Manual

How to use ZL Equalizer 2

About

ZL Equalizer 2 is a dynamic equalizer plugin with the following key features:

Unmatched Versatility: Sculpt your sound with 6 filter structures, 8 filter types, 5 stereo modes, 7 variable slopes, and up to 24 frequency bands.
Integrated Dynamic Control: Go beyond static EQ with adjustable threshold, attack, release, and side-chain filters for powerful dynamic equalization.
Pristine Precision: 64-bit floating-point processing and advanced de-cramping technique deliver outstanding performance, ensuring exceptional clarity from the deepest lows to the highest highs.
Intuitive Workflow: A carefully designed interface with an interactive spectrum graph, smart collision detection, and smooth animations makes equalization fast and fluid.

Top Panel

You can open the UI Setting Panel by double-clicking the logo.

Analyzer

You can open the Analyzer Setting Panel by clicking the text.

You can open the EQ Match Panel by clicking the icon.

Filter Structure

Minimum Phase: Minimum Phase
State Variable: State Variable
Parallel: Parallel
Matched Phase: Matched Phase
Mixed Phase: Mixed Phase
Zero Phase: Zero Phase

Output Panel

You can open the Output Setting Panel by clicking the text. It shows the current filter gain scale & total output gain.

Press: use the external side-chain
Release: use the internal side-chain

Release: bypass the plugin

Center Panel

The center panel consists of a spectrum analyzer, filter response curves, filter buttons, a floating window, and a decibel scale.

Spectrum Analyzer

The spectrum analyzer shows the spectrum of the input/output/side-chain signal and collision areas (optional). You can control it via the Analyzer Setting Panel.

Filter Response Curves

The filter response curves show the magnitude response of each single band and the magnitude response of each stereo placement.

Filter Buttons

The filter buttons are attached to filter response curves. You can drag them to change filter parameters. See more info in UI Controls.

When you double-click (with/without Ctrl/Command down) on the spectrum, a band will be added at the corresponding position (with/without dynamic behavior enabled) with a filter button.

Floating Window

The floating window is attached to the filter button of the selected band. You can control some filter parameters through this window.

Icon	Filter Type	Icon	Stereo Placement
	`Peak`		`Stereo`
	`Low Shelf`		`Left`
	`Low Pass`		`Right`
	`High Shelf`		`Mid`
	`High Pass`		`Side`
	`Notch`
	`Band Pass`
	`Tilt Shelf`

Right-click Panel

Invert Gain

Click: invert gain of the selected band

Split L/R

Click: set selected band to Left and add a band with same parameters but in Right

Split M/S

Click: set selected band to Mid and add a band with same parameters but in Side

Copy

Click: copy all selected bands’ filter parameters to the clipboard

Paste

Click: get filter parameters from the clipboard and create those bands

Decibel Scale

You can choose the decibel scale of magnitude response curves (through a combobox at the top-right) and the decibel scale of the spectrum analyzer (through a combobox at the bottom-right).

Bottom Panel

Left Panel

Release: bypass the band.

Band Selection

Select the current band.

Filter Type

Choose the filter type: Peak, Low Shelf, Low Pass, High Shelf, High Pass, Notch, Band Pass, and Tilt Shelf.

Slope

Choose the filter slope: 6 dB/oct, 12 dB/oct, 24 dB/oct, 36 dB/oct, 48 dB/oct, 72 dB/oct, and 96 dB/oct. A higher slope will make the filter’s response curve change more steeply. Peak, Notch, and Band Pass don’t support 6 dB/oct.

Stereo Modes

Choose the stereo mode: Stereo, Left, Right, Mid, and Side.

FREQ

Control the frequency. The maximum value of the frequency is affected by the sample rate.

GAIN

Control the base gain and the target gain. See more info in Dynamic Filter.

Q

Control the quality factor.

Press: turn on the dynamic behavior of the band

Click: turn off the band

Right Panel

Release: bypass the dynamic behavior. See more info in Dynamic Filter.

