Designing a Frequency Modulation Synthesiser in Synthmaker

Modulation VST Plug In

There are various types of  modulation based synthesis with frequency modulation synthesis being a form of synthesis that gained attention from the early 1970s onwards.

 The basic premise of FM synthesis is that a waveforms properties, are changed by applying a modulating frequency to that waveform which is in the relative audio range of the waveform.

The benefits of this type of synthesis, are that simple waveforms can be transformed into complex waveforms, offering variations in timbre and tones.

 More harmonics are produced from a simple waveform using fm synthesis, giving more depth and character to the sound.

For the purposes of creating the modulation vst effect, the basic waveforms would be two sine waves generated from a multi oscillator component. The two sine waves would provide the simple building blocks to the sound with the modulation, filters and LFO being added after this initial 1st stage.

The process involved working from the basic wave player delayed schematic. The two wave player components were replaced with a multi oscillator component running through each signal path, left and right.

Modulation effects are time domain effects. The sound properties of two sine waves can be changed when the two signal are summed together but differing time values are applied to each signal, causing phase differences between the waveforms.

This causes a change in the sound to the original waveforms, affecting the timbre and tone of the note as the waveform progresses over time. This creates the effect of phasing.

The vst being created would synthesize this effect . The two sine waves were initially summed together and routed separately through sum and delay components within which, the time properties of the signal could be altered.




basic starting point for modulation synthesizer

The difference that this makes is fairly minimal so the next stage is to affect the sine waveforms with a form of modulation. For this vst , frequency modulation will be applied to the carrier signal.

 The benefits of frequency modulation are the effect the modulator has on the sine waves. The FM modulator modulates the carrier waves frequencies, producing more harmonics and resulting in a richer sound using a minimum of components, therefore reducing cpu usage.


In order to add further interest to the sound, an ADSR envelope and LFO could be added to allow more control over the sound parameters.

 In this case, the envelope was added after the frequency modulation module. This would control the shape of the sound as it evolved over a time period.

 In this case , separate ADSR controls were added to the separate signal paths for greater flexibility in controlling each signal path with the intention of providing a wider range of sounds for the modulated synthesizer.

The next stage of the process, involved drilling deeper into the frequency modulation modules and providing some parameters and control over the frequency modulation. Control parameters would be applied to both the modulator and carrier.

control parameters connected to modulator and carrier










The most effective method of doing this, was to insert 2 vertical sliders inside each FM module, add two float integers  and then connect them appropriately within the module.

 Doing this , allows for slider control of the carrier and modulator frequencies on the front panel. For greater control over the parameters, the values of scale were also altered within the vertical sliders.

Initially, these values were entered as 20 to 20, 000 to simulate the frequency range of human hearing but some additional tweaking was performed on these values as the results produced from these settings were fairly extreme.

 One of the knobs attached to the carrier frequency on channel 2 was labelled as white noise and would be kept on the front panel as white noise can be useful in FM synthesis when simulating percussive sounds with short attack and release settings on the ADSR envelope.

After the ADSR envelope, some further refinements would be added to offer further control over the types of sounds the synthesizer can produce.

 Another section was added to the synthesizer, with the intention being to add further harmonics, generated with a sine wave form and FM modulation. The design would consist of two vector sliders, connected to float integers which would contain the values from the vector sliders. These would then affect the carrier frequency and modulation frequency of the fm module.

The vector slider would have a connection to the carrier and the other vector slider would be connected to the modulator.

This would allow some degree of change in the sound where the modulation and frequencies could be altered on the front panel independently. The FM module in this subsection linked to a sine generator and proceeded through the ADSR envelope.

This sine generator would have a switch connector which could be activated to generate further modulation between the two vector sliders. The design of this section was also based on the ideas behind FM synthesis.

 The two vertical sliders would have to be set at 0.00 in order to have no effect on the output sound at all. When the vector sliders are moved from the 0.00 position, some higher harmonic content is added to the existing sound.

 A small LED switch was added allowing the option of switching the oscillation sub section on and off when desired.

 Due to the complex harmonic material inherent in the FM synthesis design, it was decided to add a visual representation, enabling the user to quickly visualize the nature of the harmonic content.

This was done by adding an FFT scope for analysis purposes. When adding the high harmonics with the vector slider, it is clear on the analysis display on the front panel where the harmonics occur.

A simple ping pong delay was added before the strength and volume control sections within the synthesizer. This was a simple design with customized controls, intended to create some interest in the movement of the sound without being too extreme.

Within the volume and strength controls section of the synth, some manual adjustments would be made to the integer values within the bender module as well as the adjustments to the scaling of the volume and strength controls. The adjustments to the volume and strength controls were ,again, performed by drilling into the controls and setting the minimum and maximum levels as appropriate so as not to clip the out puts.

 The final component part to add, was the preset manager which would provide some quick presets for users to get started with.

To finish of the vst plug in, the controls were arranged in a coherent manner on the front panel with each function and control being clearly named and a clear separation being provided between the sections of the synthesizer. Some adornments were added to enclose the separate sections and some simple colour schemes were also introduced for a clear cohesive front panel layout.

For the new Ppas St Germain sample pack Ambient Electronica Vol 1, FM synthesis was used quite frequently.Fm sounds can be effective for some styles of ambient and chillout genres,adding some edge and fizz to otherwise placid sounding synths.

I think this gives the sounds more character

Ambient Electronica available at sampleism.com from Feb 12th 2015