thEQred — Preeminent Linear Phase Equalizer

Linear phase precision, velvet softness



Frequency–domain linear phase as only MAAT can make it.

• thEQred Perpetual License: $489
• thEQlp Linear Phase Subscription: $119 Annual Renewal

[thEQred + thEQorange: $9.92 per month billed annually]
• All EQ Big Bundle: $1099, $557 Total Savings
[25% Off thEQblue12, thEQred, thEQorange + free SantaCruzEQ6]
thEQred Panorama Control

Red Is The New Black

Think of thEQred as LP PEQ Red 2.0…we’ve taken the fundamentals of Algorithmix’s exemplary LinearPhase PEQ Red, and given it a MAAT makeover. There is no other æsthetic equalizer like thEQred. With its ability to invisibly provide spectral counterweight to mixes that lean one way or another, thEQred excels at straightening up biased content. Add crystalline air without stridency to a dark mix, or beef up lower mids and bass without bloat or loss of focus. With twelve bands or Sections of precision, linear phase parametric equalization featuring unique shelving filters, mastery of complex mixes without changing their overall sonic character is just a few clicks away.

A little backstory…An idea was born to reissue this masterpiece, along with the other legendary Algorithmix EQs, and make it available as 64 bit in all common formats and (finally!) for macOS. As a power user, our visionary Friedemann had some ideas in mind regarding the improvements. Specifically, he wanted to make the user interface, the UI, more flexible and faster to use because there is no other tool in the mastering chain that receives as much “seat time.” The result: Our thEQ UI and feature set. The UI affords super fast setup and includes a number of unique features which help to speed your work: The positive & negative Contribution function including absolute difference, the highly adjustable sonogram which makes detecting problem spots easy, and the possibility to play a note on the keyboard that you have in your head and then snap a Section to that respective frequency with one click. Also, having all twelve Sections visible simultaneously, not to mention the SORT button function.

Frequency Forward

thEQred works in the frequency domain. That is, the input signal is first transformed into a spectral representation. Then, that spectral equivalent is operated upon. Special measures have been taken to ensure high resolution at critical low frequencies while keeping temporal resolution untouched. Unlike common frequency-domain filters, our linear phase approach avoids drums or other instrument containing strong transients from being blurred. In addition, extremely high compute resolution has been used to avoid any cumulative truncation effects typical in complex frequency transforms. This results in unblemished sound quality.
There are other plug–ins on the market using frequency–domain techniques. Most of them apply relatively low frequency resolution and then claim that frequency response mathematically interpolated between a few set points or that freehand drawing is the best solution. This may be true for some industrial applications, but such filters simply don’t sound musical. We’ve worked hard to insure that filter shapes in thEQred exactly match the best analog references. The result is sonic quality that is undisputed, even at baseband 44.1 and 48 kHz rates.

Unobtrusive Power

“An equalizer should have no, ideally, should have no distortion of its own. It’s almost impossible to do it without some distortion but, that’s the aim. So, if you can do that…Now there are a lot of equalizers about, where people have just taken a circuit out of some reference book and hoped for the best and they’ve never really succeeded because they haven’t taken into account all these other things.” — Rupert Neve on EQ in Rupert Neve: The SOS Interview on YouTube

thEQred was designed to deliver the highest possible linearity down to subsonic frequencies. This and other powerful features hide behind its clean and simple UI. Eye candy is great for newbies, but thEQr isn’t your typical filter: thEQred packs all the advanced features you need into one resizable window that’s easy on the eyes. Not only does the UI “get out of the way” so you can be more productive, we’ve incorporated industry–first features that speed your workflow, neatly packaged to make thEQred easy and intuitive to use.

thEQred Pennant
thEQred Topo Controls

Better By Design

Whether you’re looking for gentle rehabilitation, colorless correction, or simply baggage–free spectral contouring, our proprietary, precision algorithm delivers on the promise of linear phase EQ. Bring the power and purity of thEQred to bear for all your critical equalization tasks.

