Figure 9.13 shows how a bandpass filter can be made using a lowpass filter together with modulation. The input spectrum is frequency-shifted by , lowpass filtered, then frequency-shifted by , thereby creating a bandpass filter centered at frequency . From our experience with rectangular-window transforms (Fig.9.11 being one example), we can say that the bandpass-filter bandwidth is equal to the main-lobe width of the aliased sinc function, or radians per sample (measured from zero-crossing to zero-crossing).
Uniform Running-Sum Filter Banks
Modulation by a Complex Sinusoid