Synthesis 101 | An Introduction to Subtractive Synthesis

TABLE OF CONTENTS

• Subtractive Synthesis
• Voltage Controlled Oscillators (VCO)
  • Sine Wave
  • Square Wave
  • Triangle Wave
  • Sawtooth Wave
  • Why Feet Instead Of Octave?
• Voltage Controlled Filters (VCF)
  • Moog 24dB Per Octave Four Pole Ladder Filter
  • State Variable Filter
• Envelope Generator (EG)
  • Attack, Decay, Sustain & Release (ADSR)
  • Delay & Hold
• Low-Frequency Oscillator (LFO)
• Voltage Controlled Amplifier (VCA)
• Noise Generator
• Mixers
• Preamp
• Signal Flow
• Polyphony
  • Monophonic
  • Duophonic
  • Polyphonic
  • Paraphonic
• Semi-Modular vs Desktop Synthesizers
  • Semi-Modular Synthesizers
  • Desktop Synthesizers
• What are the benefits of using an Analogue Synthesizer?
• Where to go from here?

Subtractive Synthesis

Subtractive synthesis is a sound synthesis technique that involves starting with a rich, complex waveform and then removing (or subtracting) certain frequencies to shape the desired sound. This is typically achieved using filters, which can alter the harmonic content of the sound by cutting out specific frequency bands. The primary types of filters used in subtractive synthesis include low-pass, high-pass, band-pass, and notch filters. In a typical subtractive synthesis setup, an oscillator generates a waveform, such as a sawtooth or square wave. This waveform is then passed through a filter, which can be modulated by an envelope generator or LFO (low-frequency oscillator) to create dynamic changes in the sound over time. By adjusting parameters such as cut- off frequency and resonance, sound designers can achieve a wide variety of timbres and textures. This method of synthesis is favored in electronic music production due to its versatility and the ease with which it can create evolving sounds. It is widely used in synthesizers, both hardware and software, to produce everything from bass lines to leads and pads.

Voltage Controlled Oscillators (VCO)

Voltage Controlled Oscillators (VCOs) are a key component in analogue synthesizers, generating the audio signals that form the basis of electronic music. VCOs are controlled by voltage inputs, allowing for precise tuning and modulation of the oscillator's frequency. This voltage control enables dynamic and expressive sound manipulation. VCOs produce different waveforms, such as sine, triangle, sawtooth, and square waves. Each waveform has its own unique timbre and character, offering a wide range of sonic possibilities. VCOs can be modulated by other voltage sources, such as LFOs (Low-Frequency Oscillators) or envelopes, to create evolving and complex sounds. Frequency modulation adds movement and depth to the audio signal. VCOs need to be accurately tuned and calibrated to ensure they track correctly across the keyboard. Proper tuning ensures that the oscillator produces the correct pitch at every key press. VCOs can also be synchronized with other oscillators or modulated using frequency modulation (FM) to create rich and evolving textures. These techniques are commonly used in sound design and electronic music production.

Sine Wave

The sine wave is the purest waveform, characterized by its smooth and continuous oscillation. It produces a clean tone without any harmonics, making it ideal for creating sounds that are soft and mellow, such as bass notes or simple melodic lines. Sine waves are often used in synthesizers for generating pure tones, and they are commonly found in applications like audio testing and creating bell-like sounds. Their lack of overtones makes them perfect for subtractive synthesis, where additional harmonics are added later.

Square Wave

The square wave has a distinct, rich sound due to its prominent harmonics, which are odd-numbered multiples of the fundamental frequency. This waveform is often associated with a more aggressive and punchy tone. Square waves are excellent for creating leads, basslines, and percussive sounds. They can evoke a sense of nostalgia, reminiscent of classic video game soundtracks, and are frequently used in pulse-width modulation techniques to create dynamic sounds.

Triangle Wave

The triangle wave sits between the sine and square waves, offering a softer sound than the square wave but with more harmonic content than the sine wave. Its tonal quality is often described as warm and rounded, making it suitable for pads, soft leads, and gentle bass sounds. Triangle waves are commonly used in subtractive synthesis and can be effective for creating sounds that require a smooth attack and decay, such as strings or flutes.

Sawtooth Wave

The sawtooth wave is characterized by its sharp, aggressive sound, containing both even and odd harmonics. This rich harmonic content makes it one of the most versatile waveforms in synthesis. Sawtooth waves are commonly used for creating bright leads, lush pads, and powerful bass sounds.

Why Feet Instead Of Octave?

When exploring the world of synthesizers, you may have encountered the term "feet" in relation to synth oscillators, particularly in the context of organ-style instruments. This terminology can be a bit confusing, especially when compared to the more commonly known "octaves." In synthesizers, the use of feet allows for a more nuanced understanding of pitch relationships. Each foot measurement corresponds to a specific frequency, with 8 feet being the standard pitch. When you double the length (or halve the feet measurement), you drop an octave. This system provides a straightforward way to conceptualize how different oscillators will interact musically. When programming a synthesizer, understanding the feet measurement can help you achieve the desired harmonic relationships. For example, setting an oscillator to 4 feet will produce a sound that is two octaves higher than one set to 16 feet.

