The Stereo Talking Machine with Vocal Formant Filter from Electro-Harmonix is a customizable envelope-controlled digital vowel filter. The Stereo Talking Machine (STM) utilizes multiple moving filters allows your guitar to create growling, gurgling, and snarling sounds. Nine selectable Voices deliver vowel sounds such as AH-OO and OW-EE, as well as Bassballs and wah-type dynamic filters. The Voices can be shaped with individual Attack and Decay controls while Sensitivity adjusts the envelope response. The resulting effects mimic characteristics of human speech and create sounds that are both organic and harmonically rich. The Stereo Talking Machine possesses true stereo outputs as well as an Effects Loop. An Expression Pedal input provides real time control over filter sweeps, while nine preset locations let you store and recall your selected programs. Each voice option in the STM sweeps between two distinct filter settings, mimicking the way a human mouth moves to form particular vowel sounds. The direction of the filter sweep can be reversed using the Sensitivity knob. The WAH and BB voice options simulate a classic wah-wah pedal filter and the EHX Bassballs filter respectively.