lowpass: symmetric code
@@ -25,7 +25,7 @@ impl<N: ArrayLength<i32>> Lowpass<N> {
// Note the zero(s) at Nyquist and the benign overflow (DF-I).
let mut x0 = x;
let mut x1 = self.xy[0];
- self.xy[0] = x;
+ self.xy[0] = x0;
for y1 in self.xy[1..].iter_mut() {
x0 = *y1 + (((x0 >> 1) + (x1 >> 1) - *y1 + (1 << (k - 1))) >> k);
x1 = *y1;
