Expert: Cleggsan - 7/27/2009

Question
Hi:

What is the difference between AFM [Advanced Frequency Modulation] synthesis and FM [Frequency Modulation] synthesis?

The former is used by synths like SY99, SY77 and TG77. The latter is used by synths like OPL3.


Thanks,

Green

Answer
This is a really good overview of FM synthesis:

http://en.wikipedia.org/wiki/Frequency_modulation_synthesis

Mathematically, one of the key factors in FM is the generation of Bessell functions.  These provide for a very interesting bending of a sine wave and its harmonic structure by altering the beta function.

AFM or Advanced FM is a variation on FM which adds multiple modulators to a sine wave.  It seems to have been invented and employed by Yamaha and then adapted in other ways by competitors.  

http://en.wikipedia.org/wiki/Yamaha_SY77

Above is a good explanation of their system.  Mostly, the synthesizing is done by digital tone generation and modulation.  Sample sounds are used as a reference form which to build sound profiles or patches.

Both of these systems are centered around the MIDI solutions for small data files for creation of complex sounds.

You should also study the invention called Csound from MIT and developed by Dr. Barry Vercoe of the MIT Media Lab.  It is a synthesizing system basic on C program codes and once profiles are written it can synthesize any type of sound from human voices to choral and musical instruments, etc.  The most successful use of Csound is for advanced Karaoke systems in Japan by Taito.

Hope this is helpful for you.
C