ZEROLINE is a gain staging utility that measures each track’s average level before mixing and locks the trim value in a single action. Available as the free edition ZEROLINE and the upgraded edition ZEROLINE Pro with added features. This manual covers both editions. Features exclusive to the Pro edition are marked as “Pro only”.

Free vs Pro

Feature	ZEROLINE (free)	ZEROLINE Pro
LEARN (measures average level and locks trim value)	✓	✓
TRIM knob, Ø (phase invert)	✓	✓
IN / OUT VU meters, CLIP indicator, PEAK WARNING	✓	✓
Target level	Fixed at 0 VU = -18 dBFS	Choose VU / LUFS / PEAK in TARGET
MATCH (matches levels before and after effects)	—	✓
LEARN ALL (measures all tracks simultaneously)	—	✓
Price / Availability	Free (Official website / Gumroad / itch.io)	¥500 (Gumroad) / $3.25 (itch.io)

In the free edition, the TARGET panel and MATCH panel have a “PRO” badge and cannot be adjusted.

1. Overview

Gain staging is an essential preparation step to align each track’s volume to a reference level suitable for mixing. ZEROLINE measures the average level simply by playing track audio and clicking a button, setting the optimal trim value in a single action.

• “No continuous following” — reliable locked trim: Once measured with the LEARN feature, the calculated trim value is completely locked (LOCKED). Because it does not continuously track and adjust volume, there is no risk of it unintentionally acting like a slow compressor.
• Flexible target references (TARGET, Pro only): In addition to industry-standard VU (average level) metering, it features Integrated LUFS loudness metering and a PEAK mode to align peaks. Gain stage to match your workflow or streaming standards.
• Pre/post-effect level matching (MATCH, Pro only): By placing an instance before and after a plugin chain, it measures and locks the trim to cancel out volume changes introduced by the effects. Switching the effects and the OUT instance together allows you to compare tonal changes without being misled by volume differences.
• Batch measurement across all project tracks (LEARN ALL, Pro only): A single button lets you perform LEARN on all ZEROLINE Pro instances across your project at once.
• Zero-latency design: Processing introduces zero latency.

2. Requirements

Item	Details
Supported OS	Windows 10 / 11 (64-bit), macOS 11 or later (Apple Silicon / Intel)
Plugin format	Windows: VST3 / Mac: VST3, AU
Supported hosts	VST3 or AU compatible DAWs
Input / output channels	Mono / Stereo
Sample rate	Host (DAW) dependent
Screen size	720 × 480 px (fixed, non-resizable)
Latency	None (0 samples)
Presets	None
Bypass	Please use the DAW host’s bypass feature

3. Installation

Installation (Windows)

1. Extract the downloaded ZIP file (contents: ZEROLINE.vst3 (or ZEROLINE Pro.vst3 for Pro), README.txt, manual HTML).
2. Copy the ZEROLINE.vst3 folder (or ZEROLINE Pro.vst3 for Pro) to the following location:
   C:\Program Files\Common Files\VST3\
3. Launch your DAW and run a plugin rescan (if you copy while the DAW is open, it may not detect the plugin).

Installation (Mac)

1. Extract the downloaded ZIP file.
2. Copy ZEROLINE.vst3 (or ZEROLINE Pro.vst3 for Pro) to ~/Library/Audio/Plug-Ins/VST3/, and copy ZEROLINE.component (or ZEROLINE Pro.component for Pro) to ~/Library/Audio/Plug-Ins/Components/ (~ represents your home folder. In Finder, open the “Go” menu, choose “Go to Folder…”, and paste the path. If the destination folder does not exist, create a new one).
3. Open Terminal (Applications → Utilities → Terminal), then copy and paste the following three lines one by one, pressing the Return key after each line:
   Free:

   cd ~/Library/Audio/Plug-Ins
   xattr -dr com.apple.quarantine VST3/"ZEROLINE.vst3"
   xattr -dr com.apple.quarantine Components/"ZEROLINE.component"

   Pro:

   cd ~/Library/Audio/Plug-Ins
   xattr -dr com.apple.quarantine VST3/"ZEROLINE Pro.vst3"
   xattr -dr com.apple.quarantine Components/"ZEROLINE Pro.component"

4. Launch your DAW and run a plugin rescan (if you copy while the DAW is open, it may not detect the plugin. If AU does not appear in Logic Pro or other DAWs, restart your Mac).

Uninstall

[Windows] Delete the copied ZEROLINE.vst3 folder (or ZEROLINE Pro.vst3 for Pro).
[Mac] Delete the copied ZEROLINE.vst3 and ZEROLINE.component files (or ZEROLINE Pro.vst3 and ZEROLINE Pro.component for Pro).

