[pulseaudio-discuss] Dynamic range compression

[Mikhail Morfikov]

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On 2015-09-29 10:03, Tanu Kaskinen wrote:
> On Tue, 2015-09-29 at 09:38 +0200, Mikhail Morfikov wrote:
>> 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.
> 
> The last two controls are outputs, so if the plugin host supports it
> (PulseAudio doesn't), other plugins can use those last two controls as
> inputs. You only set values for input controls, which is why you only
> need to set 7 values.

I get it now. Thanks!

>> 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?
> 
> So you'd like to confirm that PulseAudio sets the values correctly?
> There is an undocumented API to set and get the control values at
> runtime. I don't want to document it here, sorry. I recommend you to
> just trust that the controls are set to the values that you specify
> when loading the module.
> 


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