Quiz Post: Frequency Modulation

I got less than a 80% on the quiz, so I am posting an in depth explanation of one of the questions that I got wrong, which in this case is frequency modulation.

Frequency Modulation Synthesis (FM synthesis) is a form of audio synthesis where the timbre of a simple waveform is changed by modulating its frequency with a frequency that is also in the audio range. This results in a more complex waveform and a tone that sounds "gritty" if it’s a dark and thick timbre. The algorithm for creating this type of modulation was created by John Chowning at Stanford University in 1967. It was patented in 1975 and later licensed to Yamaha. Five years later, Yamaha released the DX-7 keyboard synthesizer, and it was extremely popular. FM synthesis can make both harmonic and inharmonic sounds. This depends on the amount of frequency modulation that is used. FM synthesis is often used to make noises that sound like bells and percussion instruments. FM synthesizers using analog oscillators became somewhat obsolete when it was discovered that FM synthesis can be implemented digitally (in fact, digital FM synthesis was the inspiration for Yamaha’s DX-7 keyboard synthesizer). This is because FM synthesizers using analog oscillators often resulted in pitch instability.