4. The screen

The screen size is fixed at 720 × 480 px. The role and layout of each panel are as follows:

• Header bar (top): Displays the brand logo and version number (v1.1.0) in the top-left corner. On the right side, when ROLE is IN or OUT, a role indicator such as “MATCH IN · A” is displayed (Pro only).
• InfoBar (upper bar): Located right below the header. Hovering the mouse cursor over knobs or buttons in each panel displays descriptions of their functions and how to use them, shown in English or Japanese, following the OS display language.
• LEVEL panel (left):
  • VU meters: Equipped with two meters: the IN meter displaying the input signal (pre-trim) and the OUT meter displaying the output signal (post-trim). The green line indicates the target value (0 VU).
  • CLIP indicator: Located at the top of the meters, it lights up in red for 2 seconds as a warning when the signal exceeds -0.2 dBFS.
  • Reference level readout: Displays the current reference setting at the bottom of the meters, such as “0 VU = -18 dBFS” (always -18 dBFS in the free edition).
• TRIM panel (center):
  • TRIM knob: A large knob for gain adjustment (-24.0 to +24.0 dB in 0.1 dB steps). Manual fine-tuning is supported.
  • LEARN button: Starts and stops automatic measurement of the average level.
  • Status display: A 2-line display showing the current operating status (line 1 shows English status, line 2 shows detailed information or measured values).
  • Ø button: Inverts the signal polarity (180-degree phase flip).
• TARGET panel (top-right, Pro only): Sets the target reference mode (MODE) and target level (LEVEL) for measurement. In the free edition, it displays a “PRO” badge and cannot be adjusted.
• MATCH panel (bottom-right, Pro only): A feature to match levels before and after effects. Contains role selection (ROLE: OFF / IN / OUT), group selection (GROUP: A–H), and the batch measurement LEARN ALL button (switches to the MATCH button when ROLE is OUT). In the free edition, it displays a “PRO” badge and cannot be adjusted.

5. Using LEARN

LEARN is the primary feature that measures track volume and automatically determines the optimal trim value.

Measurement steps

1. Insert ZEROLINE at the beginning of the track’s effect chain (or immediately after the instrument on instrument tracks).
2. Start playback in your DAW.
3. Click the LEARN button (the status display changes to LEARNING).
4. Play the loudest, most representative section where the part is playing consistently (such as a chorus) for several seconds.
5. Click the LEARN button again, or stop DAW playback.
6. The trim value is determined and locked at that value (the status display shows LOCKED, and line 2 displays the measured input level; in the Pro edition, it is shown in the unit of the selected MODE. The resulting trim value can be viewed on the TRIM knob).

In the free edition, the target level is fixed at 0 VU = -18 dBFS (average level). In the Pro edition, it can be changed in the TARGET panel.

Measurement details and tips

• Measurement target: Measures the input signal before the trim. Manually turning the TRIM knob during LEARN measurement does not affect the measurement result. In addition, silent sections without playing are automatically excluded from measurement.
• Measurement duration: There is no upper limit on measurement time. Even a few seconds of measurement will determine a trim value, but extremely short measurements may lead to inconsistent results. Also, measuring only during quiet intros or breakdowns can cause the trim to boost excessively; measure during the loudest section instead.
• Session saving and fine-tuning: The determined trim value is saved in your DAW session file. You can also manually adjust the TRIM knob after measurement for fine-tuning.
• Peak handling and PEAK WARNING: This plugin aligns average levels and does not align peak levels. If aligning by average level is expected to result in an output peak near 0 dBFS (-0.2 dBFS or higher), PEAK WARNING is shown in the status display (while internal 32-bit floating-point processing in DAWs will not immediately clip above 0 dBFS, be mindful of excessive input into subsequent plugins or hardware).

6. TARGET (Pro only)

TARGET is a Pro-only panel that configures the target reference mode (MODE) and target volume (LEVEL) for measurement.

MODE (measurement mode)

• VU (default): Measures based on average level (VU). A green target line (0 VU) is displayed on the meter.
• LUFS: Measures based on perceived loudness (Integrated LUFS).
• PEAK: Measures based on sample peak. Determines the trim value so that peaks do not exceed the target level. PEAK WARNING does not occur when measuring in PEAK mode.

LEVEL (target level)

The adjustment range and default value for LEVEL are stored independently for each MODE.

