How Subtractive Synthesis Works

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Subtractive synthesis is a key method in generating electronic sound. It works by reducing specific frequencies from a sound that has a lot of harmonic content.

Using filters, modulators, and envelope shapers, you can carefully create different sounds by “subtracting” different aspects of the audio. This can be anything from full, sweeping sounds to sharp lead lines.

In this beginner’s guide, we’ll discuss the ins and outs of how subtractive synthesis works, along with some practical applications and tips.

The Fundamentals of Subtractive Synthesis

Subtractive synthesis all about reducing harmonics from rich waveforms to create unique musical sounds.

This means we are removing certain frequencies to shape the sound that we want to create. By changing a filter cutoff point, music makers can decide which harmonics are reduced. This strongly affects the sound that’s produced.

Music makers start with a simple waveform like a sawtooth or square wave. These waves have a lot of different harmonics.

For example, a low-pass filter can be changed to let lower frequencies through while blocking higher ones. This can make the sound brighter and more resonant.

Another key part of subtractive synthesis is changing the waveform itself through modulation.

The skill in subtractive synthesis is knowing how these elements – filter cutoff, changing the waveform, shaping the frequency, creating the sound, and removing harmonics – work together.

Subtractive Synthesizers

Subtractive synthesis is one of the most fundamental ways to synthesize sounds. It’s been the foundation of all sound generation and design.

Here are some of the most popular subtractive synths in use today:

  1. Moog Sub 37: Moog is a company with a strong heritage in subtractive synthesis. The Sub 37 is an excellent example, offering a wealth of knobs and buttons for hands-on control.
  2. Dave Smith Instruments Prophet 6: This is a true analog, subtractive synth which is highly respected within the industry.
  3. Roland SH-101: This is a classic, vintage subtractive synth that is still widely used today, despite being discontinued.
  4. Arturia MiniBrute 2: This is a modern, analog subtractive synthesizer with a semi-modular architecture that makes it very flexible.
  5. Korg Minilogue: This is a polyphonic analog synthesizer that offers a lot of subtractive synthesis features in a compact and affordable package.
  6. Behringer DeepMind 12: This is a 12-voice analog polyphonic synth with a focus on subtractive synthesis.
  7. Novation Bass Station II: This is a modern, analog subtractive synthesizer with a focus on bass sounds.
Moog Sub 37 Subtractive Synthesizer
The Moog Sub 37 Analog Synthesizer

Core Subtractive Synth Components

One main part of a synthesizer is its ability to control voltage. This lets it change sounds in many ways. It has parts called oscillators that actually generate the basic sound waves. Then, filters shape these waves by taking away or reducing certain sound frequencies.

Other parts called envelopes control how the sound changes over time. These usually have stages called Attack, Decay, Sustain, and Release, which dictate how the sound plays back – does it sustain or is it short and stabby?

Voltage-controlled amplifiers, or VCAs, control how loud the sound is. Low-Frequency Oscillators, or LFOs, add effects like vibrato and tremolo.

These parts together make a system that lets musicians and producers play around with and make unique sounds via subtractive synthesis.

They can make everything from the strong bass and sharp lead sounds in electronic music to the airy sounds in movie scores.

How Subtractive Synth Controls Work

Let’s dive deeper into the various synth components you just learned about and see how they work to generate sounds.

Oscillators and Waveform Basics

Oscillators are the main sound makers in subtractive synthesizers. They make the first sound waves that are later shaped.

These sound waves can be different types like sine, square, sawtooth, and triangle. Each type has its own unique sound and set of harmonics/overtones. Changing the shape of these waveforms helps to create different sounds.

The oscillator’s output starts the process of creating harmonics. A square wave, for example, has odd harmonics that give it a special sound. You can change these harmonics to shape the sound using various techniques

Subtractive synthesis is about making the sound you want by taking away frequencies from the oscillator’s output.

This is done with filters and other tools that shape the sound and give it its final character.

The Role of Filters

Filters are important in subtractive synthesis because they shape sound frequency. They help us to cut out exact parts of a sound to get the tone we want.

There are different types of filters like low-pass, high-pass, band-pass, and notch filters. Each one changes the harmonic content of a waveform in its own unique way. This gives us lots of options for shaping sound.

