Manual

How to use ZL Equalizer

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About

ZL Equalizer is an equalizer plugin with the following key features:

  • Multiple Filter Settings: Supports 6 filter structures, 16 frequency bands, 8 filter types, 5 stereo modes, 7 variable slopes.
  • High-Quality Sound: With 64-bit floating-point processing and de-cramping technique, outstanding performance is ensured in both low-end and high-end.
  • Adjustable Dynamics: Adjustable threshold, attack, release, and side-chain frequency, etc.
  • Carefully Designed Interface: Interactive spectrum graph, smart collision detection, and smooth animations.

User Interface

The user interface consists of a top panel, a main panel, and a bottom panel.

Components

Button

Click the button to switch between the “pressed” and “released” states.

Rotary/Horizontal/Vertical Slider

Values can be adjusted by dragging/clicking with the mouse or scrolling the mouse wheel. You can change the way of dragging.

Top Panel

General Setting

You can open the general setting panel by clicking General and close it by clicking somewhere else.

The components of this setting panel are:

Filter Structure

Zero Latency (Zero LAT)

  • OFF: turn off zero latency
  • ON: turn on zero latency
  • You can also click on the label on the left to switch options

When zero latency is on (and lookahead is zero), the plugin latency is zero. However, the buffer size will slightly affect dynamic effects and parameter automation.

Default Dynamic Link (Dyn Link)

  • OFF: turn off the default dynamic link (for bands of which the dynamic is enabled afterward, the dynamic link will be turned off by default)
  • ON: turn on the default dynamic link (for bands of which the dynamic is enabled afterward, the dynamic link will be turned on by default)
  • You can also click on the label on the left to switch options

When the dynamic link for a band is on, adjusting the frequency or Q value of the main filter will correspondingly adjust the frequency or Q value of the side-chain band-pass filter. You can control the dynamic link of each band using the dynamic link button.

Collision Detection Setting

You can open the collision detection setting panel by clicking Collision and close it by clicking somewhere else.

The components of this setting panel are:

Switch (DET)

  • OFF: turn off the collision detection
  • ON: turn on the collision detection
  • You can also click on the label on the left to switch options

Detection (Strength)

  • If you increase this parameter, the detected areas will become larger and darker

Detection (Scale)

  • If you increase this parameter, the detected areas will become darker

Collision detection compares the main-chain signal and the side-chain signal in real-time.

Generally, it should only be used when the plugin uses an external side-chain signal. When the plugin uses the internal side-chain, collision areas can be perceived as the spectrum peaks of the main-chain signal.

Collision detection uses an independent spectrum graph, which is not affected by Analyzer settings.

When collision detection is activated, the frame rate of the Main Panel will decrease to reduce the rendering pressure.

Collision detection may cause interface lag.

Output Setting

You can open the output detection setting panel by clicking Output and close it by clicking somewhere else.

When Gain Tag Colour is not fully transparent, the summation of SGC, AGC and Output Gain will show up per 1.5 second.

The components of this setting panel are:

  • Press: bypass the plugin
  • Release: turn on the plugin

  • Press: flip the phase of the output signal
  • Release: don’t flip the phase

Scale

The ratio of the actual gain over the displayed gain of all ‘gain type’ filters (Peak, Low Shelf, High Shelf, and Tilt Shelf) (including all base filters and target filters).

Static Gain Compensation（S）

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

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

Auto Gain Compensation (A)

  • 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.

AGC does not have effect under Linear Phase.

Output Gain

Dynamic Setting

You can open the dynamic detection setting panel by clicking Dynamic and close it by clicking somewhere else.

The components of this setting panel are:

Lookahead

  • the delay of the main-chain signal
  • when PDC is supported (hopefully in your DAW), it can be interpreted as the lookahead time of the side-chain signal

RMS

  • the length of the audio when calculating the instantaneous loudness
  • the actual attack/release will increase (significantly) when RMS increases

Smooth

  • the smoothness of attack/release

High Quality (HQ)

  • OFF: turn off the high-quality
  • ON: turn on the high-quality
  • You can also click on the label on the left to switch options

When high-quality is on, dynamic will adjust the filter state per sample, which smooths dynamic effects and reduces artifacts. However, high-quality will significantly increase the processing time of dynamic.

Analyzer Setting

You can open the analyzer setting panel by clicking Analyzer and close it by clicking somewhere else.

The components of this setting panel are:

FFT Mode

  • Pre, Post, and Side represents the input main-chain signal, the output main-chain signal, and the side-chain signal
  • OFF: turn off the spectrum
  • ON: turn on the spectrum
  • FRZ: freeze the spectrum
  • You can also click on the label on the left to switch options

Decay Speed

  • applies to spectrums that is on (and not frozen)

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

UI setting

Under custom colour mode, You can open the UI setting panel by clicking UI.

Bottom Panel

The bottom panel controls the parameters of the currently selected frequency band. Components will be introduced in the order from left to right, and from top to bottom.

Left Panel

  • Press: turn on the selected band.
  • Release: bypass the selected band.

  • Press: solo the audio affected by the selected frequency band.
  • Release: stop the solo.

