Version 0.666
Satana (Saturation Analogique) is a LADSPA plugin which can be used with any compatible host, such as Audacity, MPlayer, or Ardour(¹). It tries hard to simulate an analogue saturation device, like a magnetic tape recorder whose VU meters are stuck in the red, or a tube amplifier's push-pull stage. In my opinion, it fails, but musicians may nonetheless find the resulting effect interesting.
It begins with an optional compressor, which does the evil part, then applies a convolution matrix acting as a low-pass filter on each signal point, with a twist: when the point is at the maximum (0 dB), the signal is totally filtered, while near zero, the dry signal stays almost untouched. The default application function is non-linear (a power of x curve) in order to convolve mostly when approaching the maximum intensity. The processing speed depends on the nature and the complexity of the function. Interestingly, additional high-order harmonics (unwanted low-intensity noise) are created while applying the low-pass filter.
The first control, Compression, applies this effect to the selection through a recursive sine function, a bit of asymmetric clipping being added to make things interesting. 0 does nothing; its maximum is way too much for this plugin's purposes, generating a truckload of harmonics and distortion. I know you will try.
The second slider, Selectivity, controls the exponential function parameter.
exp(0) = 1 means the signal is totally filtered, leading to a severe loss of
high frequencies, while exp(10) means only the very few samples near 0dB are
affected.
The third one, Efficiency, gives the (always odd) number of filter coefficients which are used to smooth out the signal: 5, 7, 9... 25 (here, 12=13, 14=15, etc.) More coefficients give a lower cutoff frequency, if there is such a thing when filtering varies with the wavepoints' amplitude. This control, along with the second one, give usually a subtle result - as it should.
The last one, Volume, is used to reduce the gain when it gets massive.
To sum up, the idea is to create a lot of harmonics, then weed them out selectively in the higher parts of the signal in order to attenuate distortion harshness.
Copyright (C) Jean Zundel [email protected] 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.
A precompiled Darwin/MacOSX binary, built on 2012-05-02, is available at
http://jzu.free.fr/Binaries/osx-satana_4742.so
for easy installation. It should be copied in
/Library/Audio/Plug-ins/LADSPA (system-wide install) or
~/Library/Audio/Plug-ins/LADSPA (user local install).
Once the satana_4742.so library has been copied to /usr/lib/ladspa/ (or
any other suitable installation folder),
enter Audacity and choose a victim^W track. Go to
Effects > Modules... > Satana.... You can begin by setting Compression to
2, Selectivity to 5 and Efficiency to 15, then experiment with
other, bolder values.
This plugin serves several purposes. You can use it to soften a digitally-clipped track (Compression to 0, Selectivity and Efficiency at mid-course); you can "enhance" the sound with compression; you can also massively distort it (set Compression to 10 and, for what it's worth, a low value for Selectivity, and Efficiency above 15).
(¹) Not too perfect with Ardour yet, but getting usable. One can hear constant-intensity crackles when Volume is down, like a kind of echo to the original signal. Doesn't happen with other sofware.