as far as I understand the bins arent 'empty', they just have zero mag or close to zero; there will be leakage to other bins due to artefacts of the windowing of the signal, anyway, which will give the theoretically zero mag bins a mag value. Phase is completely independent of mag, and I think it probably needs to be kept track of in this application, even if the mag is zero for a particular frame-- I think you need to use framedelta, phaserap and frameaccum to do this
Thanks Terry. I'll try it out. I had presumed that I wouldn't need framedelta/phasewrap/frameaccum for convolution purposes. But I can kind of see that something has to be done with the phase in this case.