Air-G Prism
User Manual
Version 1.0
Six-band graphic equalizer based on PearEQ by Airwindows.
Original source code released under an open license by Chris Johnson.
User Manual
Version 1.0
Six-band graphic equalizer based on PearEQ by Airwindows.
Original source code released under an open license by Chris Johnson.
Air-G Prism is a six-band graphic equalizer based on the PearEQ algorithm by Airwindows. Unlike a parametric equalizer — which uses resonant biquad-type filters — PearEQ splits the spectrum subtractively: it separates one band, subtracts it from the signal, separates the next from what remains, and so on. At the end all the bands are summed back together, each with its own gain. Set flat, that sum reconstructs the original signal exactly.
The six bands — SUB, BASS, LMID, MID, HMID and HIGH — cover the spectrum from the sub-lows to the highs. Each band has a single gain (GAIN) control and can be enabled or disabled independently. There are no frequency or Q knobs: the frequencies are fixed, like on a classic graphic equalizer. On top of that there is an interactive display that draws the equalizer's true response and lets you drag the curve with the mouse.
It belongs to the same family as Velvet, EaseQ, Clip and the rest of the Air-G line: reimplementations of Airwindows algorithms, with their own interface and additions aimed at mixing and mastering work.
PearEQ does not work like a classic parametric equalizer. It builds the bands by subtracting one at a time: the highs are the signal minus a low-pass; the mids are what remains minus another low-pass; and so on down to the sub-lows. Because each stage is subtracted cleanly, the bands can be summed back together to give a result identical to the original — set flat it is literally transparent, and it stays that way at any setting.
The filtering rolls off steeper and steeper until it cancels, yet it never produces a resonant peak: the bands act “curved”, smooth in character, and with very good isolation between them. It is, in essence, a six-band graphic equalizer — though one with plenty of authority.
Chris Johnson describes it as “basically a six-band graphic, and it sounds very much like a six-band graphic.” Its strength is the isolation: you can, for example, pull out the low-mids completely and hear elements emerge that were buried before. The SUB band is the octave below the bass — almost entirely below 40 Hz — and is so well isolated that it can be controlled on its own. And even taken to extremes, “it adds up to perfectly flat if you leave it flat”: the sound stays coherent, like a single piece.
Air-G Prism interface.
All six bands work the same way. Each one has two controls: a large GAIN knob and a round ON/OFF button. There is no frequency knob — in PearEQ the frequencies are fixed. Understand one band and you understand all six.
The large knob in each sector. The neutral point (0 dB, flat band) is at the center: turning right boosts the band, turning left cuts it. Below the knob, a label shows the real dB that band is applying, measured directly from the equalizer's response.
Unlike a gentle EQ, PearEQ is powerful: a single band can boost by around +12 dB and cut down to nearly −24 dB; the six together reach about +16 / −27 dB. The curves are wide and musical, but with real authority — a small move already works an entire region of the spectrum.
The round button to the right of each GAIN knob switches the band on or off. When a band is off it stays flat (0 dB), as if it were not there, but it keeps its knob position: switching it back on restores exactly the setting it had. The change is smooth, with no clicks. On the display, a disabled band shows its node in gray.
The dB number under each GAIN is not a rough calculation: it is obtained by measuring the plugin's true response in the band's region. That makes it the most faithful reading of how much each band is really working, including the interaction with its neighbors.
In PearEQ the bands are not bells you can slide around: they are adjacent slices defined by fixed crossover points. Moving one of those frequencies would only steal range from the neighboring band. So, just like on a graphic equalizer, the frequencies are fixed and the whole tone is shaped with the six gains.
The six bands cover the spectrum from the sub-lows to the highs, in contiguous slices with very good isolation between them. From the bottom up:
The lowest octave (largely below 40 Hz), very well isolated. It controls the sub weight — the part you feel more than hear — without touching the rest of the lows. Watch out on small speakers or headphones: there may be a lot of energy here that you are not hearing.
