Fm Synthesis Simulator

With this widget, you can change sidebands in real-time while exploring how frequency modulation synthesis works. Click on the pitch pads to play it with your mouse or get hands-on by using your computer keyboard.

There are four sections: Performance Keys; Parameter Controls; Spectrum Visualization, and Operator Coupling. Four big pitch pads is in the performance section below that. When you click on one of these pads it will play a note. There is one for A3, C3, A4 and C5. You can also use the keys on your keyboard and then Z, X, C and V respectively if that’s more comfortabley for you. Then the tone just keeps sounding as long as you hold down the key.

How to Use the Sound Widget

The main synthesis parameter sliders is located between the operators. Carrier tune controls the base frequency from 80 Hz to 880 Hz. You will hear this when the modulation index is zero. Ratio buttons allows the modulator frequency to be locked with the carrier. Ratios such as 1 and 2 will produce harmonic tones. Other ratios such as 0.5 or 1.5 give metallic, inharmonic sounds Another control lets you adjust the amount of modulation applied to the carrier using the modulation index slider. A lower setting maintains a pure bell-like tone. Increasing the index scatters energy out into higher and lower frequency bands (sidebands), producing rich dense sound texture.

You can select from two types of modulator waveforms: triangle and sine. Selecting the triangle wave shape adds more harmonics to the modulation signal, which creates more aggressive, grainy sounds.

There are three pre-sets on the sideband atlas. To select one, just click on it to load that specific set of waveforms, index, and ratio. The first is a clean compact bell type tone from the electric tine focus. The second is a dense inharmonic wash from the tubular alloy fan. And the third is a grittier, low sound using a triangle wave. These are great starting points to get a feel for how the parameters work together.

What You Get: The spectrum panel visualises the sound. The top shows frequency components, where the height of the bars represents the relative loudness of each sideband. The bottom tracks the waveform, allowing you to observe how the modulation affects the carrier wave. As you adjust the ratio or tweak the sliders, the visuals update immediately so you can easily see what’s happening and why.

The flight deck buttons provides automation. A press of one of these buttons will automate the Modulation Index, ramping it up from zero to maximum and back in six seconds. This means you do not need to touch any controls as you listen to the changing spectrum from pure to complex. Ground stops all voices instantly, handy if you wish to stop a sound cleanly. Reset puts all parameters back to their default state.

Use your keyboard: Press F to launch the modulation index flight, or press P to page through the atlas patches one at a time. If any of the slider controls have focus, use your arrow keys to adjust them. To halt the sound and bring the operators back to earth, simply press Escape. Experiment fast, but keep your fingers on the keys.

There’s also a volume slider for setting the total output level. Don’t set it too high if you use these with high modulation indices, as they can create many loud sidebands. Finally, the bottom status bar gives some feedback based off the state of the widget: Are there any flight sequences active? Which operators are currently coupled?

To demonstrate this, try selecting a note then gradually drag the modulation index slider. Notice what happens to the spectrum display as you increase the index. Watch how new peaks appear in the spectrum display as the index rises. If you experiment with different ratios, you’ll hear how the spacing of the frequency peaks changes. The shimmering and beating sounds we associate with certain sounds are produced by uneven rather than integer ratios.

Keep the index and ratio the same but vary the type of modulation: sine, triangle. Listen to how the addition of a triangle wave brings some roughness and density into the tone. The reason is that the triangle wave has higher harmonics which are then modulating the carrier. You can hear this in the spectrum with the addition of more components.

Use the pitch pads to hear how the same synthesis settings translate across different fundamental frequencies. An A3 tone may be tubular or metallic sounding compared to one played at C5. This gives a look into how FM works at the scale of pitch.

You can use a bigger workspace with the widget’s fullscreen mode. To enter it, click on the fullscreen button located in the top right corner of the interface. You’ll get a bit more space to work with the controls and see the spectrum details. Press Escape or click on the same button again to exit fullscreen.

For instance, the how to play button is there if you want to refresh your memory on the controls. Click it and it opens up a control panel with brief directions about what each key does and how it’s mapped to the keyboard. This way, if you go back to the widget later and forget, you have the quick reference handy. The control panel is short and just covers things that are important.

First load an A3 pad and hold that, then load the electric tine patch and dial back the modulation index and hear what happens. Next, load the tubular alloy patch and move up on the index and watch the spectrum fill out. Spend some time with the parameters; each combination has its own sonic character.

The interface is responsive and easy to use. The sliders respond instantly as you make changes. The visuals follow right away. There’s no need to click another button to apply them. They happen immediately so you can experiment freely.

You can use the keyboard/mouse combo too. With one hand, hold down a note on the keyboard (Z) and then tweak the ratio up or down using the number keys. While the pitch stays the same, this allows you to listen to the change in tone as you change the harmonic relationship between the two notes. This is a fast method for comparing synthesis recipes.

Keep in mind, higher modulation indices result in some very complex spectra. You may wish to reduce the index and/or use a different modulator like the sine wave if it’s getting too grating on your ears. Also note that triangle modulator has the potential for quite a bit of high frequency content. Bring down the volume slider if required to maintain a pleasant listening experience.

The widget calculates sideband amplitudes using Bessel functions for sine modulation, while it analyzes the frequency trajectory for triangle modulation. It’s mathematically precise so the visual spectrum corresponds to the sound you’re hearing. Graphs aren’t just decoration; they correspond to the actual audio content.

And then there’s the reset button. It resets everything back to center on the sliders, clears out any currently running patches, and gives you a clean slate. It is a good habit to get into when starting a new sound design project. This gives you a starting place so you know where to begin.

Try out the flight feature on each of these patches. The sound changes over time. Listen for the appearance/disappearance of the side bands as you change the index. This helps you understand how FM synthesis changes.

Keyboard layout is straightforward with little memory required. Short phrase fingerings group on the keys: Z-X-C-V. Ratio keys are near-by too on the number pads. It’s a great way to work that helps you be efficient as you explore.

Notice the present reading on the control deck? That’s a description of what the signal is like. How dense is it, how close to pure carrier is it? That will help you find where on that parameter space you are. You can hear it in action and see the strongest line and other sound components in the spectrum panel. From here you have a quick overview of what’s going on with the frequency content. How much energy is there at the fundamental and how much is spread across multiple harmonics. It helps with the balance of the tone too.

The widget responds well on varied screen sizes. All the controls remain available and the layout adapts accordingly. Try using it on a bigger tablet or even a desktop computer. Touch targets are sized comfortabley so you can interact with the instrument easily.

For those who like to navigate by keyboard, just tab around until you have each control focused then move sliders with the arrow keys. This allows very precise control of parameters. This is great for when you find a patch that you want to fine tune.

There is some useful info in the help panel too. There are some conventions to be aware of regarding the display. It explains how the height of the sidebands is calculated. Some components aren’t shown for clarity. Knowing this can help you understand more from what you see.

Have fun and start making sound. With waveform, index, and ratio combinations it seems endless. Every time you tweak one setting another facet of frequency modulation appears. Have fun discovering things.