As Friedemann says, “It’s all about the curves.” Along with all the features of our thEQ family, thEQred incorporates a unique and proprietary filter technology allowing you to adjust any slope between nearly 0 and 24 dB/octave. Almost any filter needed or desired can be dialed in quickly and easily, from broad shallow strokes to cascaded deep cuts.


  • Five Panorama modes; stereo, mono (L+R), left–only, right–only and difference (L-R) for focused treatment or enhancement
  • Two Stereo modes; Left/Right or Mid/Side
  • Four Contribution modes; positive addition only, negative addition only, EQ contribution only, and “normal” EQ out help you to keep track of your progress
  • Extended frequency range covers the ultrasonic, suitable for any HRA post
  • Equal delay at all frequencies independent of filter settings, perfectly preserving the time relationship of harmonics
  • No phase distortion and no temporal dispersion, eliminating transient smear
  • Freedom from unwanted coloration for exceptional clarity, transparency, and definition
  • Exclusive VariSlope technology offers shelf and cut filters with any roll-off in the range of 6 to 24 dB/octave as well as continuous slope adjustment below 6 dB/octave, impossible with any classic filter
  • Twelve Sections with eight freely assignable parametric filter types: classic bell, high or low shelf, high or low cut as well as VariSlope high or low shelf, and high or low cut
  • Adjustable Q for shelving and cut filters
  • Proprietary algorithms deliver extraordinarily low distortion and noise
  • For ultimate fidelity, deep 80 bit super double precision internals virtually eliminate rounding errors and distortion
  • Perfect emulation of analog filter characteristics, clearly perceptible when equalizing audio at baseband sample rates
  • Extremely shallow VariSlope shelves for gentle brightening or added weight
  • Cascade cut filters for “brick wall” characteristics
  • Resizable UI for easy and precise adjustments or for ultra–high resolution displays
  • MAAT’s smart AutoGain for effortless A/B comparisons
  • Inbuilt tone generator makes for quick location of trouble spots
  • SORT function eliminates the need for busy, distracting UI elements
  • TUNE function aligns center frequencies to Western tunings
  • Grid snap toggles between surgical and musical applications, emulating popular hardware resonant frequency choices, including Maselec and Manley


  • Exclusive dual view, monochrome/color real time spectrogram with user adjustable temporal wiper lets you choose “when” to transition to low distraction monochrome
  • Choice of parametric editing via numerical fields or directly via the graphical display
  • Operates at up to 384 kHz sample rates for HRA or game audio workflows
  • Complete setup exchange across multiple instances
  • Automatic latency compensation with all modern DAWs
  • A/B comparison for fast decision making
thEQred is a unique tool for mastering engineers who already have access to diverse high end EQs for different tasks. There are several frequency–domain, linear phase EQs on the market, but thEQred, with its wide, 80 bit double precision processing and optimized–for–fidelity algorithm, will bring a new sense of transparency to your work.
With all the features and functionality of Algorithmix’s beloved original LP PEQ Red, the feature–packed thEQred brings so much more. Use its powerful processing and double precision I/O for:
  • Mastering and remastering tasks on complex, high fidelity mixes
  • Removing unwanted ultrasonic content from HRA recordings
  • Identifying resonances with ease when sweeping, due to the low inherent ringing
  • Putting mixes with too much DC or a super fat kick on a diet
  • Uncolored aesthetic equalization of acoustic performances, perfect for classical, jazz and folk
  • VariSlope rebalancing of unbalanced mixes
  • Adding super-clear and inconspicuous “air” to dark material
All true linear phase EQs have similar specs. Dirac spikes and other artificial test signals will produce about the same results regardless of whose product you try. A solo chime or kick drum track is not what thEQred was designed for. As for all our thEQ products, it excels at equalizing actual music!
What not to use thEQred for is tracking or mixing! thEQred is a low channel count plug–in, designed for the master buss and mastering. Due to the insane complexity of the algorithm, thEQred has a hefty CPU demand. It’s not a “light weight”!
thEQred fits in with all modern workflows:
  • Supports LPCM sample rates up to 384k for DSD and high–end postproduction
  • All standard formats: AU, VST 2 and 3, AAX
  • Compatible with macOS and Windows
  • Low fatigue visual design
  • Resizable user interface for every screen resolution

