Yes, probabilities can be set. For instance, we get the 16th silences 30% of the time, in each instrument part (regardless of the pool size).
]]>I wish I had access to a more powerful programming language to refine the lead algorithm.
Bintracker is literally a Scheme interpreter, so you can pretty much do anything with it. It's very much unfinished at the moment, but source is available if you're feeling lucky 
My random pools, for a given chord:
bass: 16th notes and 16th silence, fundamentals and fifths, with a fixed first note
percussion: fixed kick and snare, random treble 16th hits and 16th silences
arpeggios: only 16th in random order
high counter-melody: fixed notes (one per chord)
lead: 16th, 8th and dotted 8th notes, generally fundamental, second, third, sometimes fifth, and 16th silences
I wish I had access to a more powerful programming language to refine the lead algorithm.
Concerning harmonic pattern, there's a lot of possibilities, I used my musical knowledge and instinct to decide which are the correct ones. In any cases, it's an 8 bars pattern that starts with Cm and finishes with G (exept the bridge, which starts with Ab). You will see the possible patterns on the video.
]]>EDIT: now it has it's one webpage http://chiptunegenerator.com/
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