CPU Micron

CPU Micron is a schematic-accurate recreation of the analogue synthesiser voice Roland built into the MC-202 in 1983, made for iPad by Central Processing Unit.

Rather than approximating the sound by ear, its DSP is built from the original circuit diagram and the real component values: the CEM3340 oscillator, the IR3109 transconductance filter, the discrete-transistor envelope and the op-amp LFO. Every figure comes from the schematic, from a measurement of a working hardware unit, or from the manufacturer's own service-manual specifications — and where a figure could be both calculated and measured, the two agree.

THE VOICE
• Oscillator with simultaneous saw and pulse, variable pulse width and PWM, and a 2′ to 16′ footage switch
• Sub oscillator one and two octaves down
• Four-pole low-pass filter that self-oscillates into a clean sine at the top of the control, reproduced from the real feedback path
• Discrete ADSR envelope on its real RC time constants, and a triangle LFO with rate and fade-in delay
• TUNE, PORTAMENTO, ACCENT, VOLUME and TEMPO, on a hardware-exact panel

THE SEQUENCER
Reconstructed from the original owner's manual rather than replaced with a step grid: two channels, gate time as a fraction of step time, bars stored as data, and the machine's own key map. A sequence can be written to an audio file and played into the hardware's tape input, or read back from tapes the machine itself recorded - notes, accents, glides, ties and bar lines intact.

AND EVERYTHING 1983 LACKED
• Patch and sequence memory, with factory banks of basses, leads and effects
• Presets and sequences kept in the Files app, so they can be backed up, shared and moved between devices
• Two randomisers, one for patches and one for sequences, that write something worth keeping
• MIDI CC on every panel control
• Five panel finishes
• The full manual, built in

For iPad, in landscape. No account, no subscription, no network.