Electro-Harmonix Nano Q-Tron Envelope Controlled FilterMaker: Electro Harmonix Model: Nano Q Tron Condition: New Description: Envelope controlled filter is an effect type that ventures beyond the mainstream yet is equally at home in a wide range of genres and equally effective on guitar, bass, keys, horns and more. Electro Harmonix is a pioneer in this effect category and has been making envelope controlled filter pedals since the 1970s! The Nano Q Tron springboards off that deep heritage. Heres how it