A short addendum on the RKW-1. It turns out that merely observing the speaker state at a series of instants clocked to Voltage Modular’s 48kHz sample rate introduces aliasing. This happens because we’re shifting the points in time at which sharp transitions occur in the output, which generates upper harmonics that aren’t there in the source signal and which start to fold back past the Nyquist frequency, adding metallic aliasing. It’s extra colour, sure, but it isn’t the colour we’re looking for.

The original Sinclair ZX Spectrum had strikingly limited sound-generation capabilities: a single piezo beeper, whose value could be set to “on” or “off”, was responsible for every kind of noise the computer could make, from bleeps and blips to its distinctive tape loading signal. There was no dedicated sound chip: all control over the bleeper had to come from the central CPU, which meant that it had to be interleaved with whatever else that CPU might be doing, like executing game logic or updating the display. This gave rise to some formidable programming challenges which, in the usual way of Spectrum game development, in turn gave rise to formidable ingenuity.

Phantasmatic is another new module for Cherry Audio’s Voltage Modular. Like its older brother Prismatic, it uses phase distortion to shape waveforms by changing the way the phase accumulator moves through a wavetable.

Where Prismatic uses an 8-bit processing path, with small lookup tables and fixed-point arithmetic running at a 16Khz sample rate, Phantasmatic runs at 48Khz and uses double precision floating point arithmetic throughout. This eliminates most of the soft (and occasionally harsh) digital noise that blankets Prismatic’s output, yielding a cleaner but slightly less characterful sound. It also cleans up a lot of aliasing, especially with the 2x oversampling anti-aliasing filter engaged (controlled via a “niceness” switch, where Prismatic had a “nastiness” switch for making the sound worse).