Foreword
The stereo field has been central to audio production since the earliest days of multi-channel recording. When Alan Blumlein first demonstrated his stereophonic recording system in the 1930s, he revealed a new dimension in sound reproduction – the ability to locate sound sources in space, to create width and depth, to craft an immersive listening experience. Yet this advance also introduced new challenges, particularly when that carefully crafted stereo image must translate to mono playback.
Mono compatibility is not a relic of the past. Radio broadcasts, mobile device speakers, club sound systems, voice assistants, automotive systems – all commonly sum stereo signals to mono. When poorly managed phase relationships and extreme panning decisions encounter this summation, the results can be devastating: elements disappearing entirely, dramatic frequency cancellations, a mix that loses its fundamental balance and impact.
Beyond mono playback, stereo correlation plays a critical role in vinyl cutting, where excessive stereo width can cause physical cutting problems and stylus tracking issues. The cutting lathe must translate lateral and vertical groove modulations, and when left and right channels contain vastly different information – particularly at low frequencies – the mechanical limits of the medium can be exceeded. Mastering engineers have long managed correlation to ensure reliable vinyl pressings that play back cleanly without distortion or skipping.
Traditional approaches to ensuring mono compatibility often involve compromises. Narrow the stereo image too much and you sacrifice the space and dimension that makes modern mixes engaging. Leave the image too wide and you risk phase cancellations that can hollow out critical elements when summed to mono. Mid/Side processing offers powerful control, but requires careful management to avoid creating new problems while solving existing ones.
The concept of stereo correlation provides a more sophisticated framework for understanding these relationships. Perfect correlation (1.0) indicates that left and right channels are identical – effectively mono. Zero correlation means the channels are completely independent, maximizing stereo width but also creating the most potential for phase issues. Negative correlation represents out-of-phase relationships that can cause severe cancellations in mono.
But correlation is not a single number – it varies across the frequency spectrum. A vocal might be perfectly centered (high correlation) while cymbals spread wide (lower correlation). Bass frequencies often benefit from tighter correlation to maintain power in mono, while high frequencies can afford more independence for a sense of air and space. Managing these frequency-dependent relationships is the key to achieving both an engaging stereo image and solid mono translation.
The goal is not to eliminate stereo width, nor to force everything into perfect mono compatibility at the expense of dimension. Rather, it’s to intelligently manage the stereo field – preserving width where it serves the music while controlling problematic panning and phase relationships that compromise mono translation. Whether working in Left/Right mode to reduce excessive panning differences or Mid/Side mode to control the side channel directly, both approaches improve stereo correlation by bringing the left and right channels into closer agreement where needed. This requires tools that understand the frequency-dependent nature of stereo imaging and can apply precise, musical control where needed.
The Concept
OD Ancora draws its name from the Latin word for ‘anchor’. It is a stereo image correction processor that intelligently manages stereo width and improves mono compatibility through frequency-dependent panning & width correction. Operating without fixed crossovers and utilizing minimum phase filtering, Ancora analyzes stereo content in real-time and applies precise, phase-coherent corrections based on three customizable curves: Depth, Timing, and Target.
The processor offers two complementary processing modes. In L/R mode, Ancora analyzes the panning difference between left and right channels, reducing excessive panning that exceeds the Target threshold. This brings overly wide elements closer to center while maintaining the overall stereo field character. In M/S mode, Ancora operates on Mid/Side components, measuring and controlling the relative level difference between Side and Mid signals. This enables active correlation control, allowing you to shape stereo correlation into a desired range while maintaining phase-coherent imaging.
Unlike static stereo width controls or simple correlation meters, Ancora provides dynamic, frequency-dependent processing that adapts to the music. The system operates completely independently of input levels, providing true “set & forget” functionality. Through its three curve controls, you can define exactly how much processing is applied (Depth), how quickly it responds (Timing), and what threshold triggers correction (Target) – all varying across the frequency spectrum to match your source material.
The processor features a 100% vector-based user interface that delivers pristine visuals at any size, ensuring optimal workflow regardless of screen resolution or scaling. The underlying algorithm has been refined through extensive critical listening, resulting in a tool that responds musically and naturally to any source material while maintaining transparent, phase-coherent processing.
Note: Ancora’s FFT-based meters are optimized for musical audio and may not match traditional test signals or external analyzers, as analyzer parameters like FFT size and windowing function differ from Ancora’s internal settings.
