Revert AdaptiveNotchCPZ

It's not clear, but the modified version seems to adapt faster than the original.

common/dsp/adaptivefilter.js

@@ -37,8 +37,8 @@ export class AdaptiveFilterLMS {
  }
 }
 
-// Constrained poles and zeros-based adaptive notch filters (CPZ-ANF) described in section
-// II of following paper.
+// Adaptive notch filter based on the one described in section II of the paper below.
+// Computation of `s0` is modified from the paper.
 // - "DSP Implementation of Adaptive Notch Filters With Overflow Avoidance in Fixed-Point
 // Arithmetic" by Satoru Ishibashi, Shunsuke Koshita, Masahide Abe and Masayuki
 // Kawamata. (http://www.apsipa.org/proceedings/2018/pdfs/0001355.pdf)
@@ -83,9 +83,8 @@ export class AdaptiveNotchCPZ {
  const gain
  = this.a >= 0 ? (1 + a1 + a2) / (2 + this.a) : (1 - a1 + a2) / (2 - this.a);
 
- const denom = a1 * this.y1 + a2 * this.y2
- const y0 = x0 + this.a * this.x1 + this.x2 - denom;
- const s0 = (1 - this.rho) * x0 - this.rho * (1 - this.rho) * this.x2 - denom;
+ const y0 = x0 + this.a * this.x1 + this.x2 - a1 * this.y1 - a2 * this.y2;
+ const s0 = this.x1 * (1 - this.rho * y0);
  this.a = clamp(this.a - 2 * y0 * s0 * this.mu, -this.aBound, this.aBound);
 
  this.x2 = this.x1;