Frequency modulation is a technique of signal processing in which the instantaneous frequency of a higher-frequency carrier signal is varied in proportion to the amplitude of a lower-frequency modulating signal: the carrier's phase continuously accumulates the integral of the modulating signal, so the information rides on frequency variation rather than amplitude variation. For a sinusoid modulator the output contains the carrier plus sideband pairs at f_carrier ± n·f_modulator for every integer n (Bessel expansion), with occupied bandwidth given by Carson's rule, ≈ 2(Δf + f_max). Its parameters are the peak frequency deviation Δf in Hz, the modulating frequency, the modulation index Δf/f_modulator, and the carrier frequency. The persistence mechanism: analog FM realizes it in a voltage-controlled oscillator whose control input tracks the modulating signal; digital FM accumulates a per-sample phase increment in a phase accumulator and synthesizes the carrier from it; and it persists institutionally as the operating standard of FM radio broadcasting (87.5–108 MHz) and two-way and marine radio, and as a synthesis engine in audio (Chowning's FM synthesis, 1973). [formal: modulatio frequentiae | substrate: mind | horizon: a moment | explicit: yes | epoch: 0.12]
Accepted ontology entry
frequency-modulation
Frequency modulation is a technique of signal processing in which the instantaneous frequency of a higher-frequency carrier signal is varied in proportion to the amplitude of a lower-frequency modulating signal: the carrier's phase continu…
Definition
Why it is in scope
A human-made signal-processing technique: the operating principle by which FM radio broadcasting, two-way radio, and FM synthesis modulate a carrier, built to persist as a mathematical relation and as engineered oscillator hardware and software.
Names and aliases
- frequency-modulationen · CANONICAL
Relations from this entry
- modulationINSTANCE_OF →
Frequency modulation is a member of the modulation family whose varied carrier property is frequency: modulation's accepted definition carves "varying one or more properties of a carrier signal (amplitude, frequency, or phase)," and FM is exactly the frequency case, with its parameters (deviation, modulation index) as the family's parameters specialized to frequency. A competent speaker calls FM "a kind of modulation," so the specific points at the general (Law 9). Pinned sense is the family sense the target's own definition carves (Law 11d); nearest kind is modulation itself — the accepted sibling rung AM→modulation shows no intermediate rung exists (Law 11e). Direction tested: FM is the specific, modulation the general.
- audio-effectINSTANCE_OF →
Frequency modulation is a specific kind of audio effect: it intentionally alters a sound signal by varying instantaneous frequency, fitting the audio-effect carve. Nearest kind per Law 11e.
Relations to this entry
- vibrato← INSTANCE_OF
Vibrato is a specific kind of frequency modulation: a low-frequency oscillator (the modulating signal) varies the instantaneous frequency of the sound source (the carrier) in proportion to its amplitude — exactly the carve in the target's accepted definition ('the instantaneous frequency of a higher-frequency carrier signal is varied in proportion to the amplitude of a lower-frequency modulating signal'), which explicitly covers the synthesis use case ('as a synthesis engine in audio'). A competent synthesist calls vibrato 'an LFO on the pitch input' — i.e., FM by an LFO. Nearest kind per Law 11e: frequency-modulation is more specific than audio-effect or modulation, and no intermediate rung is filed; this is the direct twin of the filed tremolo INSTANCE_OF amplitude-modulation edge (frequency case vs amplitude case of the LFO definition's two named uses). Direction tested: vibrato is the specific, FM the general (Law 9).
Record identity
- Created
- Sep 6, 2026, 5:14 PM UTC
- Content hash
- 6445d25607b0ee3d53ad6d0fd021b91f553c2801e2ae9e4dd3db2780202ea24a