Baba O'Lowrey is inspired by the 'Marimba Repeat' function that was available on certain models of Lowrey electronic organs.
The most famous use of this function was in the 'synth sequencer' intro to Baba O'Riley by The Who.
The module works by splitting an incoming MIDI note stream into two 'Banks' - A & B. Each key within an octave (from C to B) is split into Bank A or Bank B based on the setting of the bank select rocker switches on the right hand side - left for Bank A and right for Bank B. The default setting of the Bank Select rockers matches the hard-wired configuration of the Lowrey organs which featured Marimba Repeat:
Bank A = B, C, C#, F, F#, G
Bank B = D, Eb, E, Ab, A, Bb
All notes held in Bank A are triggered simultaneously by the first pulse of the internal or external clock. Then, all notes held in Bank B are triggered by the next pulse. This repeats for as long as the keys are held down.
The internal clock has a range of 30 BPM up to 160 BPM. The keys held in Bank A and B will sound alternately on every 1/32nd note, giving rise to that characteristic 'trilling' or 'ratcheting' sound. At faster rates, it sounds more like mandolin tremolo. Faster and slower rates than the internal clock can be achieved by connecting an LFO to the EXT CLK input jack.
The SET A and SET B jacks are logic level inputs which control how the module cycles between Bank A and Bank B:
SET A low, SET B low: output will cycle between Bank A and Bank B alternately, every clock pulse.
SET A high, SET B low: output Bank A only on every clock pulse.
SET A low, SET B high: output Bank B only on every clock pulse.
SET A high, SET B high: output currently selected Bank on every clock pulse without advancing to the alternate Bank.
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