Subtractive Synthesis

Subtractive Synthesis Subtractive synthesis is the method used to create sounds in most of the classic synths of the 1970s, such as the MiniMoog, ARP 2600 and Oberheim. As opposed to additive synthesis, subtractive synthesis starts with a complex waveform and removes frequencies. Most synthesizers and samplers use the basic concepts of subtractive synthesis to some extent. Subtractive synthesis is also known as analog synthesis, though most are now virtual analog, in other words, digital.

Subtractive Synthesis Signal Path Oscillator Source Modifier Filter Amplifier Power Modulator Modulator Modulator Dynamic- sound changes over time Static- sound remains the same

Oscillators Oscillator are the basic sound source for subtractive synthesis Sine Wave Dull Triangle Wave Hollow tube Most synthesizers include more source waves than the basic ones listed Modulation - frequency Square (Pulse) Wave Woody Sawtooth Wave Buzzy

Filters Used to remove frequencies from basic wave Primary means of shaping a sound Types Low Pass filter (LPF) High Pass Filter (HPF) Band Pass Filter Band Reject Filter (Notch) Special – Formant, Comb

Filter Terms Cutoff Frequency – point at which filter begins to remove frequencies Poles – Each pole removes frequencies at a rate of 6 db per octave Resonance – Accentuation of frequencies around the cutoff frequency

Low Pass Filter Removes frequencies above the Cutoff Frequency 2-pole (12 db/octave) or 4-pole (24 db/octave) Resonance available Creates fat sounds Modulate – cutoff frequency, resonance amt

High Pass Filter Removes frequencies below the cutoff frequency 2-pole (12 db/octave) Creates thin, nasal sounds Modulation – cutoff frequency

Band Pass and Band Reject Filter Two Cutoff Frequencies Band Pass removes frequencies above and below the cutoff frequencies Band Reject removes frequencies between the cutoff frequencies Modulation – Cutoff Hz 1, Cutoff Hz 2

Modulation LFO – Low Frequency Oscillator Envelope Generator - ADSR Means to change a parameter in a device LFO – Low Frequency Oscillator Envelope Generator - ADSR Keyboard - Pitch Keyboard - Velocity Oscillators Controllers In advanced synthesizers virtually any device can modulate another

LFO Continuous device- always on Uses various waveforms or shapes Triangle or Sine wave Ramp up or down Random Modulates device parameters in time Can be synced to tempo/meter

Envelope Generator (ADSR) Attack time Decay time Sustain level Release time One-shot Envelope generators use a trigger and gate. The trigger is usually a depressed key. The gate remains open and the EG remains at Sustain level until the key is released. The envelope then moves to zero based on Release time. Any parameter can be modulated

Subtractive Synthesis Signal Path Oscillator Filter Amplifier Keyboard LFO ADSR