Filter Type

There are a total of eight filter types: Peak, Low Shelf, Low Pass, High Shelf, High Pass, Notch, Band Pass, and Tilt Shelf.

Slope

There are seven slopes: 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

There are five stereo modes: Stereo, Left, Right, Mid, and Side.

Frequency (Freq)

Gain

When the dynamic feature is enabled, you can adjust the gain of the base filter by dragging/clicking with the left mouse button. To adjust the gain of the target filter, use the right mouse button for dragging/clicking. To adjust the gain of the base filter and the target filter, use the mousewheel.

Bandwidth (Q)

When the dynamic feature is enabled, you can adjust the Q value of the base filter by dragging/clicking with the left mouse button. For adjusting the Q value of the target filter, use the right mouse button for dragging/clicking. To adjust the Q values of the base filter and the target filter, use the mouse-wheel.

Band Selection

You can select the band by using the left arrows and right arrows.

  • Press: turn on the dynamic effect for the selected frequency band.
  • Release: turn off the dynamic effect for the selected frequency band.

  • Click: turns off the selected frequency band and resets all parameters to default values.

Right Panel

  • Press: cancel the bypass.
  • Release: bypass the dynamic effect for the selected frequency band.

  • Press: solo the side-chain audio of the selected band.
  • Release: stop the solo.

  • Press: set the dynamic threshold to the relative mode.
  • Release: set the dynamic threshold to the absolute mode.

  • Press: use external side-chain (this setting applies to all frequency bands).
  • Release: use internal side-chain (this setting applies to all frequency bands).

Threshold

Knee Width (Knee)

The adjusted knee width value is within the range of 0 to 1, and the actual knee width is this value multiplied by 60 dB.

Attack

Release

Side-chain Bandpass Frequency (Freq)

Adjust the center frequency of the bandpass filter applied to the side-chain audio. When the dynamic effect is turned on, this frequency will be automatically adjusted to fit the audio affected by the main-chain filter.

Side-chain Bandpass Bandwidth (Q)

Adjust the Q value of the bandpass filter applied to the side-chain audio. When the dynamic effect is turned on, this Q value will be automatically adjusted to fit the audio affected by the main-chain filter.

Main Panel

The main panel consists of grid lines, a spectrum graph, a single frequency band response curve, an overall response curve, and a dB scale on the right side.

Double-Click to Add a Frequency Band

If there is at least one frequency band in the off state when you double-click the spectrum, a frequency band will be turned on with the corresponding frequency/gain:

  • Frequency < 20Hz: Adds a High Pass filter.
  • 20Hz <= Frequency < 50Hz: Adds a Low Shelf filter.
  • 50Hz <= Frequency < 5000Hz: Adds a Peak filter.
  • 5000Hz <= Frequency < 15000Hz: Adds a High Shelf filter.
  • 15000Hz <= Frequency: Adds a Low Pass filter.

Frequency Band Drag Button

When a frequency band is not in the off state, a draggable button appears at the corresponding frequency/gain position. You can adjust the frequency and gain by dragging the button, and adjust the Q value with your mouse wheel.

When you select the frequency band, the button will be highlighted, and an additional control window will appear. Through this window, you can quickly bypass/solo the selected band and adjust the filter type.

Additionally, if the dynamic function of this frequency band is not disabled:

  • A draggable diamond-shaped button will appear at the corresponding position of the target filter, allowing you to adjust the frequency and gain of the target filter by dragging this button. After selecting it, you can adjust the Q value of the target filter by scrolling the mouse wheel.
  • A draggable square-shaped button will appear at the corresponding position of the side-chain bandpass filter, enabling you to adjust the frequency of the bandpass filter by dragging this button. After selecting it, you can adjust the Q value of the bandpass filter by scrolling the mouse wheel.
  • A dynamic link button will appear above the side-chain band-pass filter. You can enable/disable the dynamic link of that band by clicking this button.

When Filter Parameter Tags Colour is not fully transparent, the filter frequency/gain will appear as two tags on the spectrum.

Multi-band Selection

You can use your mouse to drag and select multiple frequency bands simultaneously on the spectrum graph. After that, you can click on the spectrum graph (outside the button area) to cancel the selection.

When multiple frequency bands are selected, bypassing/truning off one frequency band or adjusting the frequency/gain/bandwidth of one frequency band will also affect the corresponding parameters of the other selected frequency bands.

Decibel Scale

You can choose the maximum decibel for the decibel scale. After that, the maximum gain of filters (when you drag buttons) is limited to that range.

UI Setting Panel

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

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

Text Colour

Background Colour

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

Shadow Colour

Glow Colour

Main-Chain Input Signal Spectrum Colour (Pre Colour)

Main-Chain Output Signal Spectrum Colour (Post Colour)

Side-Chain Signal Spectrum Colour (Side Colour)

Grid Lines Colour (Grid Colour)

Filter Parameter Tags Colour (Tag Colour)

Gain Tag Colour (Gain Colour)

The following settings apply to all three colour modes:

Mouse-Wheel Sensitivity

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

Mouse-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.