Press: turn on the dynamic learning behavior. See more info in Dynamic Filter.
Release: turn off the dynamic learning behavior and set the Threshold and Knee

Press: turn on the dynamic relative behavior. See more info in Dynamic Filter.

Press: change the side-chain stereo mode. When pressed, if the band is in Left/Right/Mid/Side, the side-chain band will be in Right/Left/Side/Mid.

Threshold

See more info in Dynamic Filter.

Knee

See more info in Dynamic Filter.

Attack

See more info in Dynamic Filter.

Release

See more info in Dynamic Filter.

Press: link the band with the side-chain band. See more info in Dynamic Filter.

Side-chain Filter Type

Choose the side-chain filter type: BP (Band Pass), LP (Low Pass), and HP (High Pass).

Side-chain Filter Slope

Choose the side-chain filter slope: 6 dB/oct, 12 dB/oct, 24 dB/oct, 36 dB/oct, 48 dB/oct, 72 dB/oct, and 96 dB/oct.

FREQ

Control the side-chain filter frequency.

Q

Control the side-chain filter quality factor.

Output Setting Panel

GAIN

Control the additional output gain.

SCALE

Control the scale of all filters’ base & target gain.

Press: turn on Static Gain Compensation
Release: turn off Static Gain Compensation

SGC estimates the amount of compensation from the filters’ parameters. SGC is inaccurate. However, it will NOT affect the dynamic of the main-chain signal.

Press: start to measure the integrated loudness of the input signal and the output signal
Release: turn AGC off and update the Output Gain to the difference between the two loudness values

Press: turn on Auto Gain Compensation
Release: turn off Auto Gain Compensation

AGC calculates the difference between the loudness of the main-chain signal before/after filters and applies the corresponding gain. Therefore, AGC will affect the dynamic of the main-chain signal.
When AGC is on, the output main-chain signal will pass through a hard clipper at 0 dB.

Press: flip the phase of the output signal

Lookahead

Control the lookahead of the side-chain signal.

Warning: Do not automate Lookahead.

Analyzer Setting Panel

Pre/Post/Side

Press: turn on the Pre/Post/Side analyzer
Release: turn off the Pre/Post/Side analyzer

Decay Speed

Slope

affects the spectrum display (not the actual signal)
0 dB/oct: no tilting, white noise displays as a horizon line
3 dB/oct: pink noise displays as a horizon line
4.5 dB/oct: default value, which represents perceived loudness better

Press: turn on the FFT freezing feature. When you hover the mouse over the analyzer for 2 seconds, the Post/Side analyzer will be frozen until you move the mouse.

Press: turn on the collision detection.

Strength

Control the collision detection strength.

EQ Match Panel

Warning: Once the EQ Match panel is open, DO NOT change the plugin’s sample rate (e.g., by changing the project sample rate or enabling DAW oversampling for this plugin). Otherwise, this plugin may crash the DAW.

EQ Match Steps

Open the EQ Match Panel. It will analyze the source signal and the target signal.
Choose the target signal. The source signal must be the main-chain input. You can choose the target signal from the side-chain input, a flat line, or a preset.
Wait till the difference curve becomes stable. Then adjust the difference curve with Shift, Smooth, and Slope. You can also draw the difference curve if you want.
Start the fitting. The fitting process should finish in several seconds. After that, you can adjust the number of bands.

EQ Match Analyzer

When the EQ Match Panel is visible, the analyzer displays three curves:

Source Curve: the average spectrum of the source signal.
Target Curve: the average spectrum of the target signal.
Difference Curve: the difference between the source signal and the target signal.

When the difference curve drawing is enabled, you can:

draw the difference curve with the left mouse button dragging
reset the difference curve with the right mouse button dragging
set the difference curve to zero with Shift + the left mouse button dragging
reset the whole difference curve with the left mouse button double-clicking

EQ Match Control

Click: save the target curve to a preset file

Press: enable the difference curve drawing

Target Signal

Choose the target signal:

Side: let the target curve be the average spectrum of the side-chain signal
Flat: set the target curve as a flat line
Preset: load the target curve from a preset file

Shift

Control the vertical shift of the difference curve.