• In VU mode: Sets the reference level defining what dBFS corresponds to 0 VU (-24.0 to -8.0 dBFS, default: -18.0 dBFS). Switch this to match your studio working standards (such as -20 dBFS, -18 dBFS, or -14 dBFS).
• In LUFS mode: Sets the target Integrated LUFS value (-36.0 to -10.0 LUFS, default: -18.0 LUFS).
• In PEAK mode: Sets the target peak dBFS value (-24.0 to 0.0 dBFS, default: -6.0 dBFS).

7. MATCH (Pro only)

MATCH is a Pro-only feature that accurately matches levels before and after effects such as compressors or saturators. It allows you to evaluate tonal changes without falling for the psychoacoustic illusion of “louder sounds better.”

Setup steps

1. Insert two ZEROLINE Pro instances on a single track.
   Layout: [ZEROLINE Pro (IN)] → [Target effects] → [ZEROLINE Pro (OUT)]
   On Mac DAWs that support both AU and VST3, insert both instances in the same format (both AU or both VST3).
2. Set GROUP on both instances to the same group (any letter from A to H).
3. Set ROLE on the instance before the effects to IN, and set ROLE on the instance after the effects to OUT.
4. Start playback in your DAW, and click the MATCH button located at the bottom of the MATCH panel on the OUT instance.
5. After playing a section where audio is consistently playing, click the MATCH button again, or stop DAW playback.
6. The trim value is automatically locked so that the OUT instance’s output level matches the IN instance’s output level (status display: LOCKED).

Color indicators by ROLE and how to identify them

To prevent configuration errors, the screen’s theme color changes according to ROLE.

• ROLE: IN (Blue): The header bar color, top-right display (“MATCH IN · A”), and ROLE button turn blue.
• ROLE: OUT (Orange): The header bar color, top-right display (“MATCH OUT · A”), ROLE button, and the meters on the LEVEL panel turn orange.

8. LEARN ALL (Pro only)

LEARN ALL is a feature that performs LEARN across all tracks where ZEROLINE Pro is inserted simultaneously (excluding instances where ROLE is set to OUT).

• Starting and stopping simultaneous measurement: Clicking the LEARN ALL button on any instance starts LEARN across all ZEROLINE Pro instances in the project (where ROLE is OFF or IN) at once. Clicking it again or stopping DAW playback finishes measurement and locks the trim value across all tracks simultaneously.
• Count readout: During LEARN ALL measurement, line 2 of the status display shows the number of instances being measured together and the elapsed time, such as ALL 6 / 3.2 s. If the count is lower than expected, some instances may have ROLE set to OUT or use different formats (AU vs. VST3 on Mac).
• Individual track completion: Clicking the individual LEARN button on a specific instance during LEARN ALL measurement finishes measurement for that track individually.
• Exclusion of ROLE: OUT: Instances with ROLE set to OUT are excluded from batch measurement and display SKIPPED in their status display. After LEARN ALL is complete, run MATCH individually on each OUT instance.
• Process setting limitation: As with MATCH, instances cannot communicate when running under DAW plugin sandboxing (separate process execution).
• Scope by plugin format: When mixing AU and VST3 formats on Mac, LEARN ALL only affects ZEROLINE Pro instances sharing the same format as the clicked instance.
• After LEARN ALL: Once all tracks are aligned to the same reference level, build your mix balance using your channel faders. LEARN ALL creates the foundation for your mix; it does not set the balance itself.

9. Status display

A list of status messages shown in the TRIM panel status display. Line 1 shows a color-coded status, and line 2 shows detailed information or measured values.

Standard LEARN status

• PLAY, THEN LEARN: Standing by. Start playback, then click the LEARN button.
• LEARNING: Measuring (line 2 shows elapsed time; during LEARN ALL, it also shows the count being measured together, such as ALL 6 / 3.2 s).
• LOCKED: Trim value locked (line 2 shows measured input level, e.g., -5.0 VU; in the Pro edition LUFS / PEAK modes, -23.0 LUFS / -20.0 dBFS).
• PEAK WARNING: Trim value locked, but the output peak is expected to be high (-0.2 dBFS or higher; line 2 shows estimated peak value).
• OUT OF RANGE: The trim value required to reach the target level exceeded the allowable range (±24.0 dB) and was clamped to the maximum or minimum limit (line 2 shows clamped value).
• NO SIGNAL: No measurable audio signal detected. Trim value was not changed (check plugin placement and track playback).

MATCH status (Pro only)

• PLAY, THEN MATCH: Standing by. Start playback, then click the MATCH button.
• LOCKED: Pre- and post-effect levels matched and trim value locked (line 2 displays the determined trim value, such as “MATCH +6.0 dB”).
• NO PARTNER: No corresponding IN instance exists in the same group (GROUP). Trim value was not changed.
• AMBIGUOUS: Two or more IN or OUT instances exist in the same group (GROUP), making it impossible to identify the pair. Trim value was not changed.