Refresh Rate

  • The refresh rate of the response curve(s). The higher this value, the smoother the response curve(s) when dragging the buttons or enabling dynamic, but the higher the CPU and GPU load. When the CPU or GPU load is too high, the response curve may get distorted when dragging the button.

FFT Setting

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

Curve Thickness

  • Single: the thickness of the response curves of single bands
  • Sum: the thickness of the overall response curves

  • Save the current setting.

  • Load the default settings of some colours.

  • Discard all unsaved settings and close the UI setting panel.

Shortcuts

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

  • when using the mouse to drag / the mouse-wheel to adjust sliders, you can enable fine-adjustment with Shift
  • when dragging the band button, you can enable fine-dragging with Shift
  • when dragging the band button, you can fix frequency with Ctrl/Command + left-click and fix gain with Ctrl/Command + right-click
  • you can add a dynamic band by double-clicking with Ctrl/Command
  • you can turn on/off dynamic of a band by double-clicking with Ctrl/Command on the band button

Automation

You can automate frequency, gain, Q value, dynamic threshold, knee width, attack, and release parameters. Attention:

The modulation speed of automation is not less than 1000 times per second, but much slower than once per sample.

When the plugin window is open, filter parameter modulation may cause interface lag.

The plugin does not smooth modulation internally. Therefore, extremely fast modulation and modulation of other parameters may cause noise.

When you modulate multiple filters, DO NOT select them on the spectrum.

States of Bands

The frequency band can be in one of the following states:

  • Off: By default, all frequency bands are closed, not affecting the spectrum graph, the overall response curve, or the audio signal.
  • Bypassed: The response curve is displayed on the spectrum graph without affecting the overall response curve.
  • On: The response curve is displayed on the spectrum graph and affects both the overall response curve and the audio signal.

Dynamic and Automatic Threshold

The dynamic effect calculates the instantaneous loudness of the side-chain (filtered by the bandpass filter) at a constant rate (not less than 1000 times per second) and adjusts the filter state as follows:

  • When side-chain instantaneous loudness <= (threshold - knee width), the filter is in the base filter state.
  • When side-chain instantaneous loudness >= (threshold + knee width), the filter is in the target filter state.
  • When (threshold - knee width) < side-chain instantaneous loudness < (threshold + knee width), the filter parameters will be a mix of the baseline filter parameters and the target filter parameters with a proportion. And the filter state will be re-calculated. The closer the side-chain instantaneous loudness is to (threshold - knee width), the closer the filter state is to the baseline filter, and vice versa.

When automatic threshold is on, the plugin collects the side-chain’s instantaneous loudness and adjusts the threshold. The actual threshold is the automatic threshold + displayed threshold + 40.

When automatic threshold is turned off, the plugin sets the threshold to the median of the side-chain instantaneous loudness values and sets the knee width to half of the difference between the 95th and 5th percentiles.

When automatic threshold is off, the actual threshold is equal to the displayed threshold.

The threshold calculation is in the absolute mode by default. When the relative mode is activated, the dynamic effect will calculate the difference between the instantaneous loudness of the side-chain (filtered by the bandpass filter) and the overall instantaneous loudness of the side-chain. The threshold learning will work in the same mode.

Filter Structure

Minimum Phase

The most common filter structure of equalizers (Transposed-Direct-Form II). Low-order minimum phase filters (6 dB/oct and 12 dB/oct) cause small phase shifts. Therefore, when the signal processed by low-order minimum phase filters is mixed with the original or highly correlated signals, phase cancellation issues are almost inaudible. However, when frequency and gain are rapidly modulated, this type of filter is more likely to become unstable and produce audible artifacts.

State Variable

The most common filter structure of crossovers. This type of filter is more stable when frequency and gain are rapidly modulated. However, the phase shift caused by this type of filter is significant. It is not recommended to mix the processed signal with the original or highly correlated signals. What’s more, this type of filter will also affect the phase when it is bypassed.

Parallel

Under this filter structure, the Low Shelf (maximum 12 dB/oct) / High Sehlf (maximum 12 dB/oct) / Peak (maximum 24 dB/oct) filters are processed in Parallel while the remaining filters are still in Minimum Phase. For those parallel filters, the frequency response is DIFFERENT from the displayed curves. Besides that, Parallel filters perform dynamic processing in a different way, which is more efficient than Minimum Phase filters (especially under High Quality).

Matched Phase

All filters are still in Minimum Phase. Additionally, it uses a short FIR filter to match the magnitude/phase response of analog prototypes. This short FIR filter causes about 21 ms latency (up to about 64 ms if left/right or mid/side are used). I would advise against modulating parameters of filters with this structure.

Mixed Phase

All filters are still in Minimum Phase. Additionally, it uses a short FIR filter to match the magnitude response of analog prototypes and reduces phase shift at high-end. This short FIR filter causes about 43 ms latency (up to about 130 ms if left/right or mid/side are used). I would strongly advise against modulating parameters of filters with this structure.

Linear Phase

It has analog prototype magnitude response and zero phase response. This FIR filter causes about 171 ms latency (up to about 512 ms if left/right or mid/side are used). You should NOT modulate parameters of filters. Dynamic effect does not work.