Smooth

Control the smoothness of the difference curve.

from 0.0 to 0.5: the difference curve becomes smoother as the smoothness increases
from 0.5 to 1.0: the difference curve scales down as the smoothness increases

Slope

Control the (additional) slope of the difference curve.

Click: start the fitting process.

Warning: Once you click this button, ALL bands will be deleted and then be set to fitted parameters.

Number of Bands

Control the number of bands for fitting. You can control it after the fitting is completed.

UI Setting Panel

The UI setting panel controls analyzer colors, slider operations, etc. Components will be introduced in the order from top to bottom.

Color

You can adjust the color by clicking on the left color block and change the transparency by dragging the right slider.

Text Color

Background Color

For better accessibility, please set Text/Background to colors with high contrast.

Shadow Color

Glow Color

Pre Color

Post Color

Side Color

Collision Color

Grid Color

Color Map 1

The color map of the curves of each single filter.

Color Map 2

The color map of the curves of Stereo/Left/Right/Mid/Side.

Import Colors

Import color settings (.xml file)

Export Colors

Export color settings (.xml file)

Control

Wheel Sensitivity

Rough: mouse-wheel sensitivity when Shift is not pressed
Fine: mouse-wheel sensitivity when Shift is pressed
Reverse: whether to reverse the direction of mouse-wheel when Shift is pressed

Drag Sensitivity

Rough: mouse-drag sensitivity when Shift is not pressed
Fine: mouse-drag sensitivity when Shift is pressed

Rotary Slider Style

Circular: A rotary control that you move by dragging the mouse in a circular motion, like a knob
Horizontal: A rotary control that you move by dragging the mouse left-to-right
Vertical: A rotary control that you move by dragging the mouse up-and-down
Horiz + Vert: A rotary control that you move by dragging the mouse up-and-down or left-to-right
Distance: the relative distance that the mouse has to move to drag the slider across the full extent of its range. It does not apply to the Circular style.

Slider Double Click

Return Default: when you double-click the slider, it returns to the default value; when you double-click the slider with Ctrl/Command, it opens the value editor.
Open Editor: when you double-click the slider, it opens the value editor; when you double-click the slider with Ctrl/Command, it returns to the default value.

Import Controls

Import control settings (.xml file)

Export Controls

Export control settings (.xml file)

Other

Refresh Rate

In general, 30 Hz is enough for an equalizer plugin.

For a better analyzer display, set this to 1/n of your monitor refresh rate. For example,

If your monitor refresh rate is 120 Hz, set it to 120 Hz, 60 Hz (1/2), or 30 (1/4) Hz. DO NOT set it to 90 Hz.
If your monitor refresh rate is 90 Hz, set it to 90 Hz or 30 Hz (1/3). DO NOT set it to 60 Hz.

FFT Setting

Tilt: the extra tilting slope of the FFT
Speed: the extra decay speed of the FFT

Curve Thickness

Control the thickness of the curve of each band & each stereo mode.

Tooltip

Choose the tooltip language. It will take effect when the plugin window is reopened.

UI Scaling

Choose the font size mode.

Scale: the font size scales with the window size. Control the relative ratio.
Static: the font size is fixed. Control the actual font size.

UI Controls

Generally, you can enable fine-adjustment with Shift and enable special adjustment with Ctrl/Command. If the direction of the mouse wheel is reversed when Shift is pressed, you can reverse it again (in the UI Setting Panel) to put it back to normal.

Sliders

You can enable fine-adjustment with Shift when using the mouse to drag / the mouse wheel to adjust sliders.
You can use the left/right mouse button to control the first/second value when there are two values on the slider.

Filter Buttons

You can drag a button to change the frequency/gain value.
You can use the mouse wheel to change the Q value.
You can enable fine-adjustment with Shift when using the mouse to drag a button.
You can drag with the left mouse button + Ctrl/Command down while fixing the frequency.
You can drag with the right mouse button + Ctrl/Command down while fixing the frequency.
You can double-click the button to enter/exit the solo status.
You can double-click with Ctrl/Command to turn on/off the dynamic behavior.

