Hanning and Hamming window functions in C#

Question

I'm trying to implement Hanning and Hamming window functions in C#. I can't find any.Net samples anywhere and I'm not sure if my attempts at converting from C++ samples does the job well.

My problem is mainly that looking at the formulas I imagine they need to have the original number somewhere on the right hand side of the equation - I just don't get it from looking at the formulas. (My math isn't that good yet obviously.)

What I have so far:

public Complex[] Hamming(Complex[] iwv)
{
    Complex[] owv = new Complex[iwv.Length];
    double omega = 2.0 * Math.PI / (iwv.Length);

    // owv[i].Re = real number (raw wave data)
    // owv[i].Im = imaginary number (0 since it hasn't gone through FFT yet)
    for (int i = 1; i < owv.Length; i++)
        // Translated from c++ sample I found somewhere
        owv[i].Re = (0.54 - 0.46 * Math.Cos(omega * (i))) * iwv[i].Re; 

    return owv;

}

public Complex[] Hanning(Complex[] iwv)
{
    Complex[] owv = new Complex[iwv.Length];
    double omega = 2.0 * Math.PI / (iwv.Length);

    for (int i = 1; i < owv.Length; i++)
        owv[i].Re = (0.5  + (1 - Math.Cos((2d * Math.PI ) / (i -1)))); // Uhm... wrong

    return owv;
}

Answer 1

Here's an example of a Hamming window in use in an open source C# application I wrote a while back. It's being used in a pitch detector for an autotune effect .

Answer 2

You can use the Math.NET library.

    double[] hannDoubles = MathNet.Numerics.Window.Hamming(dataIn.Length);
    for (int i = 0; i < dataIn.Length; i++)
    {
        dataOut[i] = hannDoubles[i] * dataIn[i];
    }

See my answer to a similar question: https://stackoverflow.com/a/42939606/246758

Answer 3

The operation of "windowing" means multiplying a signal by a window function. This code you found appears to generate the window function and scale the original signal. The equations are for just the window function itself, not the scaling.