Re: [fluid-dev] [PATCH] Effect level clip

[Josh Green]

Hello David,

Thank you for the patch.  It addresses a problem that has been bothering
me for some time (the increase of volume with Chorus and Reverb
effects).  Sounds great too :)  I had realized that Chorus and Reverb
effects had a tendency to make things sound really bad, mainly because
of digital clipping.  This seems to minimize that effect.

I have a question about your patch though, before I apply it.

As far as adjusting the values for qsynth's center.  Is that necessary?
Or would it be better to modify QSynth?  It would be nice to keep
backwards compatibility as much as makes sense.  Since FluidSynth is
used by a number of applications.  Perhaps this change is fine though, I
would just like to be sure its not arbitrary and only for qsynth.

Thanks again for the contribution.
        Josh

P.S. I created a ticket for this patch here:
http://fluidsynth.resonance.org/trac/ticket/2


On Tue, 2007-07-31 at 09:53 -0500, David Hilvert wrote:
> Overview
> 
> The following patch moves effect level adjustments prior to the send clip, and
> reduces the chorus effect linearly with the number of voices.  These changes
> seem to make output (volume) levels more uniform; in particular, the 
> phenomenon
> of certain instruments with high choral component being several times louder
> than those with low choral component seems to be mitigated across a variety of
> synthesizer parameter settings.
> 
> Notes
> 
> - The magnitude of the choral effect for large N is reduced by this patch; 
> some
>   reduction is also present at smaller N.
> 
> - Effect level defaults have been adjusted so that qsynth's center is neutral.
>   Better might be to balance the scale around 0, with 0 neutral.
> 
> - The patch is against version 1.0.7a.
> 
> 
> Patch follows.
> 
> 
> diff -ubr fluidsynth-1.0.7/include/fluidsynth/synth.h 
> fluidsynth-modified/include/fluidsynth/synth.h
> --- fluidsynth-1.0.7/include/fluidsynth/synth.h       2005-06-12 
> 01:19:37.000000000 +0000
> +++ fluidsynth-modified/include/fluidsynth/synth.h    2007-07-30 
> 22:12:06.000000000 +0000
> @@ -291,7 +291,7 @@
>  #define FLUID_REVERB_DEFAULT_ROOMSIZE 0.2f
>  #define FLUID_REVERB_DEFAULT_DAMP 0.0f
>  #define FLUID_REVERB_DEFAULT_WIDTH 0.5f
> -#define FLUID_REVERB_DEFAULT_LEVEL 0.9f
> +#define FLUID_REVERB_DEFAULT_LEVEL 0.5f
>  
> 
> 
> @@ -325,7 +325,7 @@
>  
>    /* Those are the default settings for the chorus. */
>  #define FLUID_CHORUS_DEFAULT_N 3
> -#define FLUID_CHORUS_DEFAULT_LEVEL 2.0f
> +#define FLUID_CHORUS_DEFAULT_LEVEL 6.25f
>  #define FLUID_CHORUS_DEFAULT_SPEED 0.3f
>  #define FLUID_CHORUS_DEFAULT_DEPTH 8.0f
>  #define FLUID_CHORUS_DEFAULT_TYPE FLUID_CHORUS_MOD_SINE 
> diff -ubr fluidsynth-1.0.7/src/fluid_chorus.c 
> fluidsynth-modified/src/fluid_chorus.c
> --- fluidsynth-1.0.7/src/fluid_chorus.c       2003-03-11 16:57:10.000000000 
> +0000
> +++ fluidsynth-modified/src/fluid_chorus.c    2007-07-30 23:07:08.000000000 
> +0000
> @@ -477,7 +477,8 @@
>        chorus->phase[i] %= (chorus->modulation_period_samples);
>      } /* foreach chorus block */
>  
> -    d_out *= chorus->level;
> +    if (chorus->number_blocks)
> +      d_out /= chorus->number_blocks;
>      
>      /* Add the chorus sum d_out to output */
>      left_out[sample_index] += d_out;
> @@ -544,7 +545,8 @@
>        chorus->phase[i] %= (chorus->modulation_period_samples);
>      } /* foreach chorus block */
>  
> -    d_out *= chorus->level;
> +    if (chorus->number_blocks)
> +      d_out /= chorus->number_blocks;
>      
>      /* Add the chorus sum d_out to output */
>      left_out[sample_index] = d_out;
> diff -ubr fluidsynth-1.0.7/src/fluid_rev.c fluidsynth-modified/src/fluid_rev.c
> --- fluidsynth-1.0.7/src/fluid_rev.c  2004-03-29 10:05:18.000000000 +0000
> +++ fluidsynth-modified/src/fluid_rev.c       2007-07-30 22:04:24.000000000 
> +0000
> @@ -272,6 +272,7 @@
>    fluid_real_t roomsize;
>    fluid_real_t damp;
>    fluid_real_t wet, wet1, wet2;
> +  fluid_real_t level;
>    fluid_real_t width;
>    fluid_real_t gain;
>    /*
> @@ -534,15 +535,13 @@
>  void 
>  fluid_revmodel_setlevel(fluid_revmodel_t* rev, fluid_real_t value)
>  {
> -/*   fluid_clip(value, 0.0f, 1.0f); */
> -/*   rev->wet = value * scalewet; */
> -/*   fluid_revmodel_update(rev); */
> +     rev->level = value;
>  }
>  
>  fluid_real_t 
>  fluid_revmodel_getlevel(fluid_revmodel_t* rev)
>  {
> -  return rev->wet / scalewet;
> +  return rev->level;
>  }
>  
>  void 
> diff -ubr fluidsynth-1.0.7/src/fluid_synth.c 
> fluidsynth-modified/src/fluid_synth.c
> --- fluidsynth-1.0.7/src/fluid_synth.c        2006-02-19 07:19:07.000000000 
> +0000
> +++ fluidsynth-modified/src/fluid_synth.c     2007-07-30 22:06:44.000000000 
> +0000
> @@ -1762,6 +1762,8 @@
>    fluid_real_t* chorus_buf;
>    int byte_size = FLUID_BUFSIZE * sizeof(fluid_real_t);
>    double prof_ref = fluid_profile_ref();
> +  fluid_real_t chorus_level = fluid_chorus_get_level(synth->chorus);
> +  fluid_real_t reverb_level = fluid_revmodel_getlevel(synth->reverb);
>  
>  /*   fluid_mutex_lock(synth->busy); /\* Here comes the audio thread. Lock 
> the synth. *\/ */
>    
> @@ -1820,11 +1822,20 @@
>        left_buf = synth->left_buf[auchan];
>        right_buf = synth->right_buf[auchan];
>  
> +      fluid_voice_set_param(voice, GEN_CHORUSSEND,
> +                            1000.0
> +                          * (chorus_level - FLUID_CHORUS_DEFAULT_LEVEL) 
> +                          / FLUID_CHORUS_DEFAULT_LEVEL, 1 /* ? */);
> +      fluid_voice_set_param(voice, GEN_REVERBSEND,
> +                            1000.0
> +                          * (reverb_level - FLUID_REVERB_DEFAULT_LEVEL) 
> +                          / FLUID_REVERB_DEFAULT_LEVEL, 1 /* ? */);
>        fluid_voice_write(voice, left_buf, right_buf, reverb_buf, chorus_buf);
>  
>        fluid_profile(FLUID_PROF_ONE_BLOCK_VOICE, prof_ref_voice);
>      }
>    }
> +
>    fluid_check_fpe("Synthesis processes");
>  
>    fluid_profile(FLUID_PROF_ONE_BLOCK_VOICES, prof_ref);
> 
> 
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