What is FM synthesis?
FM synthesis stands for frequency modulation and is created by taking one waveform and cascading it into another waveform. One waveform modulates the pitch of the other. Each waveform is referred to as an ‘operator’ and each operator performs a different role in FM synthesis. The first operator in the chain is known as the ‘modulator’ because the parameters of this operator can greatly effect the tonal qualities of the other operator, known as the ‘carrier’.
- The operator that does the modulating is known as ‘the modulator’
- The operator that is being effected is the carrier. This is the main ‘output’ that the listener hears. The carrier is also the ‘modulation destination’.
In FM synthesis, there are two important factors that shape the tone of the carrier.
- The frequency of the modulator compared to the carrier.The higher the pitch of the modulator, in comparison to the carrier, the brighter the tone will be
- The depth of the modulation will determine the extent to which the carrier is modulated.
The depth of the modulator is often controlled over time with an envelope to create tonal shifts.
There is no particular waveform that needs to be used in FM synthesis but, sine waves are much more controllable than other waveforms such as: square waves, triangle waves, sawtooth waves and random waves. In this case, a sine wave was selected in both the ‘modulator’ and the ‘carrier’.
Shaping the tone
The output that the listener hears is the result of the ‘carrier’ being affected by the ‘modulator’. The tonal characteristics created during this process can enhanced by:
- Increasing the sustain of the ‘modulator’. This results in the output increasing with a noticeable shift in tone.
- Controlling the output of the modulator is best done by using an envelope filter. This is placed in between the ‘modulator’ and the ‘carrier’.
- Raise or lower by semitones:
- the pitch of the ‘modulator’
- the pitch of the ‘carrier’.
Usually the pitch of the ‘modulator’ and not the carrier, is raised and lowered. This greatly affects the overall tone of the waveform produced during FM synthesis.
Another method of FM synthesis in the studio is achieved by pre-set algorithms found in some software or hardware. Parameters can also be manually adjusted to produce a great variety of contemporary bass tones used by Skrillex ( Skrillex In Conversation With Jeff Rosenthal) & Kill the Noise (UKF Meets – Kill The Noise).
The following synthesizer patch was created using a software instrument within Ableton called: Operator. Ableton is a premier piece of software that is used by electronic music producers in both live and studio settings. A number of images were taken from the session in Ableton and appear below to demonstrate the parameters mentioned above.
The first thing to notice is that on the left hand side of the operator window, only the ‘A’ and ‘B’ synthesizers have been enabled. This experiment was designed to test the theory of FM synthesis using the sequence of: ‘modulator’, envelope filter ‘carrier’. Sine waves were used to manage the sound better than other waveform types.
The LFO has also been enabled on the ‘modulator’. Notice also that the ‘key’ has been set in the middle window to 30% on the ‘modulator’ and 60% on the ‘carrier’. This tests the theory that altering the pitch (or ‘key’ in Ableton) of the modulator, can produce a great variety of tones. There has also been an envelope filter placed in-between ‘the modulator’ and the ‘carrier’ to enhance the tonal qualities and greater depth of the final FM synthesizer patch.
You can listen to two examples of the results of this experiment below.
Synthesizer Boot Camp. (2017). YouTube. Retrieved 25 August 2017, from https://youtu.be/7XJVMd-HhAo?list=PLN5UCK4omWX0VvC-5ASJ55bMWS5oUHmpi