Synthesizer

An electronic instrument that generates sound from scratch — typically oscillators for tone, filters to shape harmonics, and envelopes/LFOs for movement — as opposed to recording or reproducing an existing sound. This spoke’s founding instruments are all synthesizers or their raw ingredients.

Axes that keep recurring

• Analog vs digital. filtopia and the test-equipment scene argue for the all-analog signal path on tone grounds (“better sine waves”); polyuanalog hedges with DCOs (digital control of analog oscillators) for tuning stability; gr-mega is fully digital/DSP, its whole premise (granular-synthesis) impossible in analog. The analog-vs-digital sound argument is a live tension — see synthesis.
• Synthesis method. Not only subtractive analog: gr-mega is granular (grain-cloud resynthesis of sampled audio), one of several sample-mangling engines — see granular-synthesis.
• Mono vs poly. filtopia is monophonic (one note, maximum voice complexity); polyuanalog scales to ~120 voices via its conductor–voice design; cyma-forma-alt runs five oscillators tuned to soundscapes rather than to a keyboard.
• Finished vs build-it-yourself. A hand-built commercial flagship (filtopia, £1,799, 200 units) vs an open-source repo you assemble and flash (polyuanalog, MIT).
• The filter as identity. How a synth filters is often what defines it, and the two all-analog flagships bet oppositely: filtopia wires five filters in parallel (formant timbres), while cyma-forma-alt stacks two MS-20-style multimode filters in series. See modular-routing.
• How you play it. Beyond keys: cyma-forma-alt adds sensor control — a microphone (“ears”) and light sensors (“eyes”, theremin-style) — so the environment drives the instrument.
• Tuning. Not always 12-tone equal temperament: cyma-forma-alt builds in 14 scales including just intonation, making microtuning a first-class feature.

Edges

The test-equipment practice sits just outside the category: a bare oscillator or signal generator is a synth’s tone source without the instrument built around it. Distinct from the sound-reproduction chain (speakers/enclosures) owned by loudspeaker-design-wiki — a synth makes the signal; a loudspeaker plays it back.