Function

vDSP_hann_windowD(_:_:_:)

Creates a double-precision Hann window.

Declaration

func vDSP_hann_windowD(_ __C: UnsafeMutablePointer<Double>, _ __N: vDSP_Length, _ __Flag: Int32)

Parameters

__C

Double-precision real output vector.

__N

The desired window length.

__Flag

The Flag parameter can have the following values:

vDSP_HANN_DENORM creates a denormalized window.
vDSP_HANN_DENORM | vDSP_HALF_WINDOW creates a denormalized window with only the first (N+1)/2 points.
vDSP_HANN_NORM creates a normalized window.
vDSP_HANN_NORM | vDSP_HALF_WINDOW creates a normalized window with only the first (N+1)/2 points.

Discussion

The vDSP_hann_window(_:_:_:) and vDSP_hann_windowD(_:_:_:) functions create a Hann window vector, using the following operation:

If Flag & vDSP_HALF_WINDOW:
    Length = (N+1)/2;
Else
    Length = N;

If Flag & vDSP_HANN_NORM:
    W = .8165;
Else
    W = .5;

for (n = 0; n < Length; ++n)
    C[n] = W * (1 - cos(2*pi*n/N));

Use vDSP_vmulD(_:_:_:_:_:_:_:) to multiply the Hann window result by a noninteger-periodic signal prior to a Fourier transform.

The following code shows how to generate a Hann window:

let n = vDSP_Length(1024)
var c = [Double](repeating: 0,
                 count: Int(n))

vDSP_hann_windowD(&c,
                  n,
                  Int32(vDSP_HANN_DENORM))

The following illustrates the values of the output vector, c:

vDSP_hann_windowD(_:_:_:)

Declaration

Parameters

Discussion

See Also

Vector Generation with Window Functions