From BeepBox Wiki
FM as seen in BeepBox V2.3. It originally included four operators and an algorithm selector.
FM as seen in BeepBox V2.3

FM, also known as Frequency Modulation, is an instrument type that uses a set of four or six operators arranged in an algorithm to create a sound. An operator can be used to generate an audible sound or modulate the frequency of another operator. Due to the nature of FM, it can be used to make various sounds whether instrumental or percussive. The FM made its first appearance in BeepBox update V2.2.3.


Uses four operators which are all sine waves, each with volume bars and frequency selects for each operator, and two select boxes for choosing the algorithm and feedback.

GoldBox FM

Same as the normal FM, but each operator can have a unique waveform other than just sine waves, allowing the usage of pulse widths, triangle/sawtooth waves, etc. per operator and allowing many more possibilities. In the case of the pulse width operator waveform, it also comes with a pulse width slider of its own.

SynthBox FM

Same as the normal FM but uses six operators and many more algorithm/feedback patterns.

Advanced FM

Combination of all FMs. It uses six operators, with each operator being able to have waveforms other than sine waves, and allows the creation of custom algorithm and feedback patterns by utilizing its UI.


All FMs support the custom interval chord type, but do not support anti-aliasing or unisons.

In Dogebox2, FM (specifically GoldBox FM) is also supported in drum channels.