the frequency range of interest. If the input is from a microphone, and not a CV mask or its equivalent, the inverse filter also must have a pole at zero frequency (an integration operation) to account for the radiation characteristic that connects volume velocity with acoustic pressure. Inverse filtering the output of a CV mask retains the level of zero flow, while inverse filtering a microphone signal does not. Inverse filtering depends on the source-filter model and a vocal tract filter that is linear system, however, the source and filter need not be independent. References Speech synthesis