transposed direct form 2

FluidSynth · Jun 26, 2024 · e51a527 · e51a527
1 parent f8549e2
commit e51a527
Showing 1 changed file with 11 additions and 5 deletions.
diff --git a/src/rvoice/fluid_iir_filter.c b/src/rvoice/fluid_iir_filter.c
@@ -83,7 +83,7 @@ fluid_iir_filter_apply(fluid_iir_filter_t *iir_filter,
         * doesn't change.
         */
 
-        if(dsp_filter_coeff_incr_count > 0)
+        if(0)
         {
             fluid_real_t dsp_a1_incr = iir_filter->a1_incr;
             fluid_real_t dsp_a2_incr = iir_filter->a2_incr;
@@ -123,10 +123,16 @@ fluid_iir_filter_apply(fluid_iir_filter_t *iir_filter,
             for(dsp_i = 0; dsp_i < count; dsp_i++)
             {
                 /* The filter is implemented in Direct-II form. */
-                dsp_centernode = dsp_buf[dsp_i] - dsp_a1 * dsp_hist1 - dsp_a2 * dsp_hist2;
-                dsp_buf[dsp_i] = dsp_b02 * (dsp_centernode + dsp_hist2) + dsp_b1 * dsp_hist1;
-                dsp_hist2 = dsp_hist1;
-                dsp_hist1 = dsp_centernode;
+                //dsp_centernode = dsp_buf[dsp_i] - dsp_a1 * dsp_hist1 - dsp_a2 * dsp_hist2;
+                //dsp_buf[dsp_i] = dsp_b02 * (dsp_centernode + dsp_hist2) + dsp_b1 * dsp_hist1;
+                //dsp_hist2 = dsp_hist1;
+                //dsp_hist1 = dsp_centernode;
+
+                /* The filter is implemented in Transposed Direct Form II */
+                fluid_real_t dsp_input = dsp_buf[dsp_i];
+                dsp_buf[dsp_i] = dsp_b02 * dsp_input + dsp_hist1;
+                dsp_hist1 = dsp_b1 * dsp_input - dsp_a1 * dsp_buf[dsp_i] + dsp_hist2;
+                dsp_hist2 = dsp_b02 * dsp_input - dsp_a2 * dsp_buf[dsp_i];
             }
         }