It sounds to me like a layered kick drum underneath a 808 or like a low sine wave. Its using the attack of the kick drum and the sustain of the 808. of course there is a filter (second song) every 4/8 bars or so. You can do this by just layering the two. Sounds like there is a little distortion on the 808 as well and they chopped off some of the higher frequencies from the 808. That my guess I apologize if my terminology is wrong I hope it makes sense. What program are you using though