[korg]
[ms50 title]

[owners manual]

2. How the synthesizer works  ^

 Kinds of signals
 Types of modules
 Connecting modules


A synthesizer uses a number of different modules (VCO, VCF, VCA, EG, MG, and so on) hooked together to make any one sound. Each of these modules affects the sound in a particular way.

When you want to synthesize a sound, you first have to choose the right modules. Then you have to decide how to connect or "patch" them together.

What you are really doing is using the signals from some modules to control the signals of others. A basic knowledge of these signals is essential for sound synthesis.


[figure]
- the basic organisation of a synthesizer

[bullet] KINDS OF SIGNALS ^

Three kinds of signals flow between the modules. As shown in the figure above, these are:
(1) [solid arrow 1] sound signals,
(2) [solid arrow 2] control voltage signals, and
(3) [broken arrow] trigger signals.

(1) Sound signal (audio signal)

An AC signal of 20Hz ~ 15kHz, covering the frequency range audible to the human ear. The VCO generates this signal, after which the VCF and VCA affects its timbre and volume, respectively.

(2) Control voltage signals (CV)

These control the VCO (which determines pitch), the VCF (timbre), and the VCA (volume). There are several different kinds of control signal (CV).

[bullet] Keyboard CV (KBD CV)
On most synthesizers, the keyboard generates the signals that determine the VCO's pitch. Basically speaking, the higher the note you play, the higher the voltage. But depending on the synthesizer manufacturer, there are two different systems for converting voltage to pitch (frequency). Korg and Yamaha use the Hz/V system, all others use the Oct/V system. You can use either kind of keyboard with the MS-50, since its VCO has both kinds of KBD CV input jacks.

[bullet] Envelope signal (ENV)
In the preceding section you saw graphs of the difference between regular repetitive changes (vibrato, tremolo), and those that occur individually. Envelope signals control individual changes. The EG (envelope generator) produces the envelope signals which control the VCA's effect on a sound's volume changes over time.

When you play a note on the keyboard, it triggers the beginning of EG operation. You use the EG's "attack", "decay", "sustain", and "release" knobs to shape each section of the envelope signal shown in the figure below:

[figure]
- ADSR type envelope signal

For pitch bends, delayed vibrato, and other effects, you use a "DAR" (delay, attack, release) type of envelope generator to program the kind of envelope signal shown in the figure below:

[figure]
- DAR type envelope signal

[bullet] Repetitive signal (MG)
The MG (modulation generator) produces this kind of signal used for vibrato, tremolo, and other cyclic effects. You can choose from a variety of output waveforms. For example, a triangle wave gives ordinary vibrato, but you can use a rectangle wave to synthesize the sound of a police siren.

(3) Trigger signal (TRIG = [ground])

This tells the EG (envelope generator) when to start and stop. Trigger signals can be produced by a keyboard, trigger switch, foot switch, or MG (modulation generator).

As with the KBD CV, there are two kinds of trigger signals; Korg, Yamaha, Moog, etc., use "[ground]", but some manufacturers use "[ground up]". On the MS-50 you can use the inverter and adding amp to change one kind into the other. However, the Korg MS-02 Interface is recommended for this sort of "translator' role.


[bullet] TYPES OF MODULES ^

A synthesizer's modules (KEYBOARD, VCO, VCF, VCA, EG, S/H, MG, etc.) fall into three basic categories which we will examine within the context of "you are what you eat" model of sound synthesis.

1) Raw materials: EG-1, EG-2, MG, voltage supply (VS), noise generator (NG), And external signal inputs are like the different sections of a supermarket which supply you with poultry, vegetables, flour, and other groceries. Of course, these can sometimes be eaten without any further preparation.

2) Kitchen appliances: S/H, modulation VCA, adding amp (ADD AMP), integrator (INT), inverter (INV), ring modulator (RM), divider (DIV), etc., are the appliances and utensils you use to prepare to prepare and cook your raw materials. The way you cook the food, as well as the raw materials you use, will control the behavior of those who eat it.

3) Mouths to feed: The VCO, VCF, and VCA will act differently depending on what you feed them. It is these three modules that directly handle the audio (sound) signal and give it pitch, timbre and volume characteristics. Therefore, you have to know exactly what kind of signal each module generates, and which elements of the final sound it will modulate (via the VCO, VCF, or VCA).


[bullet] CONNECTING MODULES ^

To synthesize any particular sound, you need to proceed in three steps:
(1) Analyse the sound you have in mind; break it down into its three elements and look at each individually. (ANALYSIS)
(2) Select the modules you will need according to the results of your analysis. (SELECTION)
(3) Program your selected modules by connecting them together and adjusting their control knobs. (PROGRAMMING)

Analysing a sound means figuring out why it sounds the way it does. Ask yourself: What is its pitch? What kind of timbre does it have? How does its volume change over time? Then visualize each of these elements in the form of separate graphs (as described earlier in "What you need to know to synthesize sounds").

When you select modules, decide which ones will be able to help produce the pitch, timbre, and volume changes that you analysed. To choose the right modules, you must have a clear idea of exactly what each module can and cannot do.

Programming the modules is a matter of hooking them up in the right order and setting the knobs for the effects you need.


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