an oto guide · by ear nº3

Synthesis, by ear

Four ideas turn electricity into an instrument: an oscillator makes a tone, a filter shapes its color, an envelope gives it a life span, and an LFO makes it move. You will learn all four by playing them. Start here.

What you just heard is a raw sawtooth wave. Bright, buzzy, a little rude. Everything below is about taming it.

01

The oscillator

source

An oscillator is a machine that repeats a shape. Pick a shape, pick how many times per second it repeats, and you have a tone. The repeat rate is the pitch. The shape is the color.

There are four classic shapes, and each has its own character because each contains a different recipe of harmonics. A sine is one pure frequency and nothing else. A triangle adds a few soft overtones. A square adds only the odd harmonics, which gives it a hollow, woody sound. A sawtooth contains every harmonic, which is why it sounds the brightest and the buzziest. That brightness is not a flaw. It is raw material. Subtractive synthesis means starting with too much and carving away.

Try this. Hold the pad below and cycle through the four shapes without letting go. Do not look at the names. Just notice: which one sounds like a flute? Which one sounds like an old video game? Which one sounds like a string section waiting to happen?
rig 01 · shape and pitch
220 Hz
The screen shows the actual wave leaving your speakers. Watch the corners: sharp corners mean bright sound. That is the whole spectrum chapter in one sentence.
02

The filter

subtract

A low pass filter lets the lows pass and turns the highs down. One knob, called cutoff, decides where the ceiling sits. Sweep it down and a bright saw turns warm, then muffled, then almost pure. You are not adding anything. You are subtracting. This is the move the whole genre is named after.

The second knob is resonance. It boosts a narrow band right at the cutoff point, so the filter stops being a polite ceiling and starts having an opinion. A little resonance adds presence. A lot makes the filter whistle at its own cutoff frequency, and if you sweep the cutoff while it whistles, the filter starts to sing. That singing filter, swept by hand on a cheap silver box called the TB 303, accidentally invented acid house.

Try this. Start the drone. Sweep cutoff slowly from right to left and listen to the harmonics leave one by one, top down. Then set resonance high, around 18, and sweep again. Same knob, completely different instrument.
rig 02 · carve the drone
2340 Hz
2
The screen shows the live spectrum: frequency left to right, loudness as height. Watch the cliff edge move as you sweep, and watch a peak grow at the edge as you raise resonance.
03

The envelope

shape in time

Everything so far drones. Real notes are born, they live, and they die. The envelope is the shape of that life, drawn as loudness over time, and it has four stages: attack, decay, sustain, release. ADSR.

Attack is how long the note takes to reach full volume after you press the key. Decay is how long it takes to fall from that peak to its resting level. Sustain is that resting level, the loudness while you hold the key. Release is how long the sound takes to fade after you let go. Four numbers, and they are the difference between a drum and a violin. A pluck is instant attack, fast decay, zero sustain: all the energy up front, like a struck string. A pad is the opposite: slow attack, full sustain, long release, a note that breathes in before it speaks and exhales after you leave.

Try this. Tap the trigger with the pluck setting. Then load pad and hold the trigger for a few seconds before letting go. Same oscillator, same filter, same pitch. Only time changed.
rig 03 · give it a life span
3 ms
0.2 s
0%
0.1 s
The drawing is the envelope itself: up the attack, down the decay, along the sustain shelf, out the release. The moving dot is where your note currently is in its life.
04

The LFO

movement

LFO stands for low frequency oscillator. It is the same machine as chapter one, but running so slowly you hear it as movement instead of pitch. It never reaches your speakers. Instead, it turns a knob for you, over and over, perfectly in time.

What it sounds like depends entirely on which knob it grabs. Point it at pitch and the note wavers gently: vibrato, the thing a violinist does with a rocking finger. Point it at the filter cutoff and the brightness pulses open and closed: wah, wobble, the engine of dubstep bass. Point it at volume and the note trembles: tremolo, the shimmer in surf guitar. One slow sine wave, three completely different musical meanings.

Try this. Start the drone with the LFO pointed at the filter. Set the rate around 2 Hz and the depth high. That is the wobble. Now switch the target to pitch, drop the depth low, and raise the rate to 5 or 6 Hz. That is vibrato. Nothing changed except which knob the LFO is holding.
rig 04 · an automated hand
2.0 Hz
60%
The screen shows the LFO wave itself, crawling by at its real speed. Everything you hear moving is this line, translated onto a knob.
05

The playground

all four together

Here is the whole chain in one instrument: oscillator into filter into envelope, with the LFO on call. This is, honestly, most of a Minimoog, a 303, and half the presets you have ever heard. Load a preset, play a note, then open the hood and figure out why it sounds the way it does.

Try this. Load acid, hold a low key, and sweep the cutoff yourself while it plays. Then load wobble bass and listen to the LFO do the same sweep for you, in time. When you can hear the difference between a hand on the knob and an LFO on the knob, you have the whole idea.
rig 05 · the synth
2340 Hz
4
5.0 Hz
0%
4 ms
0.3 s
60%
0.2 s
lfo →
presets

Click and hold the keys, or use your computer keyboard: A S D F G H J K for white keys, W E T Y U for black.

Chords welcome. Hold several keys at once and sweep the cutoff. Congratulations, you are now a string machine.
06

How Oto uses this

Oto is a DJ instrument you talk to. When you tell it to make a transition darker, or let this one breathe, or bring the energy up slowly, it has to translate your words into exactly the moves you just learned.

音 the same four ideas, at set scale

Darker is a filter move. When you ask Oto to darken a blend, it is easing a low pass cutoff down across the outgoing track, the same sweep you did by hand in chapter two, just longer and gentler.

Breathe is an envelope move. A transition that breathes has a slow attack and a long release, at the scale of bars instead of milliseconds. Oto shapes energy over a phrase the way rig 03 shapes a single note.

Movement is an LFO move. Pumping, swelling, and rhythmic filter play are all slow modulation locked to tempo. When Oto adds motion to a loop, it is pointing an LFO at a knob and choosing the rate in beats, not hertz.

This is why we teach synthesis in a DJ guide series. The language you use to direct a set and the physics of a single synth note are the same vocabulary at two zoom levels. Learn it on one note and you can hear it in a whole night.

Oto Labs · keep listening

Continue by ear.

07MIDI, by earSee the messages that connect musical gestures to sound. 01Phrasing, by earFeel beats become bars, phrases, and well-timed transitions.

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