  • High Pass Filter: This type of filter allows signals with a frequency higher than a certain cutoff frequency to pass through.
  • Low Pass Filter: This filter allows signals with a frequency lower than a certain cutoff frequency to pass through
  • Band Pass Filter: This filter allows signals within a certain frequency range to pass through while attenuating frequencies outside this range.
  • Notch Filter: Also known as a band-stop or band-reject filter, it allows signals at all frequencies to pass through except for those in a specific range, which are attenuated.
Filter Types Shown Visually

Resonance effects are a key part of using filters. They focus on frequencies around the filter’s cutoff point. This can add a unique peak and may even add a singing or whistling quality to the sound.

Resonance can highlight certain harmonics, which makes it a strong tool for expressive sound shaping in subtractive synthesis.

Cutoff modulation is also really important. It lets us control the filter’s frequency limit dynamically.

By changing the cutoff point, either by hand, with an envelope, or with a Low-Frequency Oscillator (LFO), we can create changing textures and movement within a patch.

Envelopes and Sound Shaping

Envelopes are very important for shaping the sound of music. They help make the sound change over time, from when it first starts to when it ends.

This is done by adjusting the attack, decay, sustain, and release stages of a sound. By doing this, sound designers can give a unique sound to a musical instrument or sound effect.

  • Attack: This refers to the initial phase of the sound where it builds from silence to its maximum level. The attack time is the duration it takes for this buildup.
  • Decay: After the attack phase, the sound starts to decrease in volume. This reduction phase until it reaches a steady state is known as the decay.
  • Sustain: This phase is the steady state where the sound maintains a constant level over time. The sustain level is the volume at which the sound will continue until the key is released.
  • Release: This is the final phase where the sound fades out to silence after the key is released. The release time is the duration it takes for the sound to completely fade out.
ADSR Envelope Diagram

Envelopes can do more than just shape the sound. They can also change the sound’s colour or tone. This is done by using envelopes to control things like the filter cutoff or pitch.

This makes the sound change and grow over time. It can change a sound from being short and sharp to being smooth and long-lasting.

Envelopes can also be used with other tools to shape sound, like LFOs or sequencers.

Modulation With LFOs

Low-Frequency Oscillators, or LFOs, help make sound more dynamic in subtractive synthesis by adding layers of modulation. They make static sounds more lively.

They create changes in pitch, filter cutoff, or loudness by oscillating at frequencies you can’t hear. These changes result in effects like vibrato, tremolo, or sweeping.

LFOs do more than just create simple vibrato effects, though. They can make a sound richer and more animated when they change the pulse width of square waves or a filter’s frequency, for example.

By controlling different parameters at the same time or changing another LFO’s rate or intensity, LFOs can create complex rhythms and textures.

By using different waveforms like triangle, sine, or random step, and changing the rate and depth, you can create unique sound modulations. Plus, you can create complex and unpredictable sound modulations by automating LFO parameters.

Crafting Sounds With Subtractive Synths

With subtractive synthesis, you can control a sound to make it more emotional and interesting. Playing around with oscillators and modulation sources can lead to new sounds that make a genre stand out.

In modern music, it’s popular to mix different genres together. Artists take bits from different types of music to make something new and exciting.

Subtractive synthesis is great for this because it’s flexible and expressive. It lets artists blend different sounds together to make songs that don’t fit into just one genre.

The process of subtractive synthesis is like carving a sculpture. You take away frequencies to find the core sound of a genre.

Here are some of the best use-cases for subtractive synthesis:

  1. Bass Sounds: Subtractive synthesis is often used in creating deep and rich bass sounds. These sounds are typically created by using low-pass filters to remove high frequency components, leaving behind lower frequencies.
  2. Pads: Pads are sustained background or harmony sounds. Subtractive synthesis is great for creating these types of sounds as it allows for tonal shaping through filtering and modulation.
  3. Leads: Lead sounds are often created using subtractive synthesis. The ability to manipulate waveforms and filter frequencies makes it possible to create sharp, cutting leads or soft, warm leads.
  4. Percussion: Subtractive synthesis can also be used to create percussive sounds. By quickly modulating the amplitude and/or pitch of a sound, you can create drum-like or percussive effects.
  5. Special Effects: The flexibility of subtractive synthesis makes it great for creating special effects. This could include everything from sci-fi soundscapes to realistic sound reproductions.
  6. Plucked Strings: By modulating the amplitude and pitch, you can mimic the sound of a plucked string instrument.
  7. Brass Sounds: By using resonance and careful filtering, subtractive synthesis can create powerful brass sounds.
  8. Wind Instruments: Subtractive synthesis can also be used to create wind instrument sounds by altering the attack and decay parameters and using careful filtering.
  9. Vocal Sounds: By using formant filters, subtractive synthesis can simulate the human voice or choir sounds.
  10. Synth Pop Sounds: The characteristic sounds of 80s and 90s synth pop music are often created using subtractive synthesis. These sounds can be bright and expressive, or soft and mellow, depending on how the synthesis parameters are set.

