COLUMNS
Semi-Modular Synth Basics
An Excerpt from Patch & Tweak with Korg
This is an exclusive excerpt shared with Canadian Musician from the book Patch & Tweak with Korg by Kim Bjørn . Published by BJOOKS , the new 216-page book journeys through semi-modular synthesis through the lens of Korg and ARP synthesizers . For more information , go to
www . bjooks . com .
A semi-modular synthesizer is the perfect place to start learning synthesis , because you can get sound out of it without using any external patch cables . While we ’ ll look at the differences between the ARP 2600 M , MS-20 mini , and volca modular later on , they share some common functional ‘ blocks ,’ which provide the basis of creating sound with them . Though a lot of parameters are usually made available for you to see and access on their patch panels , we ’ ll first look at the basics , and then we ’ ll explore the possibilities of patching in much more detail throughout the rest of this book .
Sound sources The most common sound sources in a synth will be one or more oscillators – electric circuits that create audible tones . Other possible sound sources include a noise generator , a sound from another device patched into the external input , or a very fast oscillating voltage source like an LFO or a looping envelope . The sound sources are often ( but not always ) mixed together before further processing to refine the timbre .
Timbral processing To go beyond the raw timbre of the sound sources , harmonics and frequency content can be added or removed with various tools .
Filtering Filters remove unwanted frequencies from the raw material so that you can shape notes and the overall sound to your liking . The lowpass filter , which removes higher frequencies , is the most common type . The MS-20 also offers a high-pass filter , which removes the lower frequencies and lets the higher ones pass .
Waveshaping / wavefolding Waveshaping occurs when we directly alter the original shape of the waveform . On the volca modular , the wavefolder does this by literally folding the waveform back onto itself . On the MS-20 mini , you can ‘ skew ’ its modulation waveforms .
Shaping of volume Usually , envelopes are used to control the amplitude of a sound over time from note-on to noteoff . Envelope generators are used for this purpose , but modulation sources as LFOs can also be used or sounds weaving in and out . Commonly , gates are used to control envelope generation ; the gate signal tells the synthesizer how long a key or note is held before it ’ s released . Events can be triggered and / or held when a gate is opened – and also when it is closed again .
VCAs and processing Voltage Controlled Amplifiers process a signal by using another signal to control it . Usually it is an audio signal being controlled by an envelope or modulation source . However , it can also be a control voltage ( such as an LFO ) being altered by another LFO . VCAs are your most common tools to alter audio and control voltages .
Mix and output + effects Finally , the resulting sound is output . At this stage , further sound sources could be mixed in , bypassing the filtering and volume modulation , etc . This is where effects of various kinds , like reverb or delay , are added . The volca modular and ARP 2600 M both have a reverb effect ; other effects can be created in various ways , or external effects processors can be used on the output signal .
Modulation Modulation creates movement in sounds . There is always a modulation source ( for example a waveform , or an envelope ) and a modulation destination ( for example the filter frequency ). Modulation waveforms are often generated at low frequencies ; the common term for this is LFO ( Low Frequency Oscillator ), but some synths use different names . However , you can also generate modulation at higher frequencies – audio rate modulation – which can be a lot of fun . There are many ways to modulate sound sources to change their timbre – for example , Frequency Modulation , Ring Modulation , and Pulse Width Modulation .
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