Subtractive Synth

It starts with a shape

Every note begins as an oscillator — a circuit that swings back and forth at some frequency. Play an A and it swings 440 times a second. But how it swings decides the timbre, and that's the first thing to try above: flip between the four waveforms while holding a key and watch the oscilloscope.

A sine is the purest possible tone — a single frequency, one clean curve, nothing else. It sounds soft and flute-like, almost boring. A sawtooth looks like a shark's fin and sounds bright and buzzy, because that ramp shape is secretly a whole stack of frequencies at once: the fundamental plus every harmonic above it, piled up. The square is hollow and reedy (odd harmonics only); the triangle sits in between, mellow but with a little edge. The spectrum on the rightunder the oscilloscope is the giveaway — the sine shows one lonely bar, the sawtooth shows a comb of them marching off toward the high end. Bright literally means more harmonics.

Subtractive synthesis: carving with a filter

So a sawtooth hands you far too much — a rich, harsh spray of harmonics. The trick of subtractive synthesis is to start with that surplus and take away what you don't want. The tool is a lowpass filter: it lets low frequencies pass through and progressively muffles everything above a chosen cutoff frequency.

Hold a bright sawtooth and slowly drag the Cutoff slider down. You'll hear the sound go from buzzy to warm to muffled, and on the spectrum you'll literally watch the tall forest of high harmonics get mowed down from the right — the dashed line marks where the filter starts cutting. That single knob is the most expressive control on the whole instrument. It's the "wah" in a wah pedal and the slow bloom at the start of a thousand dance tracks.

Resonance: a spotlight at the cutoff

Turn up Resonance and the filter stops being polite. Instead of a gentle roll-off, it boosts the frequencies right at the cutoff point, creating a sharp peak — you can see it as a little spike travelling along the spectrum as you sweep the cutoff. Crank it far enough and the filter nearly whistles on its own. Resonance is what gives acid basslines their squelch and vocal-ish synths their "ee"/"oo" vowels: you're emphasizing one narrow band and sweeping it around.

ADSR: the shape of loudness over time

A real note isn't just on or off. Pluck a string and it's loud instantly, then fades. Bow it and the sound swells in. That envelope of loudness over time has four stages — Attack (how fast it reaches full volume), Decay (how fast it drops to a holding level), Sustain (that holding level, for as long as you keep the key down), and Release (how long the tail rings out after you let go).

Short attack and zero sustain give you a percussive pluck. Long attack and long release give you a pad that breathes in and hangs in the air. Set Attack to its slowest and hold a chord — the notes fade in like a sunrise instead of stabbing at you. Nothing about the frequencies changed; only their volume over time did, and it completely transforms the feel.

Reverb: putting it in a room

The last stage answers a simple question: where is this sound happening? Dry, in a padded booth, or at the far end of a cathedral? The Space knob feeds the signal through a reverb — thousands of tiny reflections, generated here on the fly as a decaying burst of noise — so the note keeps ringing after it should have stopped. A touch adds depth; a lot turns even a short pluck into a slow, cavernous wash.

That's the whole chain: a shape, carved by a filter, shaped by an envelope, placed in a room. Every patch on every synth is some recipe of those four moves. Now go make a few of your own.