I don't have an Mbase, but I do have an xbase 888, and I suspect it will probably work the same.
I read the manual pretty recently, but since it's usually better to be check yourself than to guess, I did a quick google and had a look in the manual from the jomox site online, just to be sure.
Here's the 2 parts that are important for you :
3.2. Pitch < 000-255 >
This parameter determines the basic pitch of the bass drum. Sub
basses down to 10 Hz or relatively high tones are possible. Don't
mistake this with the Tune parameter. With most kinds of
instruments this parameter is called "tune", but because everybody
knows the 909 and its specific tune, we called it pitch.
4.3. Pitch Mode < Lin / SEM >
<Lin> The bass drum pitch (the VCO frequency) is output as a linear
frequency over the keyboard in Split Mode 2 (see above).
<SEM> The bass drum pitch (the VCO frequency) is output in
musical semitone intervals over the keyboard. The usable range is
approximately 3 octaves. So it is possible to turn the MBase11 into a
little bass synthesizer, if you turn tune low and decay long. The long
decaying tone can now be played in melodies.
no offence mate, but "I've lost my manual I think".
just check the net.