Band EQ Frequency Calculator
Compute the effective frequency response of bell, high-pass, and shelf EQ bands given centre frequency, Q factor, and gain. Use it when setting up an equaliser in a mix or mastering session.
About this calculator
Equalisation shapes the tonal balance of audio by boosting or cutting specific frequency regions. For a bell (peaking) EQ band, the effective peak frequency shifts according to: f_eff = f_c × 2^(gain / (6 × Q)), where f_c is the centre frequency, gain is in dB, and Q controls bandwidth. A higher Q means a narrower, more surgical cut or boost. For high-pass and low-pass filters, the formula estimates the corner frequency as: f_eff = f_c × √Q, showing how Q affects roll-off steepness. For shelf filters, the formula uses: f_eff = f_c × 10^(|gain| / 40). These relationships help you predict where your EQ changes will actually take effect before you commit them to a mix, avoiding frequency masking and harsh resonances.
How to use
For a bell EQ boost: centre frequency = 1,000 Hz, Q = 2, gain = +6 dB. Apply the bell formula: f_eff = 1,000 × 2^(6 / (6 × 2)) = 1,000 × 2^(0.5) = 1,000 × 1.414 ≈ 1,414 Hz. The effective peak sits about 400 Hz above your set centre frequency, meaning the boost peaks at roughly 1.4 kHz — useful to know when carving space for a vocal in a busy mid-range. Adjust Q upward (narrower band) to keep the boost more tightly centred around the original 1,000 Hz target.
Frequently asked questions
What Q factor should I use for surgical EQ cuts when removing resonances?
For surgical removal of harsh resonances or feedback frequencies, a Q between 5 and 20 is typical — the higher the Q, the narrower and more precise the cut. A Q of 10 at 2 kHz, for example, affects roughly a 200 Hz band, leaving surrounding frequencies untouched. Start with a narrow Q and a deep cut (up to −12 dB), sweep the frequency to find the offending resonance, then raise the gain back to the minimum effective cut. Overly wide cuts at high Q values can introduce phase artefacts, so use them sparingly.
How does Q factor relate to bandwidth in octaves for a parametric EQ?
Q and bandwidth in octaves (BW) are related by: BW = 2 × sinh(ln(2)/2 × 1/Q) ≈ 1/Q for moderate values. A Q of 1.41 (√2) gives approximately a 1-octave bandwidth, which is a musical, broad-brush boost or cut. A Q of 0.7 gives about 2 octaves — suitable for tonal shaping — while a Q of 4 gives around a quarter-octave for precise corrections. Many DAW EQ plug-ins display bandwidth in octaves alongside Q, so understanding the relationship helps you translate between different EQ interfaces.
When should I use a bell EQ versus a shelf EQ in a mix?
Use a bell (peaking) EQ when you need to address a specific frequency range, such as adding presence to a vocal around 3–5 kHz or reducing muddiness around 300 Hz in a guitar. Bell bands are precise and have minimal effect outside their bandwidth. Use a shelf EQ to make broad, gentle tonal changes — for example, adding air to a mix with a high shelf boost above 10 kHz, or reducing low-end rumble with a low shelf cut below 80 Hz. In mastering, shelves are preferred because they alter tonality smoothly without introducing narrow resonant peaks that can sound unnatural on a wide range of playback systems.