Subtractive Synthesis

Logic subtractive analog synths.

Click or tap the model number  for a page detail

  • ES M  – A simple monophonic synth derived from the Mini Moog suitable for basses and leads.
  • ES P– a simple polyphonic synth suitable for basses.  Individual wave faders and two subs plus built in chorus enable it to sound orchestral in sizes. Key scaling appears here for filter offset etc.
  • ES E – a powerful  two oscillator with sophisticated controller routinge
  • ES 1-  A full blown analog  subtractive synths
  • ES 2 – An advanced polyphonic synth with very sophisticated controller routing
  • EXS 24 – a very powerful sample player with an amazing control mat roux and wave editor

Subtractive synthesis – includes all analog synths and sample players.
The main concept is that you start with a bright sound with lots of harmonics and chip away until you arrive at the sound you are looking for.

There are three basic aspects (known informally as POT, TOT and VOT) each with its own set of tools.

 Pitch Over Time – how pitch changes in a note.
Timbre Over Time – how harmonic content changes in a note.
Volume over time – how loudness changes in a note.

Controllers
Each of these has a set of controllers to shape the sound to your liking.
The main controllers are:
Keyboard – note numbers from 0-127 (Guitar controllers exist also).
Velocity – measures the speed of the key depress 0-127.
Aftertouch – pressing harder on a depressed key generates a controller from 0 to 127.
Envelope Generator ( EG ) has 4 stages AttackDecay, Sustain and Release (ADSR).
Low Frequency Oscillator ( LFO ) creates a low speed control for creating cyclical changes in the sound (vibrato, tremolo, wah etc.)
Mod Wheel – a wheel which could send #CC 1
Pitch Bend – a spring loaded wheel with a center detente.
Sustain Pedal – sending this controller will increase the release time in the same way that pressing the piano loud pedal causes is the sound to die away more slowly.
Other controllers
MIDI actually defines 127 controllers some of which are fixed in function and some of which are assignable.
For example:
CC #1 is modulation.
CC #2 is breath control.
CC #7 is volume.
CC #11 is expression
CC #64 is sustain pedal

For a complete list of MIDI controllers please click here

1. Pitch over time
Pitch is usually generated in the Oscillator section and can have several inputs.

Here is the oscillator part of a Mini Moog. (Click to enlarge)

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1.1 Octave
Curiously we are still using the ranks of pipe organs. I am guessing this is sentimental. Most oscillators support 4″, 8″ and 16″ settings though you can just think of them as octave setting.

1.2 Wave forms
Most synthesizers support sawtooth square and triangle waveforms. The reason for these waveforms is that Bob Moog and his friends used only electrical parts they could find at RadioShack. If you open and close a switch 440 times the second you will generate a square wave at A3. If you flood a capacitor with electricity 440 times a second you will generate a sawtooth wave. In some aspect of physics that I do not yet understand these two harmonic series corresponds to the two harmonic series found in nature. The oscillation of a string fixed both ends ( guitar ) generates sawtooth, the oscillation of a system open at one end (flute) will create a square wave with an Odd Harmonic series

1.3  Keyboard
We use the term keyboard somewhat  loosely  since all it really is just a list of MIDI note numbers numbers from from 0 to 127.  Middle C was defined as note number 60. Where the note numbers come from is irrrelevant. It could be a guitar, it could be a voice, it could be anything. Midi controllers even exist for the gloved hand. Of course the keyboard can be used to control pitch but since it is merely a number between zero and 127 it has many other functions as well.

1.4 Low Frequency Oscillator LFO
A Low frequency Oscillator can be routed to pitch to control typical modulations like vibrato. Usually the values are programmed in the patch but executed with the modulation wheel. Programed LFO values can also be executed using Aftertouch, pressing harder on a key which is already depressed.

The actual pitch produced by the synthesizer is determined by the note number and also settings in the pitch bend, modulation and pitch envelope generator.

1.5 Pitch Envelope Generator
The pitch on musical notes on not necessarily in chewing throughout. For example a guitar string will move so slightly shop sharp at the attack, slightly flat at the decay and stabilize in the sustain section. To generate these we need envelope generator.

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Envelope Generators crop up in all three basic sections (POT, TOT and VOT). They are not common in Pitch so please read the Volume Over Time for a detailed explanation. Simply put they have 4 segments

Attack – time to reach max value.
Decay – Time to move to Sustain segment if the sound sustains
Sustain – level set that will hold as long as a key is held down
Release – a timer that set the tie after note release to reach 0.

3. Volume Over Time
Envelope Generator (ADSR)
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Just like stories, notes have a beginning a middle and an end. The first stage of an Envelope Generator (EG) is called the Attack stage and it defines the amount of time taken for the sound to rise from silence to it’s max initial volume. Once it has reached it’s maximum value control of the sound is passed to the Decay segment. If you want to simulate an instrument where the note dies away ( like a guitar) only the  Attack and Decay sections are needed. On the guitar the note drops to silence over time. However an instrument like the violin will sustain after the initial Decay because it is able to give energy to the string by bowing.  Attack and Decay are both timers. High values will give slow Attacks and Decays, small numbers will give very fast transitions through the first two stages of an envelope generator. The Sustain section is not a timer, it is a level and it will remain at that volume as long as the key is depressed. Once the key is released it will pass control to the release segment of the envelope which again is a timer and controlls how long it takes for the sound to decay to nothing. The release segment simulates how long it takes for the sound to die out of the instrument after the key is released.

Oscillators.
Although the Mini had three oscillators it was only monophonic. The sawtooth, triangle and square waveforms were static.  By adding a second and detuning at slightly the sound would beat. The third could be used as an LFO or as a sub for beef.

2. Time but over time

 

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