Why windowing is used in fir filter design?

Windowing is used in FIR filter design to control the frequency response of the filter and to manage the effects of truncating an ideal infinite impulse response. By applying a window function to the filter coefficients, designers can reduce side lobe levels in the filter's frequency response, minimizing artifacts like ripples. This technique also helps in achieving a smoother transition band and better overall filter performance while maintaining the desired characteristics of the filter. Overall, windowing enhances the filter's practical implementation by balancing trade-offs between selectivity and passband ripple.