Linear Phase Royalty

Most all parametric equalizers or PEQs are implemented via phase shift. That is, the incoming dry signal is mixed with a phase–shifted version. Because the amount of the phase shift is frequency dependent, some cancellation or reinforcement occurs at the desired frequency. It gets the job done, but with a major disadvantage: the different signal components of the resulting audio become spread out in time, so time relationships between harmonics in the filtered output is heavily altered. The result: a nice sharp attack becomes slurred and muddy or worse, strident and brittle.
thEQred changes all that, providing profoundly punchy lows and airy, silky smooth highs like no other. It preserves the time relationships of harmonics, which translates into a smoother top end, sweeter and bigger midrange, and a clearer, more distinct bottom when compared to phase shift–style EQs. The resultant sound seems less processed, more like what should have naturally been captured by the microphone. You won’t get those punchy transients and silky highs with analog outboard or any ol’ IIR digital.

Versatile VariSlope

In addition to all the user–centric features that MAAT brings you, like Panorama mode and Contribution controls, thEQred features VariSlope™ technology, proprietary to thEQr. With VariSlope, shelving and cut filters offer continuous adjustment of any slope in the range from near 0 to 24 dB/octave. Unlike other EQs that let you define or draw the curve, VariSlope offers unique versatility while preserving the sound quality MAAT EQs are known for.
The exclusive VariSlope filter technology lets you dial in continuous slope filters that emulate any critically damped shelf in the range from 1st to 4th order, including all imaginary filters in between. “Imaginary” because critically damped filters offer only slopes in discreet 6 dB/octave steps per “order”: 6, 12, 18, 24 et cetera. Our continuous slope low and high cut filter performs similarly, yet you can continuously change its slope from a critically damped 4th order equivalent, through 3rd, 2nd, and 1st order down to zero. The critically damped VariSlope high cut mirrors the continuous slope VariSlope low cut.
Such “in–between” frequency-response filter characteristics, especially with slopes less than 6 dB/octave, are absolutely impossible to implement with classical filter technology. The only workaround would be to cascade many 1st order filters with specially weighted amplitudes to get the overall amplitude envelope lower then 6 dB/octave. Such kludgy filters, however, deliver a wavy frequency response characteristic and are tainted with nasty phase shift and group delay. Quite the opposite, our VariSlope filter affords very smooth, controlled spectral changes without any phase shift.

thEQred works strictly in the frequency domain, while sounding a bit softer than her linear phase sister, thEQorange. Performing at up to 384 kHz, which extends resonant frequency settings up to 80 kHz, it’s perfect for high resolution DSD, DXD and game audio post–production. Its calculations are stored at 80 bits of precision, way more than 32 bit commodity EQs and more than what even fancy 64 bit EQs manage. The result: the construction of your composite filter is impeccable, with vanishingly low THD and without loss of very low amplitude detail.

Vive La Différence

What are the differences between thEQorange and thEQred? We recommend thEQo for “surgical” work, mostly negative gain EQs to address issues in a mix during mastering when material needs to be “fixed” because it has a problem. On the other hand, thEQred is best at aesthetic work, artistic equalization that makes material sound better without affecting the time domain. As with thEQorange and both being linear phase, thEQred doesn’t leave a signature on the sound the way thEQblue does. Because it’s minimum phase not linear phase, thEQblue is for when you would reach for an analog EQ, but with ultimate fidelity that can’t be achieved with analog. So, the three of them together replace all EQ use cases, unless you want distortion, and thEQblue with its 12 Architectures replaces all analog EQs one might want.
thEQred also has VariSlope, something we think is unique in the industry. So, in keeping with that aesthetically minded approach, with thEQred, you can do really broad or really gentle lifts or suppression, as well as all the “normal” stuff you’d expect from a fixed–order EQ. Most engineers think that all equalizers are both problem solvers and artistic. To that we say, “When all you have is a hammer, everything looks like a nail.” Grab a copy of both thEQred and thEQorange, then listen to both side by side. I think you’ll hear why we think of them differently.
If you can afford only one of our thEQ products, it’s probably best to go with thEQblue. Its versatility is unsurpassed. If, however, you work with a fair amount of acoustically recorded performances and higher fidelity recordings, then over time you will find both thEQorange and thEQred indispensable. Specifically for that, we have the annual thEQlp (Linear Phase) subscription, which includes both thEQorange and thEQred.

