Electronic Music 101: Synthesizers

How Synthesizers Work: From Sound Waves to Music

Have you ever wondered how synthesizers create those captivating electronic sounds? From the pulsating basslines of dance music to the atmospheric pads of ambient tracks, synthesizers have defined the sound of modern music. In this interactive guide, we’ll explore how synthesizers work — no programming experience required!

What Is a Synthesizer?

At its core, a synthesizer is an electronic instrument that generates and shapes sound. Unlike acoustic instruments that produce sound through physical vibrations (like guitar strings or drum membranes), synthesizers create sound from scratch using electronic circuits or digital algorithms.

The first commercial synthesizers appeared in the 1960s and were massive, room-filling machines with patch cables connecting different modules. Today, synthesizers come in many forms: hardware instruments, software plugins, or even smartphone apps. Despite their different appearances, all synthesizers work on similar principles.

The Building Blocks of Sound

To understand synthesizers, we first need to understand sound itself. Sound is a pressure wave that travels through air or other materials. When these waves reach our ears, they cause our eardrums to vibrate, which our brain interprets as sound.

Sound has several key properties:

  • Frequency: How many cycles occur per second, measured in Hertz (Hz). We perceive frequency as pitch — higher frequencies sound higher in pitch.
  • Amplitude: The size or intensity of the wave, which we perceive as volume.
  • Timbre: The character or tone color of a sound, determined by its harmonic content.
  • Duration: How long the sound lasts.

Oscillators: The Sound Source

The heart of any synthesizer is the oscillator. An oscillator generates a repeating waveform at a specific frequency. Different waveforms have distinct timbres due to their unique harmonic content:

Let’s try a simple oscillator. Press the Play button to hear a sine wave, then experiment with different waveforms and frequencies:

Notice how each waveform has its own unique sound:

  • Sine wave: The purest tone with no harmonics, just the fundamental frequency. It sounds smooth and pure.
  • Square wave: Contains only odd harmonics, creating a hollow, buzzy tone similar to a clarinet.
  • Sawtooth wave: Contains all harmonics, producing a bright, brassy sound.
  • Triangle wave: Contains odd harmonics that decrease more rapidly than a square wave, resulting in a softer, more mellow sound.

Rich Sounds with Multiple Oscillators

Most synthesizers use multiple oscillators to create richer sounds. By combining slightly detuned oscillators, we can create thicker, more complex tones. This technique, called “unison” or “super saw” in some synthesizers, is crucial for achieving that fat, professional sound.

Try this dual-oscillator synthesizer. The “Detune” slider adjusts how far the second oscillator is tuned away from the first:

When you slightly detune one oscillator from another, you create subtle phase differences that make the sound fuller and more animated. This is similar to how a choir or string section sounds rich compared to a single voice or instrument — slight variations between performers create a more engaging sound.

Shaping Sound Over Time: The ADSR Envelope

Real instruments don’t just start and stop abruptly — they have distinctive ways their sound evolves over time. A piano note attacks quickly then gradually fades, while a violin note can swell slowly.

Synthesizers model these natural dynamics using what’s called an ADSR envelope:

  • Attack: How quickly the sound reaches full volume
  • Decay: How quickly it falls to the sustain level
  • Sustain: The volume level maintained while a key is held
  • Release: How quickly the sound fades after release

The envelope shapes the amplitude (volume) of the sound over time:

Try adjusting these parameters and listen to how they affect the sound:

  • Short attack, decay, and release with low sustain: Percussive sounds like plucked strings or drums
  • Long attack, medium decay, high sustain, medium release: Pad sounds or strings
  • Short attack, long decay, medium sustain, long release: Piano-like sounds

Filters: Sculpting the Frequency Spectrum

Once we have a raw sound from our oscillators, we can sculpt its frequency content using filters. Filters selectively remove or emphasize certain frequencies, dramatically changing the character of the sound.

The most common filter types are:

  • Low-pass filter: Allows frequencies below the cutoff point to pass through while reducing higher frequencies
  • High-pass filter: Allows frequencies above the cutoff point to pass through, removing lower frequencies
  • Band-pass filter: Allows a band of frequencies to pass through, attenuating frequencies both above and below
  • Notch filter: Removes a band of frequencies while letting all others pass through

Try this filter demonstration. The “Cutoff” knob controls which frequencies are affected, while “Resonance” creates emphasis around the cutoff frequency:

Filters are essential for creating classic synthesizer sounds:

  • Sweeping a low-pass filter with high resonance creates the classic “wah” effect heard in electronic dance music
  • High-pass filters can remove rumble or make sounds thinner and airier
  • Band-pass filters can create telephone-like or nasal qualities

Adding Movement: LFO (Low-Frequency Oscillator)

Static sounds can be boring. Synthesizers use LFOs (Low-Frequency Oscillators) to add movement and evolution to sounds. LFOs are oscillators that operate at very low frequencies, typically below 20 Hz, which is below the range of human hearing.

