A synthesis technique which involves computing a spectral profile of an input signal via Fourier transform, constructing a complex filter which fits this spectrum, and then using the filter to impose the spectral characteristics on a second input signal. The first synthesizers to use resynthesis, in a crude form, were vocoders. These used a set of bandpass filters, usually 10 or so, to measure the spectral content of an input voice signal (or some other signal), and then used a second set of bandpass filters, which tracked the output levels of the first set, to filter a second input signal. Even the relatively crude vocoders of the 1970s were renown for their ability to impose recognizable speech on conventional synth waveforms such as pulse waves and triangle waves.
Resynthesis has not been much explored in commercially produced synthesizers or software. One of the few to do so was the Hartmann Neuron.