Sounds like a saw-tooth layered with a square or a sine wave oscilator, about one octave lower, with two different envelope modulators, and a little bit of reverb.

The first envelope, responsible for the amplitude of the saw-tooth, has a fast attack and a short sustain/decay setting. The second envelope also has a fast attack but a high sustain and decay.

It sounds like the filters are fairly open/or are only affecting the sine/square wave.

That's just my guess. If I get a chance, I may try to get a proof up, later.