Instead of producing audible sound, LFOs modulate (change over time) other parameters like pitch, filter cutoff, or volume:

Common LFO applications include:

  • Vibrato: When an LFO modulates pitch
  • Tremolo: When an LFO modulates volume
  • Filter wobble: When an LFO modulates filter cutoff (popular in dubstep)
  • Auto-panning: When an LFO modulates stereo position

The LFO rate controls how fast the modulation happens, while the amount determines how dramatic the effect is.

Putting It All Together

A complete synthesizer combines all these elements into a powerful sound design tool. Here’s a more comprehensive synthesizer with all the components we’ve explored:

With this synthesizer, you can:

  1. Choose from different waveforms for the oscillators
  2. Adjust the balance and detuning between oscillators
  3. Shape the sound over time with the ADSR envelope
  4. Sculpt the frequency content with filters
  5. Add movement with the LFO

Common Synthesis Techniques

Now that we understand the basic components, let’s look at some common synthesis techniques:

Subtractive Synthesis

The technique we’ve primarily explored is called subtractive synthesis. It starts with harmonically rich waveforms (like sawtooth or square waves) and uses filters to selectively remove (subtract) frequencies. This is the classic approach used in analog synthesizers and remains popular today.

FM Synthesis

Frequency Modulation (FM) synthesis uses one oscillator (the modulator) to modulate the frequency of another oscillator (the carrier). This creates complex, often metallic or bell-like timbres that would be difficult to achieve with subtractive synthesis alone. FM synthesis was popularized by the Yamaha DX7 synthesizer in the 1980s.

Wavetable Synthesis

Wavetable synthesis uses stored waveforms (called wavetables) as the basis for sound generation. By smoothly transitioning between different waveforms, you can create evolving sounds with rich harmonic content. This technique is used in many modern digital synthesizers.

Granular Synthesis

Granular synthesis breaks sounds into tiny fragments called “grains” (typically 1-100ms long) and then reassembles them in various ways. This can create ethereal, textural sounds or dramatically transform existing audio.

Physical Modeling

Physical modeling synthesis uses mathematical models to simulate the physical behavior of instruments. Instead of using oscillators and filters, it models how sound is produced in real instruments — like the vibration of strings or the resonance of tubes.

Famous Synthesizers Through History

Synthesizers have evolved dramatically since their inception. Here are some milestone instruments that shaped the sound of music:

  • Moog Modular (1960s): One of the first commercial synthesizers, used by artists like Wendy Carlos and Keith Emerson
  • Minimoog (1970): The first portable, affordable synthesizer that brought synthesis to the masses
  • Yamaha DX7 (1983): Popularized FM synthesis and defined the sound of 1980s pop music
  • Roland TB-303 (1982): Originally a bass accompaniment device that later became central to acid house music
  • Nord Lead (1995): One of the first “virtual analog” synthesizers, combining digital technology with the workflow of analog synths

Creating Your Own Sounds

Now that you understand the basics of synthesis, here are some starting points for creating common sounds:

Bass Sound

  • Use a sawtooth or square wave
  • Set a short attack, medium decay, medium-high sustain, and short release
  • Apply a low-pass filter with a moderate cutoff
  • Focus on the lower octaves of your keyboard

Pad Sound

  • Use multiple detuned oscillators
  • Set a long attack, long decay, medium sustain, and long release
  • Apply a low-pass filter with a moderate cutoff
  • Add chorus effect if available
  • Consider adding subtle LFO modulation to create movement

Lead Sound

  • Use sawtooth or pulse waves
  • Set a short attack, medium decay, high sustain, and medium release
  • Apply a resonant filter with modulation
  • Consider adding vibrato with an LFO

Percussion Sound

  • Use noise or short-decay oscillators
  • Set a very short attack, short decay, zero sustain, and short release
  • Experiment with band-pass or high-pass filters

Conclusion

Synthesizers might seem complex at first, but they’re built on relatively simple principles: generating sound waves, shaping them over time, and filtering their frequency content. The true power comes from combining these elements in creative ways.

Whether you’re a musician looking to create your own sounds, a producer aiming to understand your tools better, or simply curious about how electronic music works, understanding synthesis opens up a world of sonic possibilities.

Remember that there are no strict rules in sound design — experimentation often leads to the most interesting results. Happy synthesizing!

Further Resources

If you want to dive deeper into the world of synthesis, here are some excellent resources:

  • Books:

    • “Welsh’s Synthesizer Cookbook” by Fred Welsh
    • “Sound Synthesis and Sampling” by Martin Russ
    • “Becoming a Synthesizer Wizard” by Simon Cann

  • Online Learning:

  • Free Software Synthesizers:

    • Vital - Spectral warping wavetable synthesizer
    • Surge - Open-source hybrid synthesizer
    • Dexed - FM synthesizer based on the DX7