Synthesizer Fundamentals

This document explains the core concepts of sound synthesis used in Relanote.

What is a Synthesizer?

A synthesizer is an electronic instrument that generates sound from scratch using electrical signals. Unlike acoustic instruments that produce sound through physical vibration, synthesizers create sound mathematically.

The Physics of Sound

Sound Waves

Sound is a pressure wave traveling through air. We perceive:

• Frequency (pitch): How fast the wave oscillates (Hz = cycles per second)
• Amplitude (volume): How much pressure change
• Timbre (tone color): The wave's shape

Harmonics and Timbre

Real sounds contain multiple frequencies called harmonics or overtones:

Harmonic series for a 100 Hz fundamental:

Harmonic	Frequency	Interval from Fundamental
1st	100 Hz	Fundamental (root)
2nd	200 Hz	Octave (P8)
3rd	300 Hz	Octave + Fifth (P8 + P5)
4th	400 Hz	Two octaves (P15)
5th	500 Hz	Two octaves + Major 3rd
6th	600 Hz	Two octaves + Fifth
7th	700 Hz	Slightly flat minor 7th
8th	800 Hz	Three octaves
...	...	...

The relative strength of these harmonics determines timbre - why a piano sounds different from a violin playing the same note.

Oscillators

What is an Oscillator?

An oscillator generates a repeating waveform at a specific frequency. It's the sound source - the starting point of synthesis.

Waveform Types

Each waveform has unique characteristics:

Waveform	Harmonics	Sound	Example Use
Sine	Fundamental only	Pure, flute-like	Sub-bass, pure tones
Square	Odd (1, 3, 5...)	Hollow, clarinet-like	Video games, leads
Sawtooth	All (1, 2, 3...)	Bright, brassy	Strings, brass, leads
Triangle	Odd (weak)	Soft, mellow	Woodwinds, flutes
Pulse	Variable	Nasal, thin	8-bit, chiptune
Noise	All (random)	Hiss, breath	Hi-hats, percussion

; Different oscillator examples
synth PureTone = { osc: Sine, env: envelope 0.01 0.1 0.8 0.3 }
synth Clarinet = { osc: Square, env: envelope 0.08 0.2 0.7 0.2, filter: LowPass 2000 0.3 }
synth BrightLead = { osc: Saw, env: envelope 0.01 0.15 0.7 0.2, filter: LowPass 4000 0.5 }
synth GameBoy = { osc: Pulse 0.125, env: envelope 0.001 0.1 0.5 0.1 }
synth HiHat = { osc: Noise, env: envelope 0.001 0.05 0.0 0.05, filter: HighPass 8000 0.5 }

Combining Oscillators

Relanote allows mixing multiple oscillators for richer sounds:

synth RichPad = {
  osc: (Saw |> mix 0.4) +
       (Square |> mix 0.3) +
       (Sine |> mix 0.3 |> octave -1),
  env: envelope 0.5 0.3 0.7 1.0,
  filter: LowPass 3000 0.2
}

Detuning

Slightly detuning oscillators creates a thick, chorusing effect:

synth SuperSaw = {
  osc: (Saw |> mix 0.33) +
       (Saw |> mix 0.33 |> osc_detune -12) +
       (Saw |> mix 0.34 |> osc_detune 12),
  env: envelope 0.01 0.2 0.8 0.3,
  detune: 7
}

Envelopes

What is an Envelope?

An envelope shapes how a parameter changes over time. The most common is the amplitude envelope (ADSR), which controls volume.

ADSR Envelope

Parameter Ranges

Parameter	Range	Description
Attack	0 - 10 sec	Time to reach peak
Decay	0 - 10 sec	Time to reach sustain
Sustain	0 - 1.0	Level (not time!)
Release	0 - 10 sec	Time to silence

Envelope Shapes for Different Sounds

; Piano-style
synth Piano = {
  osc: (Sine |> mix 0.6) + (Triangle |> mix 0.4),
  env: envelope 0.005 0.4 0.3 0.8
}

; Pluck-style
synth Pluck = {
  osc: Saw,
  env: envelope 0.001 0.15 0.0 0.1
}

; Pad-style
synth Pad = {
  osc: (Saw |> mix 0.5) + (Square |> mix 0.5),
  env: envelope 0.5 0.3 0.7 1.0,
  filter: LowPass 2000 0.2
}

; Organ-style
synth Organ = {
  osc: (Sine |> mix 0.5) + (Sine |> mix 0.3 |> octave 1) + (Sine |> mix 0.2 |> octave 2),
  env: envelope 0.01 0.0 1.0 0.1
}

Pitch Envelope

A pitch envelope changes frequency over time. Essential for drum synthesis:

synth Kick = {
  osc: Sine,
  env: envelope 0.001 0.15 0.0 0.1,
  pitch_env: (150, 40, 0.08)  ; start, end, time
}

Filters

What is a Filter?

