DSP Blockset

Window Function

Compute a window, and/or apply a window to an input signal.

Library
DSP Sources, Signal Operations

Description

The Window Function block has three modes of operation, selected by the Operation parameter as described below.

Operation Modes

In each mode, the block first creates a window vector, w, by sampling the window specified in the Window type parameter at M discrete points. The Operation modes are:

• Apply window to input

In this mode the block computes an M-by-1 window vector, w, and multiplies the vector element-wise with each of the N channels in the M-by-N input matrix u.

y = repmat(w,1,N) .* u            % Equivalent MATLAB code

A length-M 1-D vector input is treated as an M-by-1 matrix. The output, y, always has the same dimension as the input. If the input is frame-based, the output is frame-based; otherwise, the output is sample-based.

• Generate window

In this mode the block generates a sample-based 1-D window vector, w, with length M specified by the Window length parameter. The In port is disabled.

• Generate and apply window

In this mode the block computes an M-by-1 window vector, w, and multiplies the vector element-wise with each of the N channels in the M-by-N input matrix u.

y = repmat(w,1,N) .* u            % Equivalent MATLAB code

A length-M 1-D vector input is treated as an M-by-1 matrix. The block produces two outputs:

• At the Out port, the block produces the result of the multiplication, y, which has the same dimension as the input. If the input is frame-based, output y is frame-based; otherwise, output y is sample-based.
• At the Win port, the block produces the M-by-1 window vector, w. Output w is always sample-based.

Window Sampling

For the generalized-cosine windows (Blackman, Hamming, and Hann), the Sampling parameter determines whether the window samples are computed in a periodic or a symmetric manner. For example, if Sampling is set to Symmetric, a Hamming window of length M is computed as

w = hamming(M)       % Symmetric (aperiodic) window

If Sampling is set to Periodic, the same window is computed as

w = hamming(M+1)     % Periodic (asymmetric) window
w = w(1:M)

Window Type

The available window types are shown in the table below. The Stopband attenuation in dB and Beta parameters specify the characteristics of the Chebyshev and Kaiser windows, respectively, and are only available when those window designs are selected.

When Window type is set to User defined, the Window function block computes the user-defined window specified by the Window function name parameter. If the user-defined window requires parameters other than the window length, select the Additional parameters for user defined window check box. The cell array entered in Window function parameters determines the values of the additional parameters.

For complete information about the other window functions, consult the Signal Processing Toolbox documentation.

Window Type	Description
Bartlett	Computes a Bartlett window. w = bartlett(M)
Blackman	Computes a Blackman window. w = blackman(M)
Boxcar	Computes a Boxcar window. w = boxcar(M)
Chebyshev	Computes a Chebyshev window with stopband ripple R. w = chebwin(M,R)
Hamming	Computes a Hamming window. w = hamming(M)
Hann	Computes a Hann window (also known as a Hanning window). w = hann(M)
Hanning	Obsolete. This window option is included only for compatibility with older models. Use the Hann option instead of Hanning whenever possible.
Kaiser	Computes a Kaiser window with Kaiser parameter beta. w = kaiser(M,beta)
Triang	Computes a triangular window. w = triang(M)
User Defined	Computes the user-defined window function specified by the entry in the Window function name parameter, usrwin. w = usrwin(M) % window takes no extra parameters w = usrwin(M,x1,...,xn) % window takes extra parameters {x1 ... xn}

Dialog Box

Operation

The block's operation: Apply window to input, Generate window, or Generate and apply window. The input/output port configuration is updated to match the parameter setting.

Window type

The type of window to apply. Tunable.

Window length

The length of the window to apply. This parameter is available only when Generate window is selected in the Operation menu. Otherwise, the window vector length is computed to match the input frame size, M.

Sampling

The window sampling for generalized-cosine windows, Symmetric or Periodic. Tunable.

Stopband attenuation in dB

(Not shown in dialog above. Visible for the Chebyshev window.) The level (dB) of stopband attenuation, R_s. Tunable.

Beta

(Not shown in dialog above. Visible for the Kaiser window.) The Kaiser window parameter. Increasing widens the mainlobe and decreases the amplitude of the window sidelobes in the window's frequency magnitude response. Tunable.

Window function name

(Not shown in dialog above. Visible for User defined windows.) The name of the user-defined window function to be calculated by the block. Tunable.

Additional parameters for user defined window

(Not shown in dialog above. Visible for User defined windows.) Enables the Window function parameters wnen selected. Select when the user-defined window requires parameters other than the window length. Tunable.

Window function parameters

(Not shown in dialog above.Visible for User defined windows.) The extra parameters required by the user-defined window function, enabled when Additional parameters for user defined window is selected. The entry must be a cell array. Tunable.

See Also

FFT	DSP Blockset
bartlett	Signal Processing Toolbox
blackman	Signal Processing Toolbox
boxcar	Signal Processing Toolbox
chebwin	Signal Processing Toolbox
hamming	Signal Processing Toolbox
hann	Signal Processing Toolbox
kaiser	Signal Processing Toolbox
triang	Signal Processing Toolbox

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