Voltage Controlled Filters (VCF)

VCFs are electronic circuits that selectively allow certain frequencies to pass through while attenuating others. This is achieved by adjusting the cutoff frequency, resonance, and other parameters using voltage control inputs. There are various types of VCFs, including low-pass, high-pass, band-pass, and notch filters. Each type has its own unique characteristics and applications in sound design. The resonance control on a synthesizer allows you to boost frequencies near the cutoff point. This creates a peak in the frequency response curve, emphasizing certain frequencies and giving the sound a more pronounced and resonant quality. At high resonance settings, some filters can exhibit self-oscillation, where the filter starts to produce its own sound without an input signal. This can create unique and interesting tones for your music. VCFs are voltage-controlled, meaning that the filter parameters can be modulated in real-time using control voltage signals from sources such as envelope generators, LFOs, and sequencers. VCFs are commonly used to sculpt the timbre of audio signals, creating dynamic and evolving sounds. By modulating the filter parameters, users can achieve a wide range of tonal variations and textures.

Moog 24dB Per Octave Four Pole Ladder Filter

A ladder filter is a type of electronic filter that is commonly used in synthesizers to shape sound by allowing certain frequencies to pass while attenuating others. The term "ladder" comes from the filter's circuit design, which resembles a ladder with rungs. This design typically consists of multiple stages of capacitors and resistors, creating a smooth and musical response to different frequencies. Ladder filters are particularly known for their warm and rich tonal characteristics, making them a favorite among musicians and sound designers.

The filter's cutoff frequency is where the signal begins to be attenuated, usually measured in dB per octave. For example, a 24 dB/octave ladder filter will reduce the signal level by 24 dB for every octave above the cutoff frequency. Poles refer to the points in the filter's frequency response where the gain drops off. Specifically, each pole represents a -6 dB reduction in gain for every octave above the cutoff frequency. The Moog ladder filter typically features four poles, which means that it provides a -24 dB/octave roll-off. This steep cutoff allows for a more pronounced filtering effect, making it ideal for creating dramatic sound changes. 

State Variable Filter

A state variable filter (SVF) is a type of active electronic filter that can produce low-pass, high-pass, band-pass, and notch filter responses from a single circuit configuration. The state variable filter operates by using feedback and multiple stages of filtering to achieve its desired response. The filter's design allows it to maintain stability while providing a smooth transition between different filter types. 

Envelope Generator (EG)

This tool is used to shape the amplitude of a sound signal over time, allowing for dynamic and expressive control over the sound. An envelope generator creates a series of control signals that determine how a sound evolves over time. 

Attack, Decay, Sustain & Release (ADSR)

It typically consists of four main stages: attack, decay, sustain, and release (ADSR). The attack phase controls how quickly the sound reaches its peak volume, the decay phase sets how quickly the sound decreases after the attack, the sustain phase determines the level at which the sound is held once the decay phase ends, and the release phase controls how quickly the sound fades out after the sustain phase. Envelope generators are commonly used in synthesizers to shape the sound of individual notes or sounds. They can be used to create a variety of effects, from sharp plucks and percussive sounds too long, evolving pads and drones. Envelope generators can be applied to various parameters beyond just volume, such as filter cutoff frequency, pitch, and modulation depth. This versatility allows for a wide range of creative possibilities in sound design.

Delay & Hold

The delay function introduces a pause before the envelope begins its attack phase. This is particularly useful for creating sounds that require a gradual onset, such as a swelling pad or a soft lead. By adjusting the delay time, you can determine how long the sound waits before it starts to rise in intensity.

Once the attack and decay phases are complete, the hold function allows you to sustain the envelope at a specific level before it transitions to the release phase. This is beneficial for maintaining a consistent sound level for a desired duration, giving you the flexibility to create more complex textures. For instance, in a percussive sound, you might want to hold the peak level for a moment before it fades away, adding depth to your sound.

Low-Frequency Oscillator (LFO)

An LFO is a type of oscillator that operates at a frequency below the audible range, typically between 0.1 Hz and 20 Hz. It generates a repeating waveform that can be used to modulate parameters such as pitch, volume, and filter cutoff. LFOs are often used to add movement and dynamics to sounds by modulating different aspects of the sound. For example, applying an LFO to the filter cutoff of a synthesizer can create a wobbling effect known as a filter sweep. LFOs can produce various waveforms, including sine, triangle, square, and sawtooth waves. Each waveform has a unique sound and can be used to achieve different modulation effects. Experimenting with different waveforms and modulation techniques can help you unlock the full potential of subtractive synthesis in your music.

