyboard I already mentioned qjackctl, a Qt-based user interface for the JACK demon. It comes with standard packages, my current version is 0.3.2 (website).

qjackctl – main window

qjacktl screenshot

Running the program for the first time, one should set up the demon, since it doesn’t know that it has to use the real-time kernel by default (it didn’t for me). Pressing Setup a window opens up where I enabled the real-time option. I let all other values as they were, Save and OK. Now we are ready to Start the demon. With the Messages button one can see JACK’s information which can be useful when something isn’t working.

Clicking on Connect one can show and hide a window where the internal connections are drawn. Audio and MIDI programs have channels for input and/or output which will show up in this window. After starting the demon with no other (JACK) program running, there are the card’s input and output ports with the name system. I have one each (internal card). One could mark both ports and click Connect and the microphone is wired to the speaker. This is not too exciting but this is a way to go. Better one runs some effect generator like creox which is a simple guitar effects generator (website).  Creox has to be put into play mode either by pressing space or through the Effector menu.

qjackctl – connections window

qjackctl screenshot connections

Using the voice might lead to interesting results. Now I can sing with echo or distortion!

Other features of the user interface will be topic of later posts.

that’s the spirit!

Browsing in the internet looking for blogs connected to this one I stumbled upon a “proof of concept”: ken’s blog! He uses linux audio software (and free samples) to make music and puts it online that one can listen to (and download) it. A variety of programs, a variety of styles. And apparently he does it live as well. Nice one!

a virtual midi keyboard

As I wrote before, I will talk about some different programs I use for audio live performances. After having JACK installed it’s time to start working with it. Most audio programs will have some interface to MIDI signals to give us control over what they are doing. Think of it more like a generic control device than just a piano keyboard, because MIDI signals are used as well to start or stop something, to change effects… You might know that. My point is, that if you don’t have an external MIDI keyboard it comes handy to use the computer’s keyboard. The most basic program which achieves that is vkeybd which is a standard package on debian based linux systems (such as ubuntu). The following picture shows its rather ascetic window: screenshot vkeybd
Three octaves are available, although only one was accessible in my standard installation. I added a few lines in the file ~/.vkeybdmap, which is kind of self explaining, but one has to know how to call those weird keys on localized keyboards (which I don’t). After you start JACK and vkeybd a “readable client” shows up in the connection window’s tab named ALSA (if you use QjackCtl; see picture).
screenshot connection window with vkeybd ports
You can even start up more than one keyboard and its name is given in the command line with vkeybd --name "2nd keyboard". Then one marks the desired ports (in my screenshot no other program is running) and click on connect. Press keys (with focus on vkeybd) and see how they change colors ;). That’s it. Have fun!

Advice: I’m not sure but it could be that libmidisport has to be installed. I’ll find out about that later.