Obtaining Narrow Transition Region in STFT Domain Processing Using Subband Filters

The short-time Fourier transform (STFT) and the inverse short-time Fourier transform are often used in signal analysis, modification, and synthesis. In this work, we focus on the effect of overlapping STFT subbands in relation to signal modification and synthesis. We illustrate that the subband overlapping can impose a negative mixing effect on STFT domain signal processing such as bandlimited frequency shifting. We propose a subband filtering method, by using subband low-pass and high-pass filters in the affected frequency region, to reduce the mixing effect locally without changing the general STFT processing. We show in simulation experiments that our subband filtering method is efficient; the bandwidth of the affected frequency region is typically reduced by a factor of 2-3, and there is significantly less signal distortion in the affected frequency region.