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Prevent the IIR filter from loud pops on quick frequency changes (ticket #82)

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This commit is contained in:
David Henningsson 2011-03-27 16:59:15 +00:00
parent f7d87aa1a8
commit d8aad67d8d
1 changed files with 15 additions and 4 deletions
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19
fluidsynth/src/rvoice/fluid_iir_filter.c
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@ -56,10 +56,6 @@ fluid_iir_filter_apply(fluid_iir_filter_t* iir_filter,
fluid_real_t dsp_a2 = iir_filter->a2;
fluid_real_t dsp_b02 = iir_filter->b02;
fluid_real_t dsp_b1 = iir_filter->b1;
fluid_real_t dsp_a1_incr = iir_filter->a1_incr;
fluid_real_t dsp_a2_incr = iir_filter->a2_incr;
fluid_real_t dsp_b02_incr = iir_filter->b02_incr;
fluid_real_t dsp_b1_incr = iir_filter->b1_incr;
int dsp_filter_coeff_incr_count = iir_filter->filter_coeff_incr_count;
fluid_real_t dsp_centernode;
@ -77,6 +73,12 @@ fluid_iir_filter_apply(fluid_iir_filter_t* iir_filter,
if (dsp_filter_coeff_incr_count > 0)
{
fluid_real_t dsp_a1_incr = iir_filter->a1_incr;
fluid_real_t dsp_a2_incr = iir_filter->a2_incr;
fluid_real_t dsp_b02_incr = iir_filter->b02_incr;
fluid_real_t dsp_b1_incr = iir_filter->b1_incr;
/* Increment is added to each filter coefficient filter_coeff_incr_count times. */
for (dsp_i = 0; dsp_i < count; dsp_i++)
{
@ -88,10 +90,19 @@ fluid_iir_filter_apply(fluid_iir_filter_t* iir_filter,
if (dsp_filter_coeff_incr_count-- > 0)
{
fluid_real_t old_b02 = dsp_b02;
dsp_a1 += dsp_a1_incr;
dsp_a2 += dsp_a2_incr;
dsp_b02 += dsp_b02_incr;
dsp_b1 += dsp_b1_incr;
/* Compensate history to avoid the filter going havoc with large frequency changes */
if (fabs(dsp_b02) > 0.001) {
fluid_real_t compensate = old_b02 / dsp_b02;
dsp_centernode *= compensate;
dsp_hist1 *= compensate;
dsp_hist2 *= compensate;
}
}
} /* for dsp_i */
}