The BD909 is a kick-drum generator using a clone of the Roland TR-909 circuit.It also adds non-original controls to create a kick with a punch in the low-low-range (BD808 is also a lower-end).
Attack, Decay, Tune Decay, Accent, and Level-based controls added Tune's control, an uteneated CV control, and Tune's attack.The width of Tune Decay is also wider, and it is possible to find a sweet spot with a different sound than the original 909.In addition, a disttion and its CV control have been added to overload the waveform.
It starts with a classic 909 sound and allows you to use the additional function above to change the sound more flexibly so that you can create a wide kicksound.