I am trying to work through an issue with an FFT for audio : I have no spectral leakage while playing back audio, but the moment I change or zero out a value in any of the FFT bins, artifacts are introduced.
I have a basic understanding of what causes spectral leakage while working with an FFT : the rectangular window in the time domain constitutes a sinc function which is infinite in length. If a desired tone were to exist at a boundary of two bins, this would create leakage not only in the adjacent bins of the FFT, but further down the line due to the side-lobes of the sinc function.
What I do not understand is the following : if the FFT went through proper pre-windowing and post-windowing such that there is close to no spectral leakage in the signal, how could nulling or changing the value of some of the FFT bins cause spectral leakage? How do I circumvent this issue?