[gst-devel] gst-bad equalizer element

[Stefan Kost]

Hi,

I was browsin the sources too and found its using:

/* args are in the range [-1 ... 1] with 0 meaning "no action"
  * convert to [-0.2 ... 1] with 0 meaning no action via the function
  * f(x) = 0.25 * 5 ^ x - 0.25
  */
static gdouble
arg_to_scale (gdouble arg)
{
   return 0.25 * exp (log (5) * arg) - 0.25;
}

This does not look like its doing a db  
(http://en.wikipedia.org/wiki/Decibel) mapping. If '0' is no action  
(factor 1.0) is a:
* value of 1 then meaning factor+1=2 aka double volume (+3db) and
* value of -1 then meaning a fifth of the volume (somewhere around -7db)
Thats what I assume, but maybe company can clarify. If its like this  
it should be changed. The range is a bit too small imho. E.g. the EQ  
in winamp it goes from -12db to 12 db (in media player it goes from  
-14 to +14 whatever). I'd say -12 to +6 sounds good.

Stefan

Quoting Christophe Dehais <christophe.dehais at gmail.com>:

> Hi !
>
> The equalizer element has been ported to 0.10 and is currently in gst-bad CVS
>
> I'm making a plugin for rhythmbox that uses this element, however I
> don't understand precisely what the properties mean:
>
> - num-bands seems to specify the partition of the spectrum but what is
> the min and max frequency ? And I guess that it's not regularly
> divided, so what  scheme is used ?
> - band-values holds values in [-1.0; 1.0]. Is this mappable to
> something in decibels ?
>
> I browsed rapidly through the code, and I thought I was not good
> enough in signal theory to answer this whithout further research, so I
> would appreciate any help from someone who knows (maybe the author of
> the element ?)
>
> thanks,
>
> Christophe
>
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