[pulseaudio-discuss] Dynamic range compression

[Mikhail Morfikov]

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On 2015-09-28 15:51, Felipe Sateler wrote:
> 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
> 

Thanks for the hint. I have one question though. Is there a tool that can
tell what settings are applied to the plugin? In the log above, there's 7 ports
that have to be set, that's why there's the default value. Also there's two other
ports that weren't set anywhere, so I think they're not taken into consideration
at all if they're not set in the control= option. I just wanted to see whether
the settings in control=1,1.5,401,-30,20,5,12 are properly set. Is there something
like that?
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