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added biquad allpass filter

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This commit is contained in:
Ahmet Inan 2019-03-03 11:08:40 +01:00
commit 55048b527b
2 changed files with 17 additions and 0 deletions
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1
README.md
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@ -41,6 +41,7 @@ The following [infinite impulse response](https://en.wikipedia.org/wiki/Infinite
* [2n-order Butterworth cascade of second-order low or high pass filters](https://en.wikipedia.org/wiki/Butterworth_filter) * [2n-order Butterworth cascade of second-order low or high pass filters](https://en.wikipedia.org/wiki/Butterworth_filter)
* [second-order notch filter](https://en.wikipedia.org/wiki/Band-stop_filter) * [second-order notch filter](https://en.wikipedia.org/wiki/Band-stop_filter)
* [second-order bandpass filter](https://en.wikipedia.org/wiki/Band-pass_filter) * [second-order bandpass filter](https://en.wikipedia.org/wiki/Band-pass_filter)
* [second-order allpass filter](https://en.wikipedia.org/wiki/All-pass_filter)
### [blockdc.hh](blockdc.hh) ### [blockdc.hh](blockdc.hh)

16
biquad.hh
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@ -86,6 +86,22 @@ public:
a1a0 = a1 / a0; a1a0 = a1 / a0;
a2a0 = a2 / a0; a2a0 = a2 / a0;
} }
void allpass(int n, int N, VALUE QdB)
{
VALUE alpha = UnitCircle<VALUE>::sin(n, N) / (VALUE(2) * idecibel(QdB)),
cn = UnitCircle<VALUE>::cos(n, N),
b0 = VALUE(1) - alpha,
b1 = -VALUE(2) * cn,
b2 = VALUE(1) + alpha,
a0 = VALUE(1) + alpha,
a1 = -VALUE(2) * cn,
a2 = VALUE(1) - alpha;
b0a0 = b0 / a0;
b1a0 = b1 / a0;
b2a0 = b2 / a0;
a1a0 = a1 / a0;
a2a0 = a2 / a0;
}
TYPE operator()(TYPE x0) TYPE operator()(TYPE x0)
{ {
TYPE y0 = b0a0*x0 + b1a0*x1 + b2a0*x2 TYPE y0 = b0a0*x0 + b1a0*x1 + b2a0*x2