Ancora Controls
Depth
 | Sets how strongly Ancora reduces panning differences. Higher values result in more centered, mono-compatible processing with reduced stereo width. This main control is bidirectionally linked with the Depth curve – adjusting the slider updates all curve handles proportionally, while modifying individual curve handles updates the slider to reflect their average value. Hold Shift and drag to activate multiplicative scaling mode, preserving the relative proportions of curve points. Tip: Start with moderate settings (around 5) to achieve improved mono compatibility without collapsing the stereo image completely. |
Bands
 | Determines the resolution of the full-spectrum analysis engine. Higher values provide finer frequency resolution, allowing more detailed control over individual frequency regions throughout the complete spectral range. The 12-bands-per-octave setting provides a good starting point for diverse material. |
Timing
 | Adjusts how quickly Ancora responds to changes in the audio signal. Lower values result in faster response that catches transient panning changes. Higher values create slower, smoother processing that preserves natural stereo dynamics. Like the Depth control, this slider is bidirectionally linked with the Timing curve, allowing both broad adjustments and frequency-specific fine-tuning. Hold Shift and drag to activate multiplicative scaling mode, preserving the relative proportions of curve points. Tip: Match values to source material – faster settings work well for dynamic stereo effects and transient-rich material, while slower values suit more stable stereo images. |
Target
 | Sets the target threshold in dB. In L/R mode, panning differences below this threshold remain unchanged, preserving natural stereo width – only panning beyond this value is reduced by the Depth control. In M/S mode, this sets the threshold for Side-Mid difference. When Side content exceeds this threshold relative to Mid, it is reduced by the Depth amount. At full Depth, this acts as a frequency-dependent correlation limiter, constraining maximum stereo width per frequency while maintaining phase-coherent processing. The Target control features the same intelligent bidirectional linking with its corresponding curve. Hold Shift and drag to activate multiplicative scaling mode, preserving the relative proportions of curve points. Note: Lower values (closer to -90dB) allow more stereo width to remain, while higher values (closer to 0dB) preserve less width before correction begins. |
Active
 | Enables or disables the Ancora processor. When disabled, the signal passes through completely unprocessed, allowing for quick A/B comparisons. |
Width
 | Controls the stereo width by applying gain to the Side signal in dB. Negative values reduce stereo width (narrower), 0 dB keeps the original width, and positive values expand stereo width (wider). Works in both L/R and M/S modes by internally converting to Mid/Side, applying the gain, and converting back. |
Channel Processing
Ancora offers two complementary processing modes for different stereo correction scenarios.
L/R Mode
 | In this mode, Ancora operates on the Left and Right channels, analyzing the panning difference between them. When this difference exceeds the Target threshold, Ancora reduces it by the amount set with Depth, bringing excessively panned elements closer to center while maintaining the overall stereo field. This improves mono compatibility without collapsing the stereo image completely. Use Case: Ideal for correcting excessive panning on individual tracks or busses, taming overly wide stereo effects, or improving overall mix mono compatibility. |
M/S Mode
 | In this mode, Ancora processes in Mid/Side domain. It measures the relative level difference between Side and Mid signals (S-M in dB). When this difference exceeds the Target threshold, Ancora attenuates the excess Side content by the Depth amount. This allows active correlation control, shaping the stereo correlation into your desired range while maintaining phase-coherent imaging. Use Case: Perfect for mastering applications requiring precise correlation control, managing excessive stereo width in the side channel, or creating frequency-dependent stereo width limiting at full Depth settings. |
The Curve System
Ancora’s unique curve system provides intuitive visual control over frequency-dependent stereo correction. Each curve type can be selected using its corresponding button, and all curves are displayed and edited directly on the spectrum analyzer.
