The Lumitron Resonant Filter is an adaptation of the Musitronics Mu-tron III, designed by Mike Biegel and originally released in 1972.
The Mu-tron III was the very first commercial envelope filter pedal, also called an autowah, using optocouplers to dynamically control a series of frequency filters based on the level of the input signal. The vocal-like effect was quickly embraced by musicians and soon became a characteristic effect of entire genres, particularly funk. Notable Mu-tron III users include Bootsy Collins on bass, Jerry Garcia on guitar, and even Stevie Wonder, who used it on a Clavinet.
Musitronics was sold to ARP in 1979, who produced the pedals until 1980. Mike Biegel later contracted with Electro-Harmonix to release an updated version of the circuit in 1995, called the Q-Tron, as well as the Bi-Filter rack unit with expanded features. The original Q-Tron was later adapted as the Mini Q-Tron, Micro Q-Tron, and Q-Tron+, the latter two of which are still in production.
In 2019, the Mu-tron brand was resurrected with Mike Biegel once again designing new effects. The Micro-Tron IV is an updated version of the Mu-tron III, with modernized circuitry, CV input and output, and swappable optical modules for different reaction times and filter characteristics.
The Lovetone Meatball (available as our Spectron project) was based on the Mu-tron III with a greatly expanded feature set. If you wish the Lumitron had a lot more knobs and switches, it’s worth a look.