Glossary
Comb filter
Also: Comb filter effect
Definition
A comb filter occurs when a signal overlaps with a time-delayed copy of itself. Some frequencies reinforce each other, in between they cancel; the frequency response looks like a comb.
Where are the cancellations?
Link to section “Where are the cancellations?”Reinforcement occurs at frequencies whose period fits into the delay: at 1/Δt and its multiples. In between, at an offset of half a period, the signals cancel. The first cancellation is therefore at
Example: A path difference of 1.72 m corresponds to approx. 5 ms at 20 °C. The first cancellation is then at 100 Hz, the next ones at 300, 500 Hz and so on.
In PA practice
Link to section “In PA practice”Comb filters are caused by floor and wall reflections, by two loudspeakers playing the same signal at different locations and by incorrectly set delays. The delay for a path difference can be calculated.
Further reading
Link to section “Further reading”- Knowledge Phase and Interference: Why Loudspeakers Can Cancel Each Other Out
- Calculator Calculate propagation time and delay – from distance and temperature Calculates from distance and air temperature how long sound takes to travel – in milliseconds and in samples at 48 and 96 kHz.
- Calculator Calculate wavelength – with quarter wave and temperature Calculates the speed of sound, the wavelength and the half and quarter wavelength from frequency and air temperature.
- Glossary Phase Phase describes the point in its cycle that a wave is at at a given moment. A time difference Δt shifts the phase the more, the higher the frequency.
- Glossary Delay A delay holds back a signal by an adjustable time. In sound reinforcement it compensates for differences in arrival time between loudspeakers.
- Glossary Wavelength The wavelength λ is the distance between two points of equal phase in a sound wave. It results from the speed of sound and the frequency: λ = c / f.
Sources
Link to section “Sources”-
Tier B · secondary source
Wikipedia · accessed on 14 September 2026
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Tier B · secondary source
Wikipedia · accessed on 14 September 2026
Δφ = 360° · f · Δt; cancellation at 180° with equal amplitude.
Updated: 14 September 2026