The synthesizer, knob by knob

Almost every synth you will meet, from a Roland SH-101 to a free plugin, follows the same plan, called subtractive synthesis: start with a harmonically rich wave, carve some of it away with a filter, then shape its volume over time.

Subtractive synth signal flow Oscillator feeds filter, filter feeds amplifier, amplifier feeds effects. Envelope 1 controls the filter cutoff, envelope 2 controls the amplifier, and the LFO can modulate pitch, cutoff or volume.

Oscillators make the raw sound

The oscillator produces the waveform from lesson 1 at the pitch of the key you press. Most synths give you two or more. Useful moves:

• Detune: tune a second oscillator a few cents (hundredths of a semitone) away from the first. The two drift in and out of phase and the sound thickens. Two detuned saws are the start of every lush chord.
• Octave: put the second oscillator an octave up for brightness or down for weight.
• Sub oscillator: a sine or square one octave below. Instant bass weight.
• Noise: random hiss, the raw material for hats, snares, breath and wind.

The filter shapes brightness

The filter removes harmonics, which is where the word subtractive comes from.

• Low-pass lets lows through and cuts highs. Turn the cutoff down and the sound gets darker and rounder. You will use this 90% of the time.
• High-pass cuts lows. Use it to thin chords and skanks so they don't fight the bass.
• Band-pass keeps a slice in the middle: telephone-like and focused, ideal for a reggae skank or a rim click.
• Resonance (also called Q or emphasis) boosts the frequencies right at the cutoff. A little adds character; a lot gives the squelchy whistle of acid house and Plastikman.

Envelopes shape a sound over time

An envelope is a shape that plays out every time you press a key. The classic one has four stages, ADSR:

• Attack: how long the sound takes to rise from silence to full level.
• Decay: how long it takes to fall from the peak to the sustain level.
• Sustain: the level it holds while you keep the key down. Sustain is a level, not a time, which confuses everybody at first.
• Release: how long it takes to fade out after you let go.

Most synths have two envelopes. The amp envelope controls volume. The filter envelope opens and closes the cutoff, and its amount knob says how far. A fast filter envelope with zero sustain makes a pluck; push the resonance and it becomes an acid line. Learn these four shapes and you can build most sounds in this course:

The LFO adds movement

A low-frequency oscillator is an oscillator too slow to hear, usually 0.1 to 20 cycles per second. Instead of making sound, it moves a knob. On pitch it gives vibrato; on volume, tremolo; on the filter cutoff, a wobble. Sync the LFO rate to the tempo and the movement locks to the groove.

Other kinds of synthesis worth knowing

FM synthesis (the Yamaha DX7, Elektron Digitone, the free plugin Dexed) makes one oscillator wobble the pitch of another at audio speed. It gives bells, metallic hits and the glassy blips that minimal techno loves. Wavetable synthesis (Serum, Vital) scans through a stack of waveforms for evolving tones. Sampling plays recordings; digital cumbia is built largely from sampled percussion and accordion. You do not need these yet. Subtractive covers everything in this course.

Synth Lab

Two oscillators, filter, two envelopes, LFO, drive, delay and reverb, with 18 preset sounds. It plays on your device once the page has loaded.

Synth bass: the subtractive voice

Most minimal and dub basslines are one subtractive synth voice. An oscillator makes a raw, harmonically rich wave. A low-pass filter removes everything above its cutoff. An amplifier shapes the volume. An envelope opens the filter at the start of each note and lets it close, which is what makes a note go "bwow" instead of "bzzz."

Resonance boosts the frequencies right at the cutoff. A little makes the bass rubbery. A lot makes it squelch and whistle. In minimal the filter is often the melody: the notes barely change while cutoff, decay and resonance get ridden for minutes. The LFO here does that riding for you, sweeping the cutoff over a set number of bars.

Waveform

Saw is bright and buzzy, square is hollow, sine is pure sub.

Env amount

How far the filter opens on each note.

Decay

How fast it closes again. Short is a pluck, long is a swell.

Glide

How long a slide step takes to bend into its note.

Note length

Short stabs or held tones.

Bass synth

A 16-step bassline on one subtractive voice, with accent, slide and an LFO on the cutoff. It plays on your device once the page has loaded.