Subtractive Synthesis Workflow Example

Creating a Classic Bass Sound using Subtractive Synthesis:

  1. Select a Waveform: The sound designer starts by selecting the initial waveform that will be manipulated to create the desired sound. For a classic bass sound, a sawtooth or square wave is a good starting point due to their harmonic-rich properties.
  2. Set the Oscillators: The sound designer then sets the oscillators, which generate the raw sound. For a thick, rich bass sound, they might detune two oscillators slightly against each other.
  3. Adjust the Filter: The next step is to adjust the filter, which subtracts certain frequencies from the sound. For a classic bass sound, the designer might use a low-pass filter to remove high frequencies and emphasize the low end.
  4. Modify the Envelope: The sound designer then adjusts the envelope, which controls how the sound evolves over time. For a bass sound, they might set a fast attack (so the sound starts immediately when a note is played), a medium decay (so the sound decreases in volume after the initial attack), a sustain level to preference (how loud the sound is while the note is held), and a medium release (so the sound doesn’t cut off abruptly when the note is released).
  5. Add Effects: Finally, the sound designer might add some effects to enhance the sound. For a classic bass, they might add a bit of distortion to give it some grit or a chorus effect to make it sound bigger.
  6. Tweaking: After the initial sound is created, the sound designer would spend time fine-tuning and tweaking the parameters to get the exact sound they want.
  7. Save the Patch: Once satisfied with the sound, the sound designer would save the patch in the synthesizer, so it can be recalled and used in the future.

This is a basic workflow breakdown. The sound design process can be much more complex and involves a lot of experimentation and fine-tuning.

The History and the Future of Subtractive Synthesis

The concept of subtractive synthesis dates back to the early days of electronic sound generation. In the 1960s and 1970s, subtractive synthesis was the basis of most analog synthesizers.

These synthesizers, such as the Moog and ARP, used oscillators to produce simple waveforms, and filters to subtract frequencies from those waveforms.

The name “subtractive” comes from the way the signal is processed. Unlike additive synthesis, where different waveforms are combined to create a new sound, subtractive synthesis begins with a full, rich sound and subtracts elements to create something new.

Some of the earliest synthesizers used subtractive synthesis, including the Hammond organ and the Theremin. However, the method became much more popular with the advent of analog synthesizers in the 1960s and 70s.

In the 1980s, the advent of digital synthesizers brought new synthesis methods into the mainstream. However, subtractive synthesis remained popular due to its simplicity and the unique tones it can produce.

Today, subtractive synthesis is a common method used in both hardware and software synthesizers. It is often combined with other synthesis methods to create complex, rich sounds.

Despite the advent of many new synthesis technologies, the basic principles of subtractive synthesis remain a fundamental part of electronic music production.

The Future

What does the future hold for subtractive synthesis? Who knows, but as technology continues to move forward there are some definite possibilities that lie in store:

  1. Deeper Integration with Digital Technology: As digital technologies continue to evolve, we can expect subtractive synthesis to become more deeply integrated with digital interfaces, leading to more sophisticated sound production.
  2. Improved Accessibility: With the rise of digital audio workstations and software synthesizers, more people will have access to subtractive synthesis.
  3. More Complex Sounds: As subtractive synthesis technology continues to improve, it will likely allow for the creation of more complex and varied sounds.
  4. Hybrid Systems: We might see more hybrid systems combining subtractive synthesis with other types of synthesis for more unique sounds.
  5. AI and Machine Learning: With the rise of AI and machine learning, we may see new types of subtractive synthesis that can create sounds based on learning from vast amounts of data.

What to Do Next

Thanks for reading this complete guide on Subtractive Synthesis for beginners. Next up, deep-dive into another area you’d like to learn about below. We recommend taking a look at additive synthesis in this guide.