Filter Structure

Minimum Phase

This is the standard, classic digital EQ sound. It’s the most common filter type.

Best For: General EQ tasks.
Pros: Gentle 6 dB and 12 dB/oct slopes cause very little phase shift, making it safe to blend with your original signal (low risk of cancellation).
Cons: Aggressive automation of frequency or gain can sometimes cause audible clicks or instability.

State Variable

This is the filter type often used in synth filters and crossovers.

Best For: Creative effects and heavy automation.
Pros: Extremely stable, even with rapid, complex automation.
Cons: Causes a significant phase shift. Avoid mixing this signal with the original (or other correlated signals) as it will likely cause phase cancellation.

Parallel

This mode changes how filters work together. Shelf (<= 12 dB/oct) and Peak (<= 24 dB/oct) filters are processed in parallel.

Best For: Efficient dynamic EQ processing & Natural sounding.
Pros: Offers a different character and is more CPU-efficient for dynamic tasks.
Cons: The parallel processing means the final EQ curve will look different from the curves shown on the display.

Matched Phase

This mode adds a special process to the Minimum Phase filters to mimic analog prototype magnitude & phase response.

Best For: Getting an analog phase and magnitude response.
Latency: Adds about 11 ms (up to 22 ms for L/R & M/S processing).
Cons: Dynamic filters stay in Minimum Phase.

Warning: Do not automate filter parameters in this mode.

Mixed Phase

This mode adds a special process to the Minimum Phase filters to mimic analog prototype magnitude response and clean up high-end phase.

Best For: Getting an analog magnitude response without the high-end phase shift (above 5 kHz).
Latency: Adds about 21 ms (up to 43 ms for L/R & M/S processing).
Cons: Dynamic filters stay in Minimum Phase.

Warning: Do not automate filter parameters in this mode.

Zero Phase

This mode provides almost zero phase response.

Best For: Surgical mastering tasks where preserving phase relationships is critical.
Pros: No phase distortion at all for mid/high frequencies (above 200 Hz).
Cons: Adds a very high latency of about 171 ms (up to 342 ms for L/R & M/S processing). May cause audible pre-ringing. Dynamic filters stay in Minimum Phase.

Warning: Do not automate filter parameters in this mode.

Dynamic Filter

How the Dynamic Filter Works

A dynamic filter automatically turns an EQ band up or down for you, but only when specific frequencies get too loud or too quiet.

Core Dynamic Behavior

When dynamic mode is enabled, the filter listens to a specific frequency range, i.e., the side-chain signal filtered by the side-chain filter. The settings tell it when to react and how fast.

Threshold: This is the trigger level.
- When the signal’s volume crosses above Threshold, the filter starts to change to the target gain. The reaction speed is controlled by Attack.
- When the signal’s volume falls below Threshold, the filter starts to change to the base gain. The reset speed is controlled by Release.
Knee: This controls how smoothly the filter reacts as the signal approaches the Threshold.
- A hard knee (low value) is like a switch: the filter stays at base gain until the signal exactly crosses the Threshold.
- A soft knee (high value) is like a dimmer: the filter gently moves to target gain as the signal gets close to the Threshold, resulting in a more gradual and transparent effect.

Please do keep in mind that the definition of Threshold and Knee is different from traditional compressors.

Dynamic Learning

Setting the Threshold and Knee perfectly can be tricky, especially if the track’s volume changes.

When you enable Dynamic Learning, the plugin does the work for you. It continuously analyzes the incoming signal and automatically sets the Threshold and Knee in real-time. This keeps the dynamic processing adapted to the signal.

Dynamic Relative

This mode completely changes what the filter listens to.

Normal Mode is triggered by the absolute volume: Is the filtered side-chain loud in absolute terms?
Relative Mode is triggered by the relative volume: Is the filtered side-chain louder than the whole side-chain?