Parametric EQ

• Filter
• Since 0.2.0
• eq
• equalizer
• filter
• tone
• shelf
• bell
• notch

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An editable list of up to 32 bands for tone shaping in one node: cut the rumble, tilt the ends, boost or carve the middle, and remove a single ringing frequency.

What it does#

Each band is one biquad filter from the RBJ Audio EQ Cookbook, run in canonical ID order, then the Output trim. A band has a switch, a type, a frequency, a gain and a Q. Low cut and High cut remove everything below or above the frequency at 12 dB per octave, with Q as the resonance at the corner. Low shelf and High shelf raise or lower everything below or above the frequency by the gain. Bell boosts or cuts a region around the frequency, and Notch removes a narrow band entirely. A band that is off is bypassed exactly, and every channel of the cable gets its own filter state. Frequencies are capped at 0.49 times the sample rate.

The node card draws the summed response over each band's own curve, with one point per band in its own colour. Drag a point across for frequency and up or down for gain; on a cut, up raises Q. The wheel over a focused point sets Q, and double-click resets it. A clicked point keeps its band's region lit until the pointer leaves that region. Double-click empty space on the curve to add a Bell band at that frequency and gain as one Undo step. Bands can also be added, folded, reordered and removed on the card and in the inspector. Drag a grip beyond the card to remove a band; at least one band remains. Reordering preserves each band’s controls, cables and colour and keeps audio playing. While a Toy plays, the face you are working on draws the output spectrum under the curves.

Hold Alt (Option on a Mac) with the pointer over a band's point, or inside the region of the band you clicked, to solo that band: you hear only its region, and the screen says "Solo band N". A bell or notch solos as a band-pass at its frequency and Q; a low cut or low shelf as a low-pass at its corner, and a high shelf or high cut as a high-pass. The solo plays at the input's level, without the Output trim, and fades in and out over 5 ms. Release Alt, move off the band or press Escape to stop. Soloing is for listening only: it never changes the Toy, its undo history or anything saved.

When to use it#

Use it to fit a sound into a mix: take low end out of a pad, add air to a lead, dip a boxy middle, or notch out a hum. For a resonant sweep or a morphing filter use the Filter; for one gentle roll-off use the Low-pass filter.

Ports#

Parameters#

• bands: 1–32 items, each with a durable id and optional name, color, icon. Item order affects presentation only; ports and controls use the item ID.

Band switches (band.enabled)#

Turn a band on or off. Bands 1 and 6 start off, so the default EQ is flat with every band ready to use. An off band leaves the signal untouched, and when it comes back on it starts from rest.

Band types (band.type)#

Low cut, Low shelf, Bell, Notch, High shelf or High cut. Any band can take any type; the defaults run from a low cut on band 1 to a high cut on band 6.

Frequencies (band.freq)#

The centre of a bell or notch, or the corner of a shelf or cut, from 20 Hz to 20 kHz on a logarithmic control.

Gains (band.gain)#

Boost or cut in dB, from −24 to +24, for shelves and bells. Cuts and notches have no gain, so it is hidden for them.

Q (band.q)#

From 0.1 to 18. On a bell or notch, higher Q is narrower. On a cut, Q is the resonance at the corner: 0.707 is flat, higher values peak. On a shelf, 0.707 is the steepest slope without overshoot; higher values add a bump at the corner.

Output (output)#

A trim in dB after every band, so a boost does not push the next node into clipping.

Tips#

• Cut before you boost: a narrow cut is usually cleaner than a wide boost.
• Sweep a narrow bell with a high gain to find a ringing frequency, then flip the gain to cut it. Holding Alt while you drag solos the band, so you hear only the region you are sweeping.
• A low cut around 30 to 80 Hz removes rumble you cannot hear but a speaker still has to play.
• Use Output to match the level with the EQ on and off, so you judge the tone and not the loudness.

See also#

Filter, Low-pass filter, Compressor, Oscillator.

Help patches

Each help patch is an ordinary Toy that teaches one idea. The diagram shows the Patch; the preview shows its Frame. Open it in TuneToys to play and edit it.

1. Shape a tone with bells and shelves

beginner Teaches: band.gain, band.freq, band.gain, band.q, band.gain, output

A saw wave through the parametric EQ: shelves tilt the ends, a bell boosts or cuts the middle.

Connections as text

• Oscillator audio output connected to Parametric EQ audio input
• Parametric EQ audio output connected to Patch outputs audio input

• Open the EQ node: each band is a point on its screen. Drag the middle bell across and up or down.
• Mid Q narrows the bell. Shelves lift or lower everything below 120 Hz or above 6 kHz.
• Output trims the level after every band, so a big boost does not clip.

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2. Cut, notch and resonate

intermediate Teaches: band.enabled, band.freq, band.q, band.type, band.freq, band.enabled, band.freq

Low and high cuts frame a saw wave while a notch removes one band of harmonics.

Connections as text

• Oscillator audio output connected to Parametric EQ audio input
• Parametric EQ audio output connected to Patch outputs audio input

• Low cut removes everything under its frequency at 12 dB per octave. A high Q adds a resonant peak at the corner.
• Band 4 is a narrow notch on the 12th harmonic (1320 Hz). Switch its type to hear the other shapes.
• High cut softens the top. Turn either cut off to bypass it exactly.

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Related nodes

• Filter Low-pass, high-pass, band-pass, notch, all-pass or morphing filter with resonance, 12/24 dB slopes, curve editing and output RTA.
• Low-pass filter A gentle one-pole filter for warmer edges.
• Compressor Peak/RMS compression with a sidechain key input, detector filtering, hold, adaptive release and channel linking.
• Oscillator Selected waveform kernels, continuous morphing, harmonic shapes and phase/gate control; an optional MIDI input plays notes in the Toy's tuning.