Synthesis 101 | Part 1 | An Introduction to Subtractive Synthesis

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.

Pitch, Velocity & Gate

When it comes to synthesizers, understanding the differences between pitch velocity and gate is crucial for creating dynamic and expressive sounds. Here's a breakdown of each concept:

Pitch: Pitch refers to the frequency of a sound wave, which determines the note that is produced. In synthesis, pitch is typically controlled by a keyboard or sequencer, allowing the musician to play different notes and melodies. Adjusting the pitch of a sound can create a wide range of musical effects, from deep bass tones to high-pitched leads.

Velocity: Velocity refers to the speed and force with which a key is pressed on a keyboard, or a pad is struck on a drum machine. In synthesis, velocity can be used to modulate parameters such as volume, filter cut-off, or envelope intensity. By varying the velocity of your playing, you can add dynamics and expression to your sound, making it more realistic and engaging.

Gate: Gate is a control signal that determines the duration of a note or sound. When a gate signal is triggered, it opens the "gate" to allow the sound to be heard, and when the signal ends, the gate closes, stopping the sound. In synthesis, the gate signal is often used to trigger envelopes, such as the amplitude envelope, which controls the volume of a sound over time.

Oscillators

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.

Filters

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.

Envelopes

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. 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.

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.

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.

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.

Noise

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.

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.

Semi-Modular vs Desktop 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 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.

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.