First, let us introduce outline of FM tone generation system and the related terms. FM tone generator incorporates two or more oscillators, producing sounds by combining their outputs or modulating one oscillator with the output of another to alter the output waveform.

In FM tone generation systems, an oscillator is called "Operator," while a configuration of operators is called "Algorithm." An operator modulated by another operator is called "Carrier," while an operator that modulates another operator is called "Modulator."

Algorithm where two operators are vertically linked, one work as Carrier and the other as Modulator, would be an example to help you understand how Frequency Modulation creates sounds. Output of Modulator is sent to the Carrier; only the output of the Carrier is audible.

The increase in the volume of the Modulator modulates the frequency of Carrier according to volume level and alters the output waveforms in real-time. When more modulation is applied to the Carrier, more overtones are produced, which result in brighter and harder timbre, and finally timbre like noise. In short, tonal brightness can be controlled using the output levels of modulators.

MA Sound Demo061 demonstrates the process to control output levels of modulators. The sound of Operator that is not modulated will be changing gradually by increasing the output level of the modulators and increasing the overtones to be a noise finally.

Another important parameter that determines timbre is frequency ratio of the carrier to the modulator. The type of overtones depends on the ratio of the frequency of the modulator to the frequency of the carrier. In short, the frequency ratio determines the characters of waveforms.

When the frequency ratio is 1:1, sound will be something like horns and strings. Frequency ratio of 1:2 produces the sound like instruments such as a clarinet. When the frequency ratio is higher, the more overtones are produced in the high frequency range, which are apart from fundamental pitch and eventually be making metallic tone. In MA Sound Demo062, the frequency ratio varies from 1:1 to 1:2, 1:3 and more, with the consistent output level of the modulator. Understanding characteristics of the sounds produced at each frequency ratio is required to learn how to create sounds using an FM tone generator.

You have learned the type of overtones was determined by the Carrier to Modulator frequency ratio, and that the volume of overtones was determined by the Modulator output level. Let add movements to the sound by using the envelope generator of each operator. The modulator's envelope generator can control the changes of timbre, and the carrier's envelope generator can control changes of sound volume.

MA Sound Demo063 demonstrates the process of creating a synth brass sound by adjusting the envelope parameters. MA Sound Demo064 demonstrates the process that some types of sounds, from a marimba to a bell, are created by adjusting the envelope and frequency ratio.

In FM tone generation systems, more number of operators allows users to apply more complex modulations or overlay two or more timbres, for greater sound programming flexibility. MA-2 and MA-3 sound chips output different waveform types in addition to sine waves, enabling even a small number of operators to achieve similar effects. Even with one operator, strong modulation can be realized, and creating sounds by synthesizing waveforms without modulating can be realized. In MA Sound Demo065, the waveforms of the modulator are changed, one waveform after another with fixed frequency ratio of Carrier/Modulator and output level of the modulator.