Vocoders are complex machines but working with a simple principle. They take two inputs, put them through filterbanks and apply the envelopes of one input and applies it on the amplitude of the other. Thus the frequency spectrum of one signal is imparted on the other but only if that signal contains those frequencies. Usually vocoders sport filterbanks with at least 10 filters in each, expensive if you want to do it with a modular. This demo shows that you can make quite an efficient vocoding style effect using just one filter each for carrier and modulator!