[korg]
[ms50 title]

[owners manual]

1. What you need to know to synthesize sounds  ^

Introduction
1-A Pitch
1-B Changes in pitch
2-A Timbre (tone color)
2-B Changes in timbre
3-A Volume (amplitude)
3-B Changes in volume


Introduction ^

We hear sounds when vibrations in the air reach our ear drums and are transmitted to the brain.

We can break down any sound into the three elements of pitch, timbre (tone color), and volume. Then we can see how each of these changes over time.

A synthesizer works the other way around. It uses a number of modules (VCO, VCF, VCA, EG, MG, and others) to control each of these elements and the way they change. To use a synthesizer you need to understand these elements of sound so that you can decide how to manipulate them.


1-A Pitch ^

"Frequency" or "cycles per second" determine the pitch of a sound wave. Frequency is measured in "Hz" (hertz) units; one Hz equals one cycle per second.

[figure]
- a 15Hz sawtooth wave

The figure above shows how a 15 Hz sawtooth wave goes through fifteen complete cycles every second.

In music, people don't usually use such terms. Instead, we just say "A" for the pitch that has a frequency of 440 Hz. Even more common is the "do, re, mi, fa, so" system for expressing the relative pitch of different notes in a scale.


1-B Changes in pitch ^

Here we are talking about vibrato and pitch. It helps to use graphs to understand these effects. The important questions are: "How many times do you want the pitch to go up and down each time you play a note?" or, "How many times per second do you want the pitch to rise and fall (fluctuation speed)?"

[figure]
- vibrato and pitch bend effects

The figure above shows that in vibrato the pitch fluctuates regularly above and below the basic frequency of a note, but in a pitch bend effect the pitch just changes (rises or falls) once. Be clear about this difference, because you have to use different modules to synthesize these two kinds of effects.


2-A  Timbre (tone color) ^

When we say a sound is bright, dull, clear, or heavy, we are describing its timbre. Timbre depends on the shape of a sound wave, its waveform. Any regular waveform can be broken down into its fundamental frequency and a finite number of harmonic components which are odd and even multiples (overtones) of the fundamental. For example, a 100 Hz sawtooth wave is made up of a mixture of sine waves including: 100 x 2 = 200Hz, 100 x 3 = 300Hz, 100 x 4 = 400Hz, 100 x 5 = 500Hz, and 100 x 6 = 600Hz . . . . . .
The ratio of each of these harmonics to the others is what determines the waveform. Therefore, increasing or decreasing the amount of any harmonic will change the timbre.

Different waveforms and their harmonic components

[figure]
- how harmonic components add up to form a sawtooth wave

Taking a sawtooth wave as an example, Figure 3 offers visual confirmation that any complex periodic wave consists of a number of sine waves (the fundamental, which is of greatest intensity and lowest pitch, and harmonics or overtones which are simple multiples of the fundamental, and are of lesser intensity). "Fourier Analysis" is the mathematical method used for determining a wave's harmonic composition.


2-B  Changes in timbre ^

Most people don't pay attention to changes in timbre in the ordinary sounds they hear around them. But if someone plays a trumpet (or other brass instrument) softly, you hear a rounded sound; then if they play loudly, the sound becomes bright and sharp. This clearly shows how timbre changes in proportion to volume.

Applying vibrato to a brass instrument will also cause small variations in timbre which, in this case, are proportional to the regular fluctuations in pitch. In other words, if you make a graph of these variations in timbre, you will see the same kind of cyclic pattern as in 1-B above. Both changes in pitch and changes in timbre are easier to understand if drawn as graphs. Learn how to visualize such a graph for each of the elements that goes into a sound. This skill is important for playing a synthesizer.


3-A  Volume (amplitude) ^

When we say a sound is loud or soft, we are usually talking about its average volume, in spite of the fact that the amplitude is constantly changing. With a synthesizer, it's much more important to think about how the volume changes over time. For example, how do you really tell the difference between a flute and a piano, if they play the same note? The most obvious difference is in the way volume rises and falls. In this way, volume does not have "static" characteristics like pitch and timbre, the other two elements that determine "sound quality".


3-B  Changes in volume ^

The graphs below show the way volume changes over time for some familiar instruments:

[drum envelope]
- envelope of a drum

[piano envelope]
- envelope of a piano

[flute envelope]
- envelope of a flute

In the three figures above you can see the characteristic patterns produced as volume rises and falls during one note. Some instruments, such as the vibraphone, produce much more complicated volume changes. When you play a note on a vibraphone, you get a mixture of the single overall volume fluctuation plus a series of continuous repetitive changes. In this case, you have to analyse the sound and think of each of these volume changes in the form of separate graphs.


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