[pulseaudio-discuss] Dynamic range compression

[Felipe Sateler]

On 28 September 2015 at 10:43, Tanu Kaskinen <tanuk at iki.fi> wrote:
> On Mon, 2015-09-28 at 15:30 +0200, Mikhail Morfikov wrote:
>> A few days ago I found a module called module-ladspa-sink ,
>> and it can be enabled by adding the following code to the
>> /etc/pulse/default.pa file:
>>
>> .ifexists module-ladspa-sink.so
>> .nofail
>> load-module module-ladspa-sink sink_name=compressor plugin=sc4m_1916
>> label=sc4m control=1,1.5,401,-30,20,5,12
>> .fail
>> .endif
>>
>> It works, but I was trying to figure out what exactly
>> control=1,1.5,401,-30,20,5,12 means. There's a link
>> (http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html#tth_sEc2.92),
>> where you can find some documentation on the sc4m_1916 plugin,
>> but actually I don't really know which of the values corresponds
>> to the specific options. In the link, there's 9 parameters,
>> and in the code above, there's 7 I think.
>>
>> Is there someone who could cast a little light on the control
>> numbers?
>
> module-ladspa-sink fails to load if you don't provide all parameters,
> so if it works, the plugin really has only 7 control parameters. I
> don't know how you then should map them to the documentation. There
> very likely is some handy little program somewhere that you could use
> to inspect the plugin, but the only one that I can mention off the top
> of my head is JACK Rack, but that obviously depends on JACK, and if you
> don't already use JACK, it can be a bit of a hassle to set it up. I'd
> expect there to be some simple command line ladspa plugin inspector
> program too that doesn't need any audio access.

There is analyseplugin that is part of the ladspa sdk:

% analyseplugin sc4m_1916

Plugin Name: "SC4 mono"
Plugin Label: "sc4m"
Plugin Unique ID: 1916
Maker: "Steve Harris <steve at plugin.org.uk>"
Copyright: "GPL"
Must Run Real-Time: No
Has activate() Function: No
Has deactivate() Function: No
Has run_adding() Function: Yes
Environment: Normal or Hard Real-Time
Ports:  "RMS/peak" input, control, 0 to 1, default 0
       "Attack time (ms)" input, control, 1.5 to 400, default 101.125
       "Release time (ms)" input, control, 2 to 800, default 401
       "Threshold level (dB)" input, control, -30 to 0, default 0
       "Ratio (1:n)" input, control, 1 to 20, default 1
       "Knee radius (dB)" input, control, 1 to 10, default 3.25
       "Makeup gain (dB)" input, control, 0 to 24, default 0
       "Amplitude (dB)" output, control, -40 to 12
       "Gain reduction (dB)" output, control, -24 to 0
       "Input" input, audio
       "Output" output, audio

-- 

Saludos,
Felipe Sateler