[vlc-devel] [PATCH 2/4] Adds the compressor module to VLC
Ron Wright
logiconcepts819 at gmail.com
Thu Jul 1 21:49:56 CEST 2010
Hi,
On Thu, Jul 1, 2010 at 1:10 PM, Laurent Aimar <fenrir at elivagar.org> wrote:
> Hi,
>
> On Thu, Jul 01, 2010 at 03:33:00AM -0500, Ronald Wright wrote:
> > +vlc_module_begin()
> > + set_shortname( _("Compressor") )
> > + set_description( _("Dynamic range compressor") )
> > + set_capability( "audio filter", 1 )
> It must be 0 as explained in reply to another of your patches.
>
See below for the explanation of the issue.
> > + add_float( "compressor-lo-pregain", 0.0, NULL, LO_TEXT,
> > + LO_LONGTEXT, false )
> > + add_float( "compressor-mid-pregain", 0.0, NULL, MID_TEXT,
> > + MID_LONGTEXT, false )
> > + add_float( "compressor-hi-pregain", 0.0, NULL, HI_TEXT,
> > + HI_LONGTEXT, false )
>
> I don't see why you have to do the equalizer part inside your module.
> I think that normalizing the audio and applying equalization are two
> completly independant tasks, and as such should be done by two
> independant plugin. Furthermore, we already have 2 equalizers in VLC.
>
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"?)
> > +static int Open( vlc_object_t *p_this )
> > +{
> > + filter_t *p_filter = (filter_t*)p_this;
> > + vlc_object_t *p_aout = p_filter->p_parent;
> > + float f_sample_rate = p_filter->fmt_in.audio.i_rate;
> > + struct filter_sys_t *p_sys;
> > + float f_num;
> > +
> > + if( p_filter->fmt_in.audio.i_format != VLC_CODEC_FL32 ||
> > + p_filter->fmt_out.audio.i_format != VLC_CODEC_FL32 )
> > + {
> > + p_filter->fmt_in.audio.i_format = VLC_CODEC_FL32;
> > + p_filter->fmt_out.audio.i_format = VLC_CODEC_FL32;
> > + msg_Warn( p_filter, "bad input or output format" );
> > + return VLC_EGENERIC;
> > + }
> > + if( !AOUT_FMTS_SIMILAR( &p_filter->fmt_in.audio,
> > + &p_filter->fmt_out.audio ) )
> > + {
> > + p_filter->fmt_out.audio = p_filter->fmt_in.audio;
> > + msg_Warn( p_filter, "input and output formats are not similar"
> );
> > + return VLC_EGENERIC;
> > + }
> > +
> > + /* Initialize the filter parameter structure */
> > + p_sys = p_filter->p_sys = calloc( 1, sizeof(*p_sys) );
> > + if( !p_sys )
> > + {
> > + return VLC_ENOMEM;
> > + }
> > +
> > + /* Initialize the attack lookup table */
> > + p_sys->pf_as[0] = 1.0f;
> > + for( int i = 1; i < A_TBL; i++ )
> > + {
> > + p_sys->pf_as[i] = expf( -1.0f / ( f_sample_rate * i / A_TBL ) );
> > + }
> > +
> > + /* Calculate the RMS and lookahead sizes from the sample rate */
> > + f_num = 0.01f * f_sample_rate;
> > + p_sys->rms.i_count = Round( Clamp( 0.5f * f_num, 1.0f, RMS_BUF_SIZE
> ) );
> > + p_sys->la.i_count = Round( Clamp( f_num, 1.0f, LOOKAHEAD_SIZE ) );
> > +
> > + /* Initialize decibel lookup tables */
> > + DbInit( p_sys );
> > +
> > + /* Restore the last saved settings */
> > + p_sys->f_lo_pregain =
> > + var_CreateGetFloat( p_aout, "compressor-lo-pregain" );
> > + p_sys->f_mid_pregain =
> > + var_CreateGetFloat( p_aout, "compressor-mid-pregain" );
> > + p_sys->f_hi_pregain =
> > + var_CreateGetFloat( p_aout, "compressor-hi-pregain" );
> > + p_sys->f_rms_peak = var_CreateGetFloat( p_aout,
