Comb Filter Notch Frequency Calculator | See Cancellation and Reinforcement Bands
Move one delay-time slider and read the first six comb-filter notches and the first six peaks at once. The equivalent path-length difference at 343 m/s shows up in centimeters and inches, so you can tie a microphone spacing or a reflection distance straight to the frequencies it kills.
💡 About this tool
When the same sound reaches an output through two paths a fraction of a millisecond apart, some frequencies cancel and others pile up. That is comb filtering, and it is why a take can sound thin, hollow, metallic, or "phasey," as if chunks were scooped out of the spectrum. It hides everywhere on a session: spaced overhead pairs, a backup mic bleeding into a vocal, an early reflection off a console or wall, two line-array boxes overlapping in the room.
The hard part is that delay time and missing frequency are not intuitively linked. Enter a delay and this tool lays out the notch series at (2n−1)/(2τ) and the peak series at n/τ. Sum mode is the plain case where two mics simply add; diff mode is the polarity-flipped case where the notches and peaks swap places — exactly what happens the moment you hit a polarity switch. Rows above 20 kHz are dimmed so you only chase what an ear can actually hear.
The path length is the delay translated back into distance through the speed of sound, which lets you reason in inches: "how much farther do I move this mic to push the first notch up out of the way?"
🧐 Frequently Asked Questions
Where is the first notch at 1 ms of delay? In sum mode it lands at 500 Hz, then 1.5 kHz, 2.5 kHz, spaced by 1/τ (1 kHz here). Shorter delays widen the spacing and push the first notch higher.
Why do the notches and peaks swap? Diff mode means one of the two signals has flipped polarity. With the phase inverted, frequencies that used to cancel now reinforce and vice versa. Hitting a mic preamp's polarity button produces exactly this swap.
What distance is the path length? Delay time times the 343 m/s speed of sound — the difference in path length between the direct and the delayed (or second-mic) arrival. For a spaced pair it gives you a number to sanity-check against the 3:1 rule, where the far mic sits at least three times the near distance.
At what delay does comb filtering get audible? As a reflection nears 10 ms the notches drop into vocal fundamentals and become obvious; past about 35 ms the ear starts hearing the reflection as a separate event. The 0.02–50 ms range straddles both edges.
Does this run only in the browser? It computes frequencies from the delay you type — nothing is uploaded. It is a design calculator for notch and peak positions, not an audio-file analyzer.
📚 Why It Is Called a "Comb"
Plot the frequency response and the evenly spaced notches line up like the teeth of a comb — hence the name. A fixed delay gives evenly spaced teeth; change the delay and the teeth stretch or bunch. The studio "3:1 rule" leans on distance, not on this math: put the far mic three times the near distance away and the delayed copy arrives roughly 10 dB quieter, which makes the teeth shallow enough to ignore. Read notch position here, manage notch depth with distance, and on-the-spot decisions get faster.