Version 0.1
Removes crackles provoked by signal spikes, for example snare overloads, by selectively applying a low-pass filter to half-waves reaching a given treshold using a convolution matrix - leaving other parts untouched. This audio plugin can be used with any LADSPA host, such as Audacity.
No miracle here. If a long period of audio signal is saturated, it will always sound saturated. "Mechanical" saturation, coming from the microphone itself, is another problem which usually cannot be solved by this plugin, because the perturbation frequency range is too wide. However, the crackles and pops created by digital spikes, which are actually high-level harmonics due to brutally plateauing waves, will locally disappear, leaving a (hopefully) more audible track.
Values for the treshold and the convolution matrix have been chosen by ear. If you feel you have better ideas (and you can hear the difference), or if the plugin doesn't work as it should, just send me an email.
Additionally, this plugin also works as a very simple compressor on clean tracks. Random peaks often happen on live recordings, without any real relation to music dynamics. These peaks impair a straightforward normalization at 0dB, and sometimes you have to manually attenuate them one by one. Running the Despiker plugin will level these unwanted spikes, usually giving the ability to amplify the whole track by at least 1dB. Repeating the process more than twice is not recommended since the low-pass filter would affect a lot more half-waves, losing more information than necessary. If you want to really compress the signal, use a real compressor.
Copyright (C) Jean Zundel jzu@free.fr 2012
Free software, licensed under the GNU GPL v3.
The ladspa.h file, included in this project, comes from the ladspa-sdk package
and allows to compile the plugin without installing the whole package. Type:
make
sudo make install
That's about it. You can now use the plugin.
Once the despiker_4741.so library has been copied to /usr/lib/ladspa/,
enter Audacity and load a problematic audio track. Go to
Effects > Modules... > Despiker.
Done.