Why are shelves used at the ends and a peak in the middle?

Because the useful question about the extremes is how much weight or air the recording has overall, which a shelf answers in one control, while the midrange holds specific problems that a broad peak can address without disturbing the bands on either side of it.

Why is the middle band so wide?

A Q of seven tenths is deliberately broad. A narrow peak is a surgical tool for cutting one exact frequency, whereas this control is meant to change the character of the middle rather than to remove a single tone, so it takes a wide slice of the range.

Does moving one band affect the others?

Slightly, because the three filters run in series rather than being summed. That is normal for an analogue-style tone stack rather than a fault, and the corner frequencies were placed far enough apart that each band's main effect stays in its own range.

Should I boost or cut?

Cut where you can. Taking a couple of decibels out around a kilohertz removes muddiness without adding energy elsewhere, while boosting raises the level and can push the output toward clipping. The panel says the same thing: subtraction usually sounds cleaner than addition.

Can I remove the very low end entirely?

Not with this tool, which has no high-pass filter; a twelve decibel cut at the bottom is available, but it is a shelf rather than a removal. The telephone effect, the underwater effect and the vinyl record effect all high pass their input, at different corner frequencies.

Equalizer / 3-band EQ

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Audio Limiter

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Equalizer is the classic three-band tone stack: a bass shelf, a midrange peak and a treble shelf, each with twelve decibels of movement in either direction and a fixed corner.

What is Equalizer / 3-band EQ?

Drop a file, move the three bands, and apply; the filters are chained in a fixed order and each one can move twelve decibels either way, with the default flat.

The three bands:

Bass, a low shelf turning over at two hundred hertz, so everything below that point moves together as a block.
Mid, a peaking filter centred on one kilohertz with a Q of seven tenths, which is broad enough to colour a range of frequencies rather than a single note.
Treble, a high shelf turning over at four kilohertz, which lifts or drops everything above it.
Each band runs from twelve decibels of cut to twelve decibels of boost in single decibel steps, and the report repeats the three figures with their corner frequencies. Each band is one biquad section.

The choice of filter shapes is what makes the layout behave like a mixing console rather than like a graphic display. Shelves are used at the two ends because that is how the ear hears the extremes: the useful question about the bottom is how much weight the whole low end has, and about the top how much air the recording has, and a shelf answers both with a single control rather than making you draw a shape. The middle band is a peak instead, because the midrange is where specific problems live — a boxy resonance, a nasal honk, a dull patch — and a peak with a moderate Q can lift or drop one region without disturbing the neighbouring bands. The Q of seven tenths is deliberately wide: a narrow peak is a surgical tool for removing a single frequency, while this control is meant to move the character of the middle, so it takes a broad slice of it. Because the three bands are chained in series rather than summed, moving one slightly affects the response where the next one acts, which is exactly how an analogue tone stack behaves and why the corners were chosen to overlap as little as possible. The measurements confirm the filters do what they claim: a full twelve decibel shelf boost lands within half a decibel through the passband, and the bands left at zero are left untouched rather than merely barely changed.

Where it is limited:

Three fixed bands, with no sweepable corners or additional bands.
No per-band bypass and no dynamic behaviour, so the response is the same at every level.
No spectrum display to see what is being changed.
No high-pass or low-pass filtering for removing the extremes outright.
No presets, so the settings are yours to choose.
Output is sixteen bit WAV.

Use it as a general corrective and creative tone control: taking out a muddy middle, adding weight to a thin recording, or taking the edge off something bright. The panel's own advice is worth repeating, that cutting around one kilohertz by a couple of decibels usually sounds cleaner than boosting anything, because a subtractive move leaves the rest of the balance intact. When a single low end needs lifting by a controllable amount, the bass booster is a shelf with a movable corner, and when the problem is an unwanted frequency band rather than a tonal balance, the notch and high-pass shapes in the hum remover and the telephone effect are the right tools.

How to use Equalizer / 3-band EQ

Drop an audio file onto the panel and let it decode.
Start by cutting rather than boosting, usually a couple of decibels around one kilohertz.
Move the bass and treble shelves to set the overall balance.
Apply the EQ and compare against the original before exporting the WAV.

When to use Equalizer / 3-band EQ vs related tools

Equalizer is the tool for shaping the overall balance of a recording with three broad controls. Bass Booster generalises the low band with a movable corner and a larger range, and Hum Remover takes out a specific interfering frequency instead of a region. When the tone change should imitate a device rather than correct a balance, Radio Effect and Telephone Effect impose a band as part of their character. For the band that a hearing aid actually amplifies, Hearing Aid Frequency Reference is the reference to work from.

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