# vDSP_hann_windowD Creates a double-precision Hann window. ``` extern void vDSP_hann_windowD(double *__C, vDSP_Length __N, int __Flag); ``` ## Parameters `__C` The output vector. `__N` The number of elements in the output vector. `__Flag` A value that specifies the type of window that the function creates. - specifies that the function creates a denormalized window. - | specifies that the function creates a denormalized window with only the first `(N+1)/2` points. - specifies that the function creates a normalized window. - | specifies that the function creates a normalized window with only the first `(N+1)/2` points. ## Discussion The [`vDSP_hann_window`](/documentation/Accelerate/vDSP_hann_window) and [`vDSP_hann_windowD`](/documentation/Accelerate/vDSP_hann_windowD) functions create a Hann window vector using the following operation: ```swift 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`](/documentation/Accelerate/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: ```swift 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`:  --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)