FIfWinHCos

Routine

void FIfWinHCos (float win[], double T1, double T2, double T3, double a)

Purpose

Generate a Hamming/cosine window

Description

Consider the continuous-time variable t. The half Hamming window starts at t=0, and reaches its peak value (unity) at t=T1. The window is constant at unity from t=T1 to t=T2. The quarter cycle cosine window is unity at t=T2 and decreases to zero at t=T3.

       = 0 ,                            t  < 0
                        pi t
       = (1-a) - a cos (----) ,    0 <= t < T1
                         T1
  h(t) = 1 ,                      T1 <= t < T2
              pi (t-T2)
       = cos (---------) ,        T2 <= t < T3
              2 (T3-T2)
       = 0 ,                      T3 <= t

A window of this form is used for the ITU-T G.729 8 kb/s coder and its derivatives. The G.729 discrete-time window has 240 non-zero samples, and is obtained by setting a = 0.46, T1 = 199.5, T2 = 200, T3 = 239.75. The discrete-time window is sampled at t = i, with 0 <= i < 240. The G.729 window can be obtained with the following call

  FIwinHCos (win, 199.5, 200.0, 239.75, 0.46)

Parameters

<- float win[]

Array containing the window values

-> double T1

Length of the half Hamming window.

-> double T2

End point of the constant region, T2 >= T1.

-> double T3

End point of the quarter cycle cosine rollof, T3 >= T2. The number of points in the window is floor (T3) + 1.

-> double a

Window parameter for the first part of the window; a=0.46 for a conventional Hamming window, a=0.5 for a full raised-cosine window, a=0 for a rectangular window. The window is non-negative for 0 <= a <= 0.5.

Author / revision

See Also