How-to: Use the FM Synth

The FM Synth is an online recreation of a classic Japanese FM synthesizer. The FM Synth is an instrument doing frequency modulation synthesis. This is very different than our other synthesizers like the Simple, which is doing subtractive synthesis.

FM synthesis means that you create a complex waveform by modulating a simple waveform with another simple waveform. This is done using waveforms of different frequencies and amplitudes to kind of mangle, distort and change the sound into something more complex and interesting.

The FM Synth is quite a complex synthesizer so read on get a better understanding of how it works. We wont dig to deep here in how to use it to create complex sounds. But you can find lots of great material on FM synthesis using a search engine!

Operators and Algorithms

The DX7 have six so-called Operators. Each Operator is a sine wave and is used to create your more complex waveform. You can think of them as six different sine wave oscillators. Each of these Operators can be either a ‘carrier’ or a ‘modulator’. A carrier is something that you can hear. A modulator you cannot hear directly, instead it is used to change the tone/color/timbre of the carrier.

Whether an Operator is a carrier or a modulator is decided by the Algorithm setting. Operator number 1 is always a carrier. Then each algorithm connects the rest of the Operators in different configurations as carriers or modulators to make up your finished sound.

Here’s what the default algorithm (nr 5) looks like:

The bottom row shows the carriers while the rows above show the modulators. So in this case Operator 1, 3 and 5 are the ‘carriers’ making up the audible output of your synth. The ‘modulators’ then change the sound and timbre of each of these carriers. In this case Operator 2, 4 and 6 are the modulators.

Click here for a full view of all Algorithms.

For each Operator you can control its volume using the Out “Level”-knob. For carriers this level knob controls the output volume. For modulators however the level knob decides the amount of change it does to the carrier. And the more you turn it up the brighter the sound will be. So for modulators you can think of the level knob as something similar to the cutoff frequency in a lowpass filter.

The “Envelope” then controls the shape of this volume, for example a slow attack and long decay. The “Frequency” setting controls the pitch and harmony of the Operators.

Frequency settings

The frequency setting of each Operator decides its pitch and we have two options “ratio” or “fixed”. We control the pitch with the coarse, fine and detune parameters.

In ‘ratio’ mode the operator will follow what you play on your keyboard. With the ratio mode active the ‘course’ setting is divided into 32 steps, each equal to the “natural overtone series”. The settings represent different frequency ratios. Starting from 0 to 31, where 1 is the fundamental frequency and 0 is one octave below it.
The ‘fine’ setting divides the pitch further into 100 smaller steps, from 00 to 99. While ‘detune’ divide these up further into 15 subdivisions, ranging from -7 to +7. So the detune knob is very subtle and has a lesser effect than the fine settings.

In ‘fixed’ mode the operator will instead play a fixed frequency over the entire keyboard range. This is usually most useful if the operator is acting as a modulator.
In fixed mode you can set the frequency between 1Hz and 9,772Hz using the course and fine settings.

The Mod Setting

Use the ‘Velo’ knob to set the operators volume sensitivity to your keyboard velocity or note velocity.

Operator Envelopes

All operators have the same envelope settings. If an operator is a carrier, where the sound is routed directly to the output of the instrument, then the envelope will affect the amplitude of what you hear.
If an operator is a modulator, meaning if affects another operator, then the envelope affects the tone and timbre of the sound.

Envelopes in this synth are different than those found in our other instruments. You control the envelopes with Rates and Levels using the knobs labeled R1 to R4 and L1 to L4.

Simply put the envelope Levels are reached at different Rates. For example R1 controls how long it takes for it to reach the amplitude level of L1.

Each knob can be set between 0 and 99. For ‘Rate’ settings a high value means a fast level change and a low value means a slow level change. With the ‘Level’ knobs a high value is loud amplitudes (high levels) and a low value is low amplitudes (low levels). You can think of the Rate knob, as a speeding vehicle where 0 is moving very slow and 99 is very fast.

R1 controls the time it takes to reach the level of L1.
When the L1 level has been reached it will start to move to the L2 value at the speed of R2.
When the L2 level has been reached it will then move to the L3 level at the speed of R3.
When the L3 level has been reached it will then maintain this level for as long as you hold down a keyboard key or the length of a note. L3 here is the same as sustain in normal ADSR envelopes.
When you then release the key it will move to the L4 value at the speed of R4.

Be careful with the L4 value however for carriers as values higher than 0 means it will sustain forever. Usually this is only useful for operators that act as modulators.

Pitch Envelope

The Pitch Envelope is a global envelope used to modulate the pitch of all operators. This envelope is also of the Rate and Level type that we find in the operators, but is slightly different. Here the level knobs (L1 to L4) control the amount that it pitches up or down. The center position (50) means that there is no change in pitch. Values lower than 50 means going from or moving to a lower pitch. Values higher than 50 means going from or moving to a higher pitch. The Rate knobs once again control the time it takes to move (or pitch) between the level knob pitch values.


The Scaling part of the synthesizer allow you to create a loudness curve for each operator across the range of the keyboard. This can be used for extreme effects like split keyboard functionality. More subtly it can be used to create different loudness curves at the left and right hand sides of the keyboard. For example the curve can allow you to raise the level of one operator on the right hand side of the keyboard, which can be used to create a brighter and more harmonically rich sound in higher notes.

Rate: With the Rate scaling knob you can define the decay for each operator’s envelope depending on where on the keyboard you play. With a value of 0 the decay is the same across the full range of the keyboard. Higher values will give you longer bass note decays and shorter treble note decays.

Break: Or “breakpoint” defines the center point for the operator on your keyboard. On either side of the breakpoint you have the different loudness curves and depths.

Depth: Defines the amount of scaling for your right (Depth R) and left (Depth L) hand sides of the keyboard. 0 is the center value and depending on the curve you choose 99 will be either a positive or negative value.

Curve: Use this to set the curve type of they keyboard scaling.
0 = -LIN (negative linear curve)
1 = -EXP (negative exponential curve)
2 = +EXP (positive exponential curve)
3 = +LIN (positive lineare curve)


FEEDBACK: All algorithms in the synth will have one operator connected with a feedback loop. This means the operator output is connected back into itself and thus also modulating itself. Increasing the feedback will produce a brighter or more harmonic sound or in some cases distortion or noise.

KSYNC: Key Sync off (0) or on (1). This parameter affects all operators globally and turning it on will force all sinewaves to start in phase with each other. If it is turned off there will be slight variations with each key press which will give some tonal differences when playing.