Voltage Controlled Amplifier (VCA)

The VCA is responsible for amplifying or attenuating the incoming sound signal based on the control voltage it receives. When the control voltage is high, the VCA amplifies the signal, making it louder. Conversely, when the control voltage is low, the VCA attenuates the signal, making it quieter. One common application of VCA synthesis is using an envelope generator to shape the volume of a sound signal over time. By controlling the attack, decay, sustain, and release parameters of the envelope, you can create dynamic and expressive sounds with varying levels of volume. In VCA synthesis, the amplitude of a sound signal is controlled by an external voltage source. This voltage source can come from various sources such as an envelope generator, LFO (Low-Frequency Oscillator), or even a MIDI controller. By modulating the voltage, you can dynamically adjust the volume of the sound signal.

Noise Generator

White noise is a type of noise that contains all frequencies at equal intensity, making it sound like static or the sound of wind. When used in subtractive synthesis, white noise can be used to add texture and brightness to a sound. It is often used to create percussive elements, such as hi-hats or snare drums.

Pink noise, on the other hand, is a type of noise that has equal energy in each octave, making it sound more balanced and natural than white noise. When used in subtractive synthesis, pink noise can be used to add warmth and depth to a sound. It is often used to create basslines or pad sounds.

Mixers

Introducing multiple sound sources will require flexible control over the individual level controls. The mixer has individual level controls for each input source, allowing you to adjust the volume of each signal. By changing the levels of the input sources, you can create dynamic and evolving sounds. Some mixers will have the potential to blend the amount of modulation. Alternating the control of these levels can dramatically evolve the timbre of the patch.

Preamp

The last stage of the signal chain is the preamp. It prepares the signal for the next stage in the audio chain, ensuring that the sound has enough volume and clarity before being sent to other equipment. While both a VCA and a preamp are used to manipulate audio signals, their primary functions differ: a VCA is used for control and automation of volume levels, whereas a preamp is used for boosting the signal strength of audio sources.

Signal Flow

An important aspect of synthesis sound design is the understanding of the synths particular signal. Signal flow refers to the pathway through which signals are generated, processed, and transmitted in a synthesis system. This flow typically involves various stages, including the creation of sound waves, modulation, and filtering, leading to the final output of the synthesized audio. Understanding the synthesis signal flow is crucial for sound designers and musicians to effectively manipulate and craft their desired sonic outcomes. Every synth has their own predetermined signal flow, determined by how they are produced. Some synths will have the option to “break”, or “alter” its predetermined flow. These are known as semi-modular, or modular synthesizers.

Polyphony

Polyphony refers to the combination of two or more distinct melodic lines that are harmonically interdependent yet rhythmically independent. Your synthesizer may have constraints on the number of notes it can generate at the same time. Comprehending your synth's limitations is essential for determining the tonal possibilities available.

Monophonic

Monophonic synthesis refers to the ability of a synthesizer to produce only one note at a time. This means that if you play multiple keys simultaneously, only the first note will sound. Monophonic synthesizers are often favored for lead sounds, bass lines, and solos.

Duophonic

Duophonic synthesis allows for two notes to be played simultaneously. In duophonic mode, one note can be played on one oscillator while another note is played on a second oscillator.

Polyphonic

Polyphonic synthesis is the most versatile of the four types, enabling the playback of multiple notes at once—typically ranging from four to several dozen voices, depending on the synthesizer. These added voices makes them ideal for lush pads and intricate harmonies.

Paraphonic

Paraphonic synthesis is a hybrid approach that allows for multiple notes to be played, but with a shared filter. This means that while you can play chords, they will all be processed through the same filter, resulting in a unified sound. Paraphonic synthesizers can create interesting textures and are often used for unique sound design.

Semi-Modular vs Desktop Synthesizers

Semi-Modular Synthesizers

Semi-modular synths are standalone synthesizers that come with a pre-wired signal path, making them easier to use for beginners. They often have built-in modules for oscillators, filters, and envelopes, but also offer the flexibility to patch in additional modules for more customization. Semi modular synths are a great option for musicians looking for a balance between ease of use and flexibility in sound design.

Desktop Synthesizers

Desktop synths are compact synthesizers that are designed for portability and ease of use. They often feature a simplified interface with fewer controls compared to modular synths, making them more accessible for beginners. Desktop synths are a great option for musicians who want a versatile synthesizer that is easy to transport and use in a variety of settings.

What are the benefits of using an Analogue Synthesizer?

Analogue synthesizers are known for their warm, rich sound. This warmth comes from the continuous voltage signals that analogue circuits produce, creating a natural harmonic distortion that many musicians find appealing. The imperfections inherent in analogue circuitry contribute to a unique character in the sound, making it feel more organic and alive.

Where to go from here?

As you have probably learnt by now, the world of synthesis can get incredibly complex. We have only just scratched the surface on synthesis. There are many avenues to explore. Often, the more you put into your sound design, the better of a result you will get out of it. There is a multitude of great Moog products out there that can suit a variety of sound and skill levels. If you have any questions then please feel free to contact Moog’s dedicated support team, who will be happy to assist you.