EQ Frequency Calculator
Find the target frequency after shifting a center frequency by a given number of semitones or octaves. Essential for EQ matching, filter placement, and harmonic tuning in mixing and mastering.
About this calculator
In audio engineering, frequencies are spaced logarithmically, meaning each octave represents a doubling of frequency. To shift a center frequency by a fractional number of octaves (expressed in semitones), the formula is: targetFreq = centerFreq × 2^(octaves / 12). Here, dividing octaves by 12 converts semitones to octave fractions, since one octave equals 12 semitones. For example, moving up one full octave (12 semitones) from 1000 Hz yields 2000 Hz, while moving up 7 semitones (a perfect fifth) yields approximately 1498 Hz. This relationship is the same equal-temperament tuning system used in musical instruments and is critical for aligning EQ bands with harmonic content in a mix.
How to use
Suppose you want to find the frequency 5 semitones above a 440 Hz center frequency. Enter 440 in the Center Frequency field and 5 in the Octaves field. The calculator computes: 440 × 2^(5/12) = 440 × 2^0.4167 = 440 × 1.3348 ≈ 587 Hz. This is the note D5 (approximately), useful when you want to boost a harmonic fifth above your fundamental. Try entering 1000 Hz with 12 semitones to confirm you get exactly 2000 Hz — one clean octave up.
Frequently asked questions
How do I calculate the frequency one octave above or below a given frequency?
To find the frequency one octave above, multiply your center frequency by 2. One octave below means dividing by 2. Using the formula targetFreq = centerFreq × 2^(octaves/12), entering 12 semitones gives exactly double, and entering -12 gives exactly half. For example, one octave above 500 Hz is 1000 Hz, and one octave below is 250 Hz.
What is the difference between octaves and semitones in EQ frequency calculations?
An octave represents a 2:1 ratio in frequency — each octave up doubles the frequency. A semitone is 1/12th of an octave, the smallest standard musical interval in Western equal temperament. When working with EQ, bandwidth is often described in octaves (e.g., a broad 2-octave boost), while pitch relationships are described in semitones. The formula bridges both by dividing semitone count by 12 before raising 2 to that power.
Why are EQ frequencies spaced logarithmically rather than linearly?
Human hearing perceives pitch on a logarithmic scale — we perceive the jump from 100 Hz to 200 Hz as the same musical interval (one octave) as the jump from 1000 Hz to 2000 Hz. A linear scale would crowd all the musically important low frequencies into a tiny portion of the display. Logarithmic spacing matches how we experience sound, making it far more intuitive to place and adjust EQ bands at musically meaningful points in the frequency spectrum.