Creator's description

4OP FM Synth


(Click to enlarge)


Version1 890kb



DSP Usage:

Very light!

Signal Flow:



47 included with the patch. Here are a few more - one for each of the different algorithms documented on the Routing page.

Samples: Here  


*** Stop Press *** 25th July 2002 - New version of the patch uploaded by Arikama. This is designed for slightly easier patch editing, and includes a number of new presets. Although the signal flow diagram does not reflect the changes made to the new version, all the text below remains relevant, and the signal flow diagram will still help in understanding the composition of an FM synth.



The original YM2151 was a chip designed by Yamaha which was used in a great number of devices from the late 80's onwards. It was used not only in several Yamaha DX-series keyboards, but also in many arcade (Taito & Sega) games and the Korg DS-8.


The YM2151 is an emulation of the chips implementation of Frequency Modulation.


Frequency Modulation is the method of synthesis in which the frequency of the sound is changed by the frequency of another sound with a frequency within the audible spectrum.  


Imagine a patch in which you are slowly modulating the frequency of a Sine wave using a slow Sine LFO. The LFO's frequency is significantly slower than that of the audible signal and we hear a familiar vibrato effect. Now imagine turning the frequency of the LFO up until it actually exceeds the speed of the audible sine wave. What happens at this point is that the modulation effect on the audible wave becomes a distortion within the individual cycles of the wave, and as a result, a great number of additional frequencies are generated and this can dramatically alter the character of the signal. Due to these extra frequencies (sidebands) generated, FM is capable of creating tones quite unlike conventional methods of synthesis. It is particularly well suited for the creation of metallic, bell-like tones, but has a great many other uses besides, as the 47 presets which come with the patch demonstrate.


Further modulation possibilities open up when it is realised that an Oscillator can be fed back to its own modulation input and modulate itself, and also that groups of more than two Oscillators can be used to create very interesting timbres. The Yamaha DX7 used 6 operators, which allowed for 32 different modulation routing configurations, or algorithms, as they are known. The YM2151+ uses 4 Oscillators which can be configured in a number of different ways. See the routing page for more on the algorithms available in this patch.


Frequency Modulation as a type of synthesis was pioneered in the 60's and rose to prominence in the 80's as Yamaha developed a number of synths relying heavily on FM as its foundation.


FM is implemented in the Pulsar Synths in both the stock FM One synth (which is an 8 (!) operator FM synth, and the separately available Poison synth, which uses a multimode oscillator and an LFO as its operators. You can read more about these in the Pulsar and Poison manuals, (get them here) both of which have an introduction to FM synthesis concepts.


For this patch, Arikama has taken the specification of the original YM2151 chip from Yamaha and recreated it in Modular form, with a few enhancements. For example, the original only had one Operator capable of self modulation, whereas the YM2151 has two. He got the information about the chip from this book:


If any of you know of an English book (or website) which has similar information about the YM2151 please let me know and I'll post details here.


More details about the patches construction, the algorithms, etc, can be found on the routing page.


For further reading on the subject of FM, I can recommend the following articles:


FM Synthesis on the Modular by Rob Hordijk. Part of the series of Nord Modular tutorials  by Rob and Roland Kuit to be found here the first section describes Fm synthesis in very clear terms. The later part of the article is more specific to the Nord Modular, but still interesting reading.


Frequency Modulation Parts 1 & 2 by Gordon Reid. Part of the Synth Secrets series for Sound On Sound, these articles are an excellent in-depth look at FM, its uses and applications. Don't be put off  by the maths in the article. If you don't 'get' the maths, you can still understand the principles of FM perfectly well. The second article goes into the different types of Modulation configurations that can be set up with multiple Operators, as demonstrated perfectly in the YM2151+ patch. See the routing page for details on how the YM2151+ has been set up to allow for different modulation paths.


The August & September 2001 issues of Sound On Sound also featured an excellent 2 part series on the history of Yamaha FM Synths, with particular focus on the DX series synths. These articles are currently subscriber only - I'll link to them here when they are available for non-subscribers.


There are a number of sites dedicated to the use of FM synthesis on chips such as the YM2151, OPL, SID, etc. Malfunction's FM Synthesis heaven is a good starting point for trackers, links, etc, while ChipTune is my personal favourite.



ym2151sitar.mp3 146kb

Here are a few snippets of the piece which Arikama posted to illustrate the patch:

YM2151_arikama1.mp3  27kb

YM2151_arikama2.mp3  61kb

YM2151_arikama3.mp3  55kb

The original piece can be found here.

Back to Top          Back to Main Patch page