Subtractive Synthesis

Subtractive synthesis is one of the oldest types of synthesis introduced with the birth of analog (modular) synthesizers in the 1960s and 1970s. That's why this type of synthesis is often called "analog." For instance, most analog synthesizers use this method to generate sound.  

Analog Synthesis

The following is an example of subtractive synthesis and components' signal path, which might occur in an electronic instrument. Specifically,  3 main components comprise it:

1. Oscillator
2. Filter
3. Amplifier

• The oscillator creates a sound that a filter can process in several ways. Consequently, it's sent to an amplifier where the volume of the sound can be controlled. Two main oscillator parameters, waveform and frequency (pitch), are available for alteration and control. Waveform is the specific structure of the soundwave that the oscillator is emitting. Usually, there are 4 main types (Sine, Saw, Square, and Triangle.) The sine waveform is the simplest sound, which consists of a fundamental tone. In addition, it has no harmonics, meaning there is not much to filter out when the sound reaches the filter component. On the other hand, there is a saw waveform that is rich in harmonics and has a very buzzy sound. The pitch parameter is another word for frequency or waveform speed. While the frequency is often referred to in Hertz, the pitch is represented in notes and octaves on the keyboard.
• Filter works by removing the parts of the frequency spectrum. It first defines the cutoff point represented in Hz and, depending on the chosen filter type (Low Pass, Hi-Pass, Band Pass…) removes frequencies above, below, or around the cutoff point. Besides cutoff, resonance or emphasis is also involved in the filter. Resonance works by boosting the frequencies near the cutoff point in order to emphasize what the filter is doing.
• The amplifier controls the sound's volume, leading to envelope modulation.

LFO & Envelope Generator

Indeed, there are numerous ways in which we can modulate the parameters of these components. The most common way would be to use the envelope generator and low-frequency oscillator (LFO) for amplifier and filter components. The envelope generator is basically multiplying values with a range from 0 to 1. Usually, 4 points, Attack, Decay, Sustain, and Release, change over time. An envelope generator can also control the volume. However, it is also applicable to any other synthesizer parameters. LFO (Low-frequency oscillator) is similar to the oscillator, but instead of transmitting sounds, it transmits values like the envelope generator. The LFO also usually works at a much lower frequency than the oscillator. Just like with the normal oscillator with the LFO, we can control the waveform and the frequency.  

Additional Resource & Source Texts

• Synth Stabs
• West Coast Grooves
• Ways to Wobble
• Methodical Synthesis
• Steps to Talking Synths
• Synthesis