+ case FILTER_PEAKING_EQ:
+ b0 = 1 + alpha * A;
+ b1 = -2*cs;
+ b2 = 1 - alpha * A;
+ a0 = 1 + alpha / A;
+ // a1 = -2*cs;
+ a2 = 1 - alpha / A;
+ break;
+
+ case FILTER_LOW_SHELF:
+ b0 = A * ((A + 1) - (A - 1)*cs + 2 * sqrt(A) * alpha);
+ b1 = 2 * A * ((A - 1) - (A + 1)*cs );
+ b2 = A * ((A + 1) - (A - 1)*cs - 2 * sqrt(A) * alpha);
+ a0 = (A + 1) + (A - 1)*cs + 2 * sqrt(A) * alpha ;
+ a1 = -2 * ((A - 1) + (A + 1)*cs );
+ a2 = (A + 1) + (A - 1)*cs - 2 * sqrt(A) * alpha ;
+ break;
+
+ case FILTER_HIGH_SHELF:
+ b0 = A * ((A + 1) + (A - 1)*cs + 2 * sqrt(A) * alpha);
+ b1 = -2 * A * ((A - 1) + (A + 1)*cs );
+ b2 = A * ((A + 1) + (A - 1)*cs - 2 * sqrt(A) * alpha);
+ a0 = (A + 1) - (A - 1)*cs + 2 * sqrt(A) * alpha ;
+ a1 = 2 * ((A - 1) - (A + 1)*cs );
+ a2 = (A + 1) - (A - 1)*cs - 2 * sqrt(A) * alpha ;
+ break;
+