The punch and the body: kick, bass, the low fundamentals. PearEQ has a very powerful low end; boosting adds weight, cutting cleans and clears.
The body and warmth of vocals, guitars and snare. Too much sounds “boxy” or nasal; too little and the mix thins out. This is the ideal band to remove “mud” without touching the punch of the bass.
The center of the mix. A good deal of the presence of vocals and instruments lives here; it is the region that most pushes elements forward or back. Touch a little, listen a lot.
Presence and definition. It is the region the ear is most sensitive to: here you gain attack and intelligibility, but it is also where harshness and fatigue appear fastest if overdone.
Brightness and air. It opens the mix and adds clarity to cymbals, strings and consonants. Boosted in moderation it brings life and openness; in excess, sibilance and harshness.
Unlike shelving EQs that overlap heavily, Prism's bands are contiguous slices with steep crossovers: they isolate remarkably well. That allows “surgical on a large scale” moves — removing a whole region (the low-mid or the sub-lows, say) and hearing the rest open up — while still sounding musical, because set flat everything sums back smooth.
The graph in the top panel is not an approximate illustration: it draws the equalizer's true frequency response, measured directly from the processing. What you see on the display is exactly what happens to the audio — it matches an external analyzer. The horizontal axis is frequency (from 20 Hz to 20 kHz, with its values marked) and the vertical axis is dB.
The dB scale adjusts itself so the curve is never crushed against the edges: with large moves the axis grows; with subtle ones it zooms in. On the left, the lines mark the reference dB.
On the curve there are six nodes, one per band. They can be dragged with the mouse, but only vertically:
Moving a node moves the corresponding knob and vice versa: they are the same control seen two ways. It is the most direct way to draw the tone — grab the node of the band you want to work on and raise or lower it until it sounds right. A node shown in gray means that band is off.
The curve is recalculated only when you move a control, not continuously, and that calculation happens outside the audio engine. Drawing the true response adds no load to the sound processing: the plugin is just as light with the display open or closed.
Prism's natural ground. Like a graphic EQ: a touch more BASS for body, a bit of HIGH to open up, a slight dip in LMID to clear things. Ideal for the overall spectral balance of a track or a bus.
Boost the high bands and cut the low ones — or the other way around — to tilt the whole balance. Combining several contiguous bands, the move comes out wide and very musical, without sounding processed.
Use Prism's isolation to pull out a whole band — LMID to clean up mud, say, or SUB to tame rumble — and hear the rest of the mix open up.
A trick from the author himself: boost SUB and BASS together with HIGH, and scoop the mids a little, for a deep-lows + airy-highs effect. The SUB band lets you dose the sub without muddying the bass.
Prism is a powerful six-band graphic EQ with character. Set flat it is transparent; pushed, it gives wide curves with authority and an uncommon degree of isolation between bands. The node display invites you to work “by eye and ear”: raise or lower each band's node until it sounds right, trusting that what you see is exactly what you hear.
It is a tool for shaping and adding character — tilting, adding body, opening up, isolating whole regions — rather than for pinpoint corrections. If you want an EQ that shapes broadly and organically, without losing coherence even at the extremes, Prism is exactly that.
Air-G Prism was developed by Air-G Audio as part of its line of plugins based on the work of Airwindows.
The PearEQ algorithm is the work of Chris Johnson (Airwindows), whose original source code is released under an open license at github.com/airwindows. Air-G Prism is a faithful reimplementation of the original algorithm with its own additions: independent per-band enable, gain labels measured in real time and an interactive display that draws the true response with draggable nodes.
To Chris Johnson for his tireless work on Airwindows and for sharing decades of audio processing research completely openly.
Air-G Prism v1.0 — Air-G Audio. The PearEQ algorithm is the work of Chris Johnson / Airwindows and is used under the terms of its open license.