Sound & signal
Filter types
Filters differ by which part of the spectrum they remove. High-pass and low-pass cut one end, band-pass keeps a middle slice, notch removes a narrow sliver, and a shelf lifts or drops everything past a point.
In practice
Your mixer knob is high-pass and low-pass. Notch fixes a ringing room; shelves are what your EQ actually is.
Use band-pass to make a record sound like a telephone into a drop, and notch only when hunting a specific problem frequency — a feeding microphone or a room resonance. Remember that a mixer’s high and low EQ are usually shelves rather than bands, so cutting the highs takes everything above the crossover with it. That is why a "hats only" effect needs the filter rather than the EQ.
HP / LP
What the mixer knob does
Notch
For a ringing frequency
Shelf
What your EQ actually is
Where these come from: Standard filter topologies and DJ-mixer EQ design — conventional, not catalog figures. For what we can measure, see the one on your mixer.
Why it matters
DJ mixers give you one filter knob that sweeps between high-pass and low-pass, so most DJs only ever meet two of these. Knowing the others matters when something is wrong rather than when you are performing — a ringing frequency needs a notch, and no amount of sweeping the mixer filter will find it.
The shelf is the one hiding in plain sight: the EQ on most mixers is shelving at the top and bottom, which is why a full high cut removes everything above the crossover rather than just the hats. That is a different behaviour from an isolator and worth knowing before a transition depends on it.
Frequently asked
What is a notch filter for?+
Removing one narrow frequency — a ringing room mode or a feeding microphone. It is a repair tool rather than a performance one.
Is my mixer EQ a shelf or a band?+
The high and low are usually shelves and the mid is a band. That is why a full high cut removes everything above the crossover rather than just the hats.
What does band-pass sound like?+
A telephone or a radio — everything above and below a middle slice removed. It is a strong effect into a drop and tiring over any length.
Related terms
Filter
A filter removes everything above or below a moving cutoff point. A high-pass strips the bottom away as you turn it up; a low-pass takes the top off as you turn it down.
Resonance
Resonance boosts the frequencies right at a filter’s cutoff point, so the sweep sings rather than simply removing content. Turned far enough up it can self-oscillate into a tone of its own.
Cutoff
Cutoff is the frequency where a filter starts acting — everything above it on a low-pass, everything below it on a high-pass. Moving the cutoff is what a filter sweep actually is.
Three-band EQ
A three-band EQ splits each channel into low, mid and high and gives you a knob for each. It is the primary tool for deciding which parts of two records are audible at any moment.
Explore: Frequency detector · Filter · Isolator · All DJ terms