> "compressor-rms-peak" );
> > + p_sys->f_attack = var_CreateGetFloat( p_aout,
> "compressor-attack" );
> > + p_sys->f_release = var_CreateGetFloat( p_aout,
> "compressor-release" );
> > + p_sys->f_threshold = var_CreateGetFloat( p_aout,
> "compressor-threshold" );
> > + p_sys->f_ratio = var_CreateGetFloat( p_aout,
> "compressor-ratio" );
> > + p_sys->f_knee = var_CreateGetFloat( p_aout, "compressor-knee"
> );
> > + p_sys->f_makeup_gain =
> > + var_CreateGetFloat( p_aout, "compressor-makeup-gain" );
> > +
> > + /* Initialize the mutex */
> > + vlc_mutex_init( &p_sys->lock );
> > +
> > + /* Add our own callbacks */
> > + var_AddCallback( p_aout, "compressor-lo-pregain", LoPregainCallback,
> > + p_sys );
> > + var_AddCallback( p_aout, "compressor-mid-pregain",
> MidPregainCallback,
> > + p_sys );
> > + var_AddCallback( p_aout, "compressor-hi-pregain", HiPregainCallback,
> > + p_sys );
> > + var_AddCallback( p_aout, "compressor-rms-peak", RMSPeakCallback,
> p_sys );
> > + var_AddCallback( p_aout, "compressor-attack", AttackCallback, p_sys
> );
> > + var_AddCallback( p_aout, "compressor-release", ReleaseCallback,
> p_sys );
> > + var_AddCallback( p_aout, "compressor-threshold", ThresholdCallback,
> p_sys );
> > + var_AddCallback( p_aout, "compressor-ratio", RatioCallback, p_sys );
> > + var_AddCallback( p_aout, "compressor-knee", KneeCallback, p_sys );
> > + var_AddCallback( p_aout, "compressor-makeup-gain",
> MakeupGainCallback,
> > + p_sys );
> > +
> > + /* Set the filter function */
> > + p_filter->pf_audio_filter = DoWork;
> > +
> > + /* At this stage, we are ready! */
> > + msg_Dbg( p_filter, "compressor successfully initialized" );
> > + return VLC_SUCCESS;
> > +}
> > +
> >
> +/*****************************************************************************
> > + * Close: destroy interface
> > +
> *****************************************************************************/
> > +
> > +static void Close( vlc_object_t *p_this )
> > +{
> > + filter_t *p_filter = (filter_t*)p_this;
> > + vlc_object_t *p_aout = p_filter->p_parent;
> > + struct filter_sys_t *p_sys = p_filter->p_sys;
> > +
> > + /* Remove our callbacks */
> > + var_DelCallback( p_aout, "compressor-rms-peak", RMSPeakCallback,
> p_sys );
> > + var_DelCallback( p_aout, "compressor-attack", AttackCallback, p_sys
> );
> > + var_DelCallback( p_aout, "compressor-release", ReleaseCallback,
> p_sys );
> > + var_DelCallback( p_aout, "compressor-threshold", ThresholdCallback,
> p_sys );
> > + var_DelCallback( p_aout, "compressor-ratio", RatioCallback, p_sys );
> > + var_DelCallback( p_aout, "compressor-knee", KneeCallback, p_sys );
> > + var_DelCallback( p_aout, "compressor-makeup-gain",
> MakeupGainCallback,
> > + p_sys );
> 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. I have been too busy fixing other things in
the code, and when I make many changes, it is hard to keep track of the
remaining changes that I still have to take care of.
> Regards,
>
> --
> fenrir
>
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>
Regards,
Ronald Wright
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