Handle Value
 | Shows and controls the value of the selected drag handle. This field displays the current value of the selected handle and allows direct numeric input. The displayed value automatically updates when you drag handles in the spectrum display and is bidirectionally linked to the master sliders when changed here. Note: Only visible when a single handle is selected. |
Handle Frequency
 | Shows and controls the frequency of the selected drag handle. This field displays the current frequency of the selected handle and allows direct numeric input. The displayed value automatically updates when you drag handles in the spectrum display. Note: Only visible when a single handle is selected. |
Depth Curve
 | Shapes how strongly each frequency region is corrected. Apply more correction to problematic frequency ranges (like overly wide cymbals) while maintaining natural width in others (like centered vocals). |
Timing Curve
 | Adjusts the response speed across the frequency spectrum. Set faster times for controlling dynamic stereo effects in the high frequencies while maintaining slower, more musical processing in the low end for stable bass imaging. |
Target Curve
 | Defines frequency-dependent correction thresholds. In L/R mode, this sets how much panning must remain untouched before correction is applied per frequency. In M/S mode, this sets the maximum allowed Side-Mid difference before correction is applied. Lower values allow more stereo width, while higher values preserve less width before correction begins. |
Curve Editing
The spectrum display serves as both a real-time analyzer and an interactive curve editor:
- Click and drag any handle to adjust its frequency and value
- Double-click to add new points at specific frequencies
- Double-click on a handle to remove it
- Left-click and drag to create a selection rectangle around multiple handles for grouped adjustments
- Hold Shift and drag vertically to lock the frequency
- Hold Ctrl and click to select or deselect multiple handles
Each curve maintains between 2 and 12 active points, automatically interpolating smooth transitions between them.
Bidirectional Link Priority System
The bidirectional connection between sliders and curves employs an intelligent priority system to prevent feedback loops and ensure smooth operation:
When you adjust the main slider (Depth, Timing, or Target), the corresponding curve handles update proportionally while maintaining their relative positions. Conversely, when you modify individual curve handles, the main slider automatically reflects the average of all active points.
This system uses a priority mechanism that gives precedence to the most recent user action. Whether adjusting via the plugin GUI or through DAW automation, Ancora ensures that intended changes are applied without conflicts or unwanted feedback. For automation purposes, it is recommended to use the main sliders (Depth, Timing, Target) rather than individual curve points. Hold Shift and drag to activate multiplicative scaling mode, preserving the relative proportions of curve points.
The video below demonstrates the difference between additive and multiplicative scaling mode:
Note: If you would like to automate individual curve points, make sure you’re not automating them together with the corresponding main slider. The result is a seamless workflow where both detailed curve editing and quick overall adjustments feel natural and responsive.
Adaptive Load
Adaptive Load is a mechanism that constantly monitors the audio signal and corresponding states (such as filter memory) and frees up resources whenever possible – without any impact on processing quality. When Ancora is inserted on a track where audio only plays during certain parts of the song, the adaptive load mechanism detects silence and bypasses all of Ancora’s filters and processing, resulting in almost 0% CPU usage. This typically happens within several milliseconds. As soon as audio resumes, Ancora re-enables its processing. The entire process is fully transparent without any drawbacks. With Adaptive Load, resources are freed when not needed, which means you can use more plugins in your project and/or you will have lower export rendering times.
Toolbar
Undo/Redo
 | Use the undo/redo buttons to recall previous/next parameter changes. The exact event is shown in a tool tip. Please note that certain parameter changes are not tracked by this function (e.g. “Bypass”). |
Preset Management
The preset drop-down list offers quick access to factory settings and user presets.
 | The next/previous buttons allow you to cycle through the presets. |
Advanced preset management options are available from the context menu (Right-click).
Reset to Original state resets the currently active preset to its original state.
Save As New Global User Preset opens a dialog used to create User Presets. Note that these presets persist across sessions and DAWs (presets are saved on your machine). The total amount of user presets is limited to 20.
Overwrite/Rename Selected User-Preset allows to overwrite or rename presets.
Delete Selected User Preset allows to delete the current user preset.
Save As Default State replaces the plugins’ default preset with the current parameter state.
Revert Default State To Factory Setting deletes an overwritten default state.
Copy State (Ctrl+C) copies the current control states to the clipboard. This allows for applying control states (i.e. “presets”) across plugin instances and plugin hosts by using the Paste State command.
Paste State (Ctrl+V) pastes the control states from the clipboard.
Share State opens a dialog with additional preset sharing options via e-mail or internet forums.
