/// <summary>
/// Audio EQ Cookbook に依った Bi-Quad フィルタ
/// </summary>
/// <param name="input"></param>
/// <param name="b0"></param>
/// <param name="b1"></param>
/// <param name="b2"></param>
/// <param name="a0"></param>
/// <param name="a1"></param>
/// <param name="a2"></param>
/// <returns></returns>
public static Node <float> BiQuadFilter(Node <float> input,
Node <float> b0, Node <float> b1, Node <float> b2,
Node <float> a0, Node <float> a1, Node <float> a2)
{
IEnumerable <float> signal()
{
var inDelay = new DelayBuffer <float>(2);
var outDelay = new DelayBuffer <float>(2);
foreach (var values in input.UseAsStream().Zip(
b0.UseAsStream(),
b1.UseAsStream(),
b2.UseAsStream(),
a0.UseAsStream(),
a1.UseAsStream(),
a2.UseAsStream(),
Tuple.Create))
{
var inValue = values.Item1;
var b0_ = values.Item2;
var b1_ = values.Item3;
var b2_ = values.Item4;
var a0_ = values.Item5;
var a1_ = values.Item6;
var a2_ = values.Item7;
var outValue = (b0_ * inValue + b1_ * inDelay[0] + b2_ * inDelay[-1] - a1_ * outDelay[0] - a2_ * outDelay[-1]) / a0_;
inDelay.Push(inValue);
outDelay.Push(outValue);
yield return(outValue);
}
}
return(Node.Create(signal(), true, input, b0, b1, b2, a0, a1, a2));
}
public static Node <float> Delay(this Node src, Node time_smp, Node feedbackLevel, Node wetLevel, int maxTime_smp)
{
var buffer = new DelayBuffer <float>(maxTime_smp);
IEnumerable <float> signal()
{
foreach (var stfw in src.AsFloat().UseAsStream().Zip(
time_smp.AsInt().UseAsStream(),
feedbackLevel.AsFloat().UseAsStream(),
wetLevel.AsFloat().UseAsStream(),
Tuple.Create))
{
// TODO 添字が誤っていないかチェック
yield return(stfw.Item1 + buffer[-(stfw.Item2 - 1)] * stfw.Item4);
buffer.Push(stfw.Item1 + stfw.Item3 * buffer[-(stfw.Item2 - 1)]);
}
}
return(Node.Create(signal(), true, src, time_smp, feedbackLevel, wetLevel));
}
