The window design technique for FIR filters involves choosing an ideal frequency-selective filter with the desired passband and stopband characteristics, and then multiplying or "windowing" its infinite impulse response with an appropriate window function to make it causal and finite. This windowing in the time domain corresponds to convolution in the frequency domain. Common window functions are used to truncate the ideal filter response while maintaining desirable filtering properties. MATLAB code can be used to implement windowed FIR filters.

1. FIR Filter Design (Windowing
Technique)
The basic idea behind the window design is to choose a proper
ideal frequency-selective filter (which always has a noncausal,
infinite-duration impulse response) and then to truncate (or
window) its impulse response to obtain a linear-phase and causal
FIR filter.
Therefore the emphasis in this method is on selecting an
appropriate windowing function and an appropriate ideal filter. We
will denote an ideal frequency-selective filter by ,which has
a unity magnitude gain and linear-phase characteristics over its
passband, and zero response over its stopband.
( )j
dH e 

2. The impulse response will be

3. • jjkjjkjkj
This multiplication in time domain implies
convolution in frequency domain. Because it is one
of the properties of DTFT, DFT or Z-Transform

9. Commonly used windows

10. Matlab Implimentation