Asymmetry Banished

Experts say that most digital EQs don’t sound like their analog antecedents, especially when working with baseband 44.1 or 48k sample rates. Spectrum modifications of high frequencies sound unbalanced. The reason is so–called “frequency warping,” which makes bell shapes asymmetric, while high shelves and cuts exhibit steeper slopes than expected. In thEQred, special corrections have been applied, making them look exactly like their analog counterparts while yielding a smooth analog sound.

If One is Good, Isn’t Two Better?

People have asked us why we haven’t included alternative modes like minimal phase and all the other options you find in competing products. Our goal as plug-in designers is to create tools from the user perspective, offering just enough flexibility with a carefully chosen set of options so the user can focus on the job at hand. It would be easy to add dozens of additional options to the preferences window but why? That’s what thEQblue is for, a whole box of “colors”! As a mastering engineer, you need specialized tools which do a particular job in the fastest and best possible manner.
thEQred is a perfect example of just such a tool. Dr.s Musialik and Hatje have already worked through an extensive refinement process. When asked about this, Musialik stated that “…the optimization and refinement of our algorithms was a very long, tedious and iterative procedure between research, development and feedback from experienced mastering engineers. Unfortunately, in high res audio, not everything is measurable or provable by numbers. This is especially true for the measurement of dynamic behavior and reactions to real–world, complex signals.”
Musialik emphasizes that “There is no ‘best’ audio tool for everybody.” His advice: Perform your own listening tests, then select which instruments you want to include in your kit.

Learn More

In this video, Friedemann discusses the differences between our three mastering equalizers

Watch it directly on YouTube

thEQred 線性相位均衡器


直接在 YouTube 上觀看。

thEQred Use Case

This article by John E. Johnson, Jr. discusses thEQred being used in home hi–fi setups.

Download — thEQred User Manual

The user manual PDF includes lots of useful info, check it out…

Reviews & Testimonials

Robert “Bob” Olhsson — legendary indy engineer (Smokey Robinson, Temptations, Steve Roach, Marvin Gaye)

“The ability to recall projects is very important to me and to my clients, so I started moving my signal processing…to Pro Tools and needed to bid goodbye to the (legacy) Algorithmix plug-ins. It turns out I was not alone in wishing for new compatible versions of these extraordinary plugins.
What I love about thEQred is being able to combine this utterly transparent equalizer with my (outboard) hardware. It simply doesn't screw anything up while adding whatever EQ tweaks I can imagine. Also, the continuous-slope shelving is pretty amazing, especially with very natural sounding acoustic recordings.”

Charles “Chip” Reardin – indy engineer (Gary Katz, Sylvia McNair, Straight No Chaser)

“Absolutely stunning EQ. Really. I am very picky, and I've been searching for an ITB EQ of this quality for SO many years. Hats off!…
I've always cringed at the side-effects of high-passing or notching on a mixbus or master with virtually all VST EQs (unless the mix really calls for it, obviously). Orange was the first plug-in I've heard that didn't instantly degrade the mix (and I've tried most if not ALL). Then Red, SO sweet on the highs. Don't think twice about using these on a master! Thanks again for providing these excellent EQs. Orange and Red are just unparalleled ITB EQs IMHO.”

Eddie Grey - engineer & Logic Pro maven

Here’s a video overview of our thEQ family with audio examples.

