Synchronous filtering

A new filtering paradigm is introduced, called synchronous filtering, which notably includes complex or polyphase filters as a subset. The theory introduced demonstrates how a given time invariant filter can be implemented using a combination of modulators and a core filter, which itself could be time varying. That the equivalent synchronous filter processes the identical time-domain complete response as the original is also proven. Sub- and superheterodyne, as well as higher order, filters are discussed. Finally, a companding polyphase filter is introduced for the first time as another instance of a synchronous filter