Version 1.0
Real-time audio processing
Copyright (C) Jean Zundel jzu@free.fr 2010
slab is an evolutive guitar effect designed for the Linksys NSLU2 running GNU/Linux, but it works on any ALSA-based architecture. It is licensed under the GNU GPL v3.
Just type make and you're done. You'll need libasound2 and libpthread
libraries (+devel), and gcc.
Running it as root allows to use the Slug's LEDs.
This program needs an USB joystick - or something similar, like a converted wah
controller - to operate. It currently manages two potentiometers and four
switches, but there's room for easy expansion. You will need to tinker with
#defines to map the physical controls with the desired effects.
The -d option ouputs debug messages (ALSA errors and joystick events).
Once you're all set, you want to edit /etc/inittab to insert this line:
sl:23:respawn:/[PATH_TO]/slab
(obviously replacing [PATH_TO] with its actual path)
which will ensure that init(8) restarts the program when it is stopped.
telinit q will re-read the inittab file.
Mounting the / filesystem read-only prevents data corruption, but you have to
create ramdisks for /tmp and /var/run directories in /etc/fstab.
/dev/sda2 / ext3 ro 0 0
(...)
none /tmp ramfs size=512k 0 0
none /var/run ramfs size=512k 0 0
Activating eth0 mysteriously fails with readonly filesystems, so
this kludge in /etc/rc.local temporarily switches to rw,
ifconfigs eth0, then switches back to ro.
mount /dev/sda2 / -o rw,remount
ifconfig eth0 192.168.0.106
sleep 1 # Yes, you really need it. Whatever.
mount /dev/sda2 / -o ro,remount
Enormous hiss! The el-cheapo USB soundcard I used for my tests is to blame. The "noise gate" effect helps only to a point.
When the program starts, it doesn't know the position of pots, since they cannot be read: events are pushed from the controller to the computer. Since this kind of device is seldom restarted during a session, this behaviour is minor, but sometimes surprising.
Any external process/event affects ALSA management and creates an
unwanted delay. You have to stop the program, which will be restarted
by init if /etc/inittab is set up accordingly.
Hence, Debian is perfect for programming/compiling/debugging, but a stripped-down distro might be more adequate for everyday use. See OpenEmbedded (http://wiki.openembedded.net/) and others.