[vlc-devel] [PATCH 2/4] Adds the compressor module to VLC

[Laurent Aimar]

Hi,

On Thu, 2010-07-01 at 14:49 -0500, Ron Wright wrote:

> But then, how can you tell if the equalizer will go before or after
> the compressor on instantiation?  Priority is important when it comes
> to dynamic range compressors, as there is a significant difference
> between equalization before compression and compression before
> equalization.  Read the blue box at
> http://www.soundonsound.com/sos/jan01/articles/advanced.asp.
> 
> It's almost like asking yourself, given two distinct functions f(x)
> and g(x), is f(g(x)) really equal to g(f(x))?  The answer is obvious:
> not always, since the composition of functions is not commutative.
> This means that the audio controls in a certain order will exhibit
> behavior that changes when the order is swapped.
> 
> Here is an example.  Assume the older patches are used to compile VLC.
> Also assume that the parametric equalizer, main equalizer, and
> compressor are enabled.  Because the equalizers and compressor have
> score 0, there are six different ways for the audio to be processed,
> and four of these ways will have a major impact as to how the audio is
> output.  If the ordering is not explicit, then the compressor is not
> suitable for use with either equalizer.
> 
> Considering the information that I have just mentioned, if you can
> help me find a better way to implement the equalization part (without
> changing the scores in the other modules), let me know.  My most
> reasonable guess is that my module belongs in a category other than
> audio filters.  (Is it possible that I need to add a new module
> category known as "audio_processors"?)
 The order in which the filter are inserted is defined by the value of
the aout variable "audio-filter".
 For example "audio-filter" == "compressor:equalizer" will insert the
compressor first and then the equalizer (whatever are the modules
priority).

 This variable is updated when you call aout_EnableFilter() which then
calls AoutChangeFilterString() defined in
src/audio_output/aout_internal.h.
If you want to impose an order, you can simply modify this function.

>         
>          I think you forgot some deletes.
>         Maybe creating a table with the variables names and the
>         associated callbacks
>         would  simplify it ? Otherwise, adding the missing one is
>         enough.
> 
> Oops, I forgot to add those in.
 No problem.

-- 
fenrir