Voice cards expand the functionality of the Bullfrog and make it even more versatile. Some voice cards replace patch cables - they connect the "modules* of the Bullfrog internally, while others have built-in mixers, signal generators, and advanced electrical circuits to control the synthesizer, for example, the Sequencer sends CV to control pitch and gate to start events on the synthesizer and the Sampler/Looper emulates reel to reel tape recorder functionality

The ADSR voice card adds a full four-stage attack/decay/sustain/release envelope that can be triggered by the Bullfrog's GATE button (or notes played on a connected MIDI keyboard). It is internally routed to the VCA once connected and features a RELEASE CV input, as well as a seperate OUTPUT to get another copy of the ADSR envelope that can be patched elsewhere.