Undertone Audio MPEQ-1 [WiN]

• Product: MPEQ-1
• Developer: Undertone Audio
• Version: 1.0.0
• Format: VST3, AAX
• Requirements: Windows 7 or later
• Source: digital.undertoneaudio.com/products/mpeq-1-plugin

The MPEQ-1 plugin is a four-band parametric equalizer with per-band saturation and a Vari-Phase mode, ported from Undertone Audio’s Class A rack EQ. Each band runs its own selectable distortion stage — three drive types with independent level control — layered after the EQ curve rather than at the input. Shape control blends a band between peak and shelf response on a continuous dial, not a stepped switch. Phase mode lets a band invert and reintroduce a filtered slice of signal past the null point, shifting phase relationships in one frequency range while leaving the rest of the spectrum untouched. The plugin carries no preamp or transformer stage — the mic pre and DI section from the hardware unit are not part of this build. Searches for a parametric EQ with built-in band-specific saturation control land here.

Key Takeaway

Activated when a mix needs harmonic coloration tied to a specific frequency band rather than applied across the whole channel — drive on a vocal’s presence range without touching the low end, for example. Displaces a separate saturation plugin stacked after a clean EQ. Phase mode only affects program material with overlapping mic sources at different distances from the source; single-source tracks won’t expose it. Engineers who only need transparent correction EQ can skip the saturation stage entirely and run it clean.

Per-Band Saturation, Independent of Curve

Each of the four bands carries a dedicated distortion stage with three selectable drive types and a level control specific to that band. Driving the high band into saturation while leaving the low band’s gain stage untouched produces harmonic content concentrated in the range that band is already shaping — the low end keeps its EQ curve without picking up added harmonics. This separates from a single broadband saturation stage, where drive characteristics on one frequency range bleed into all the others.

Pushing a snare’s fundamental band past unity gain adds weight and grit to that specific range while the top end’s band stays clean, so cymbal bleed in the same track doesn’t pick up distortion meant for the drum body. The tradeoff is setup time: dialing in four independent drive amounts per track takes longer than running one saturation plugin across the whole signal. Engineers working fast turnaround sessions may find the per-band control more granularity than the timeline allows.

Shape Control: Peak to Shelf on One Dial

Shape blends a band continuously between a peak curve and a shelf curve rather than switching between fixed modes. Turning shape partway introduces a slope shaped between the two — narrower than a pure shelf, broader than a pure peak — which lets one band cover ground that would otherwise need two separate bands stacked. This replaces the workflow of reaching for a second EQ instance just to get a shelf-like tail on a peak boost.

The control doesn’t label its intermediate positions with numeric values, so matching a shape setting across two tracks by ear takes more attention than copying a numeric Q or gain value would. Producers doing recall-heavy sessions across multiple songs may want to log shape settings manually rather than relying on visual matching.

Vari-Phase: Null-Point Blending Past Zero

Phase mode filters the signal, inverts it, and blends it back in past the cancellation null point, so a chosen frequency range can have its phase shifted relative to the rest of the spectrum while everything outside that range stays untouched. This addresses comb-filtering between multiple mics on one source — a room mic and a close mic on the same drum, for instance — without resorting to time-alignment or moving the mic.

Pushing the control past the null point on a low band can change how a kick’s fundamental sits against a room mic without touching either signal’s gain. The control requires comparing both mic sources in context to hear the effect; soloed, a single source won’t reveal what phase mode is doing, since there’s nothing to interfere with. Mixers working from a single-mic source per track won’t have a use for this control on that track.

Notch Mode for Surgical Cuts

Switching a band into notch mode narrows the filter into a deep, narrow cut rather than the broader proportional-Q reduction used in standard EQ mode. This targets a resonant frequency — a ring in a snare shell, a room mode in a vocal booth — without pulling down the surrounding spectrum the way a wide-Q cut would.

Combined with the Shape control, notch mode can be widened slightly past a pure notch into a narrow dip, useful when the offending frequency drifts slightly across a performance rather than sitting still. The control only goes one direction — cut — so shaping a narrow boost in the same way isn’t available in this mode; that has to happen in standard parametric mode on a separate band.

Saturation Style Selection Per Band

Three distortion types are available per band, each producing a different harmonic profile, selectable independently from the level amount. Choosing a different type on each band — softer harmonic generation on a vocal’s low-mid band, a more aggressive type on a guitar’s presence band — lets one plugin instance handle multiple coloration characters across a single channel’s frequency range.

The selection happens per band rather than globally, so changing a track’s overall character means revisiting each band individually rather than adjusting one master type control. Tracks needing a single consistent saturation character across the whole signal may be faster to handle with a single broadband saturation plugin instead.

FAQs