Envelope filters have never been as popular as wah pedals despite sharing a lot in common. The beauty of an auto wah type setting is the genres it's spawned over the years around it, can you imagine funk and huge artists we know and love without Envelope filters, follows and auto wahs.
The Doctor Q is a smooth envelope filter with the famous funky wah tone. When set right its possible to get different effects depending on whether you play loud or soft. The bass switch lets low frequencies through which is useful when playing bass and the lower guitar strings.