A/B Control
 | A/B allows to compare two alternative parameter states. |
 | A>B and B<A copies one state to the other. |
Help
 | The dynamic help mode offers detailed information about the various elements of the user interface. Click “?” to activate the online help and move the mouse cursor over the control of interest. A small info bubble will appear displaying the function and details of the item. |
Delta Mode
 | Toggles Delta Mode on or off. When active, outputs only the difference between the original and processed signals, letting you hear exactly what Ancora adds or removes from your audio. Note: Delta Mode does not include the effects of the Width control. |
Theme
 | Opens the color theme selector. Choose from different visual themes to customize the plugin’s appearance. Each theme offers a unique color scheme for interface elements and curves. The selected theme is automatically synchronized across all open instances of the plugin and saved with your preferences. |
Settings
 | The settings button opens a dialog which gives control over additional plugin options. |
Slider allows for changing the behavior of knobs and control points in response to the mouse. Under Continuous Drag, knob and controller movement relies on mouse speed when Velocity is enabled. When Linear is enabled, knob and controller movement is proportional to mouse movement. Drag Sensitivity sets the linear sensitivity of the knob and controller movement further.
Plug-in controls, knobs, and control points can be adjusted using Left-click & drag (Continuous) and Right-click & drag (Stepped) by default. Mouse Configuration swaps the Continuous and Stepped behaviors between the left and right mouse buttons when selecting Invert Left/Right Buttons. Note that the default stepped values can be customized via the product configuration file. See “Local data” below for instructions on how to access this file.
Graphics allows for changing the interface size to a fixed percentage value between 100%, 125% and 150%.
Processing shows the plug-in latency and sample rate details. Highest quality rendering enables the option to always render at the highest Processing Quality, no matter what type is enabled in the Toolbar. See the “Processing Quality” subchapter for more details on these modes.
Registration offers access to offline and online product registration options. See the “Product Registration” chapter for more information.
Local Data allows for exporting and importing user preferences, presets, and keys, to and from other systems. Local data can also be deleted for all Tokyo Dawn Labs plug-ins using the Trash button.
In addition, the Folder button opens the Tokyo Dawn Labs local data folder containing all configuration files and keys. Note that these operations affect all TDR plug-ins, and not just Ancora
Updates allows to Check for updates and to Download latest version. Automatic Lookups can be enabled to Check for updates (once per day).
Help contains Documentation and Support links.
About shows the version number, build date, format, credits, and other information.
Context Menu
Standard Context Menu
Additional options can be accessed using the standard context menu. This can be opened by Right-clicking on a blank area anywhere in the UI. A click outside of the menu closes it.
User Interface Scale sets the on-screen interface size to a fixed percentage value of 100%, 125%, or 150%.
Instance allows for renaming the specific plug-in instance.
Copy State (Ctrl+C) copies the current control states to the clipboard. This allows for applying control states (i.e. “presets”) across plugin instances and plugin hosts by using the Paste State command.
Paste State (Ctrl+V) pastes the control states from the clipboard.
Share State opens a dialog with additional preset sharing options via e-mail or internet forums.
Adjusting Plugin Controls
Resetting Controls to Default Preset Values
Any control can be reset to its default preset position and value. This default position is the value that is set in the Default preset.
 | To reset a rotary control:
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Modifying Controls Using Text Entry
Many of the displayed control values have text boxes that can be modified directly.
 | To modify control values using text entry:
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Copyright and Acknowledgements
OD Ancora was conceived and developed by Jan Ohlhorst.
Documentation by Shane Johnson.
Software evaluation by:
Ady Connor
Aleksi Vuolevi
Andrew Boult
Audiobomber | Castlemastering
Bob Olhsson
Cyril Meysson
Dan Suter | echochamber
Dan Worrall
Dax Liniere | Puzzle Factory
Dean
Dennis J Wilkins | Studio 12 Below
Diogo C. Borges
Eric Recourt
EvilDragon
Greg Reierson
Gregg Janman | Hermetech Mastering
Helmut Erler | mastering.heyrec.org
Ilya Orlov
Janne Hatula
Jean Dante
Jeffrey Rippe
Jerry Anthony Mateo
Joe Caithness Mastering
Joseph Lyons
Justin Perkins
Laurent Sevestre
Michael Wynne
Miro Pajic
Murray Campbell | Beatworld
Niklas Silen
Nil Hartman
Pete Grandison
Resoundsound Mastering
Rich Prewett
Richard Pentrose
Robi Bulesic
Roland Löhlbach
Ruairi O’Flaherty
Sean Diggins
Sergey Makeev
Thaddeus Moore | Liquid Mastering
Titanio Studios
Valentin Zvukofor
Vitaly Zolotarev
© 2026 Ohlhorst Digital / Tokyo Dawn Records. All rights reserved.
All other product and company names are trademarks or registered trademarks of their respective holders.