Praise for the original Algorithmix LinearPhase PEQ Red

thEQred is a modern restoration of the original Linear Phase PEQ Red from Algorithmix. Thanks to improvements in technology since “Red” was released, our new version exceeds the already legendary fidelity of the original. Plus, we’ve added key new tech to the User Experience (UX) to make your time with thEQred easier and more pleasurable.

Robert “Bob” Olhsson via GearSlutz

“I still use blue and red…Blue and red remain unsurpassed sound-wise.”

Sakis Anastopoulos, Digisound Mastering

“I must tell you that I am absolutely ecstatic with the results that I have been achieving with the linear phase EQs…Both Red and Orange EQs have absolutely replaced every other EQ that I own and have given me the ability and freedom to perform challenging frequency adjustment tasks in every project that I master no matter how challenging or what genre it is…Their ability to resolve with accuracy, clarity and musicality, frequency ranges in complex music passages is astonishing, allowing the mastering engineer to focus on the project and forget the artifacts that are usually associated with this kind of processors.”

Graemme Brown, Zen Mastering

“I have spent most of my time with the red version of the LinearPhase PEQ and can honestly say that it is the best sounding software EQ that I have ever heard!”

Bob Katz, Digital Domain

“…the Algorithmix Red and Orange Linear Phase equalizers are must haves.”

Alan Silverman, Arf! Digital

“The depth and punch of the lows and the air and silkiness of the highs are by far the best by far in my experience. A new benchmark…This has now become my default high and low EQ. Chaka (Khan) said the CD sounded incredible and her producer said the lows and highs were ‘amazing.’”

Eric James, reviewing in Sound On Sound magazine

“Red offers totally transparent control of the whole sonic spectrum. Red’s Continuous Slope function on shelving filters is very useful, especially in mastering…Algorithmix's Red mastering EQ is comparable in quality to the best digital hardware units at a fraction of their price.”

Christian van Caine, sound designer (Dreams of Las Vegas, Support Group Olympus, Reya)

“Been demoing Red for a few days now and owned Orange since not long after release. They complete each other beautifully! Fantastic on their own, together the most three-dimensional sound I’ve ever heard”

T-Dogg on our Dr. Christoph’s chops (via GearSlutz)

“The real gurus in the field…Dr. Christoph Musialik, etc. have far surpassed these textbook algorithms…Simply put, genius–level R&D and know–how is priceless.” We concur and know that you will too!

Engineers & Reviewers! Want to add your voiceover to the mix?

Head to our Contact page and give a shout…We’d love to hear what you think!

Speeds & Feeds

Downloads, Features & Specifications

Stay Current

Looking for the latest version of your software? Just download and install the demo! The installer will update everything and your license will take over when you next use the product.


• Download the user manual for thEQred here


  • Fully parametric linear phase EQ
  • Free of group delay
  • Exclusive Contribution Control
  • Unique VariSlope with continuous slope, from near 0 to 24 dB per octave
  • Optional live spectrogram
  • AutoGain for effortless A/B comparisons
  • Variable resonant ƒ tunings for common Western scales
  • Inbuilt tone generator for quick spectral navigation


  • AAX Native (Pro Tools 10.3.10 and newer), AU, VST 2, VST 3
  • Sample rates from 44.1 to 384 kHz
  • pluginval_logo  Verified by pluginval, passing with a score of 10 (the highest strictness level)


VST PlugIn Interface Technology by Steinberg Media Technologies GmbH


Perpetual: One–Time Buyout


  • macOS 10.9 and newer, 64 bit only
  • Windows 7 and newer, 32 & 64 bit
  • OpenGL 3.2 or newer

Order thEQred Now

• thEQred Perpetual License: $489
• thEQlp Linear Phase Subscription: $119, Annual Renewal

[thEQred + thEQorange, $9.92 per month billed annually]
• All EQ Big Bundle: $1099, $557 Total Savings
[25% Off thEQblue12, thEQred, thEQorange + free SantaCruzEQ6]