LEARN ALL status (Pro only)

• SKIPPED: Shown on instances where ROLE is set to OUT (indicates exclusion from batch measurement; line 2 shows OUT uses MATCH).

10. Tips

• Leveling the foundation of your mix:
  What ZEROLINE levels is the signal level before entering your effect chain. Because downstream compressors and saturators receive a consistent level every time, presets and settings become much easier to reuse. Since all tracks are brought to the same average level, a hi-hat and a lead vocal would sound equally loud if left as-is. Set the final volume balance between tracks using your channel faders afterward.
• Plugin placement:
  Insert at the beginning of each track’s effect chain (immediately after virtual instruments on instrument tracks). Aligning each track’s average volume in advance stabilizes input gain into subsequent compressors and saturators, making presets and settings much easier to reuse.
• Why it does not follow continuously:
  ZEROLINE is designed to lock the trim value once measured. If it tracked volume in real time, gain would rise in quiet passages and fall in loud sections, acting like an unwanted compressor and destroying dynamics.
• Choosing the measurement section:
  When measuring, play the section where the track plays most prominently (such as a chorus). Measuring only during quiet intros or gaps between phrases will cause the trim to boost excessively.
• Handling peak warnings (PEAK WARNING):
  ZEROLINE adjusts levels based on average level (VU), which closely matches human auditory perception, rather than peak values. Therefore, on transient-heavy sounds like snare drums or percussion, leveling to 0 VU may cause peaks to jump near 0 dBFS (-0.2 dBFS or higher). Because modern DAWs process audio in floating-point format, exceeding 0 dBFS internally will not immediately cause harsh digital clipping. However, subsequent gear or plugins may distort, so if this concerns you, simply lower the TRIM knob slightly by hand.
• Using the phase invert (Ø) button:
  When layering multiple microphones or lines—such as multi-mic drums (snare top/bottom, kick in/out) or bass line/amp recordings—pressing the Ø button to flip phase is convenient for checking low-end punch and body.
• About bypass:
  ZEROLINE does not include a dedicated BYPASS button on its interface. To compare sound by bypassing the plugin, use the bypass button in your DAW’s track insert slot.
• Comparing audio with MATCH (Pro only):
  Using MATCH before and after effects avoids the psychological pitfall where “louder sounds better.” When comparing, bypass the effects and the OUT ZEROLINE Pro instance at the same time.
• Checking DAW sandboxing settings (Pro only):
  If MATCH or LEARN ALL results in NO PARTNER, check whether plugin sandboxing (separate process execution) is enabled in your DAW settings, and configure it to run instances within the same process. On Mac, also verify that IN and OUT share the same format (both AU or both VST3).

11. Notes

ZEROLINE (free)

• This product is distributed free of charge (freeware) “AS IS”, without support. Feedback and suggestions are welcome at info@tonecraft.blue-x.tokyo. We cannot promise individual support.
• The source code is proprietary and not public.
• All copyrights to this product belong to Tonecraft Tokyo.
• Modification, reverse engineering, redistribution, and resale of this product are strictly prohibited (please download from the Tonecraft Tokyo official website and BOOTH).
• Free for both commercial and non-commercial use.

ZEROLINE Pro

• This product comes with no support and is provided as is. We cannot promise individual support. Feedback and comments are welcome at info@tonecraft.blue-x.tokyo.
• No refunds are provided.
• The source code is proprietary and not public.
• Copyright for this product belongs to Tonecraft Tokyo.
• Redistribution, resale, modification, and reverse engineering of this product are prohibited.
• Only the purchaser may use this product. Transferring or sharing it with third parties is prohibited.

12. Disclaimer

• This product is provided “AS IS”, without warranty of any kind, express or implied, including but not limited to merchantability, fitness for a particular purpose, and non-infringement of third-party rights.
• Tonecraft Tokyo is not liable for any damages arising from the use of, or inability to use, this product, including but not limited to loss or corruption of project files or audio data, equipment malfunction, lost working time, or lost profits.
• Operation is not guaranteed for every combination of DAW, operating system, and hardware.
• Specifications may change, and the product may be discontinued, without notice.
• Use this product at your own risk. Back up your projects before important work.

13. Licenses

• VST is a trademark of Steinberg Media Technologies GmbH.
• This product uses JUCE.
• Noto Sans JP / JetBrains Mono — SIL Open Font License 1.1