A filter removes or reduces certain frequencies from a sound. Filters are essential for shaping timbre.

Filter Types

Low-Pass Filter (LPF)

Passes frequencies below the cutoff, removes frequencies above. This is the most common filter in synthesis - it creates darker, warmer sounds from bright sources.

synth WarmBass = {
  osc: Saw,
  env: envelope 0.01 0.1 0.6 0.2,
  filter: LowPass 400 0.4
}

High-Pass Filter (HPF)

Passes frequencies above the cutoff, removes frequencies below. Used for hi-hats and removing bass from instruments.

synth HiHat = {
  osc: Noise,
  env: envelope 0.001 0.05 0.0 0.05,
  filter: HighPass 8000 0.5
}

Band-Pass Filter (BPF)

Passes frequencies around the center frequency, removes both above and below. Creates "telephone" or "radio" effects.

Resonance (Q)

Resonance boosts frequencies near the cutoff:

; Low resonance - natural
synth Natural = {
  osc: Saw,
  filter: LowPass 2000 0.2
}

; High resonance - squelchy acid bass
synth Acid = {
  osc: Saw,
  filter: LowPass 800 0.8,
  env: envelope 0.001 0.1 0.4 0.1
}

Filter Cutoff and Brightness

Modulation

What is Modulation?

Modulation means using one signal to control another. It creates movement and interest in sounds.

LFO (Low Frequency Oscillator)

An oscillator running at sub-audio rates (0.1 - 20 Hz) to modulate parameters:

Common LFO destinations:

• Pitch → Vibrato
• Filter cutoff → Wah effect
• Amplitude → Tremolo
• Pan → Auto-pan

Velocity

MIDI velocity (how hard you hit a key) can modulate:

• Volume (louder with harder hits)
• Filter cutoff (brighter with harder hits)
• Attack time (faster attack with harder hits)

Practical Sound Design

Bass Sounds

; Sub bass - pure low end
synth SubBass = {
  osc: Sine,
  env: envelope 0.01 0.1 0.8 0.2,
  filter: LowPass 200 0.2
}

; Synth bass - fuller
synth SynthBass = {
  osc: (Saw |> mix 0.6) + (Square |> mix 0.4),
  env: envelope 0.01 0.15 0.5 0.15,
  filter: LowPass 600 0.5
}

; Acid bass - squelchy
synth AcidBass = {
  osc: Saw,
  env: envelope 0.001 0.1 0.3 0.1,
  filter: LowPass 400 0.85
}

Lead Sounds

; Classic lead
synth Lead = {
  osc: Saw,
  env: envelope 0.01 0.1 0.7 0.2,
  filter: LowPass 4000 0.4,
  detune: 5
}

; Supersaw lead (trance)
synth SuperSaw = {
  osc: (Saw |> mix 0.33) +
       (Saw |> mix 0.33 |> osc_detune -12) +
       (Saw |> mix 0.34 |> osc_detune 12),
  env: envelope 0.01 0.2 0.8 0.3,
  filter: LowPass 6000 0.3,
  detune: 7
}

Pad Sounds

; Warm pad
synth WarmPad = {
  osc: (Saw |> mix 0.4) + (Triangle |> mix 0.6),
  env: envelope 0.8 0.4 0.6 1.5,
  filter: LowPass 2500 0.2,
  detune: 8
}

; String pad
synth StringPad = {
  osc: (Saw |> mix 0.5) + (Saw |> mix 0.5 |> osc_detune 5),
  env: envelope 0.4 0.3 0.7 1.0,
  filter: LowPass 4000 0.3
}

Drum Sounds

; Kick drum - pitch envelope is key
synth Kick = {
  osc: Sine,
  env: envelope 0.001 0.15 0.0 0.1,
  pitch_env: (150, 40, 0.08)
}

; Snare - noise + tone
synth Snare = {
  osc: (Triangle |> mix 0.4) + (Noise |> mix 0.6),
  env: envelope 0.001 0.1 0.0 0.1,
  filter: HighPass 200 0.3
}

; Hi-hat - filtered noise
synth HiHat = {
  osc: Noise,
  env: envelope 0.001 0.05 0.0 0.05,
  filter: HighPass 8000 0.6
}

Summary

Further Reading

• Sound Synthesis: Detailed WebAudio implementation
• Preset Reference: Complete list of built-in presets
• Music Theory: The musical concepts behind synthesis