Physical Audio Tetrad Synthesizer plugin combines slashed metal plates with hybrid synthesis

Physical Audio Tetrad is a new Synthesizer plugin that combines physical modeling and granular synthesis to feed four modeled metal plates. 

This week has already been quite eventful when it comes to Synthesizer plugins. Acustica Audio showcased the Expanse-5, UAD the Anthem, and Cherry Audio its ARP Odyssey emulation ODC 2800. And let’s not forget the free Synth One J6 for iOS. The week isn’t over yet, and there’s another new synth.

Physical Audio, a British developer that still flies somewhat under the radar of many, has exciting physical modeling synthesizers in its portfolio. The latest Physical Audio development is called Tetrad and is just as special and different as his other synths. 

Physical Audio Tetrad

Tetrad was developed in collaboration with experimental musician Gadi Sassoon, whose ‘Sculpture-based synth’ installation makes use of slashed metal plates and synthesis processes. Physical Audio has taken this concept and packed it into its new softsynth Tetrad.

The engine is very unusual and unique. At its core is a quad oscillator, which can generate four-note chords, four related partials, custom microtonal signals, or more traditional four-oscillator sounds. There is also an ADSR envelope and FM options (frequency/depth) for all oscillator types.

The oscillator signal is then sent through a 4×4 matrix mixer, allowing for blending of different voices into four buses. From here, you can further shape the signal with a classic multimode filter (low-pass, band-pass, high-pass) featuring cutoff and resonance controls.

Things get exciting in the next step. Once your filtering is complete, the signal passes through three distinct processors. The first is the Quad AM module that takes the four input buses and modulates their amplitude.

With parameters such as phase offset, depth, shape, and rate, you can separate the four signals in time. This allows you to create a wide range of rhythmic effects, pseudo-arpeggios, and pseudo-sequences. After this first stage, you can switch on another multimode filter if necessary. 

Granular Meets Slashed Metal Plates

The amplitude-modulated signal then flows into a granulator optimized for quad sound. Granular synthesis now comes into play. It offers classic controls such as grain size and shape, pitchshift, add jitter to the window position and feedback.

Exciting is here that that his process can be done on four signals at the same time. You can also set a different grain size and pitch per input bus, adding more complexitiy. Plus, there is a sync and a reverse option for the grains. And yes, behind the granular wall there is another multimode filter that you can switch on.

The developer has saved the best for last, or let’s say the more special part of the plugin, the Quad Plates module. It sends the quad signal into four physically modelled plates aka resonators, each slashed to give a different mode of vibration. They can be driven and positioned different graphically on the virtual sound stage.

You can also fully modify these smashed plates using various parameters: dry/wet mix, plate decay, metal cuts, and preamp drive. That’s not all of the sound desing fun.

Modulation

It also host an impressive modulation engine with eight multiwave LFOs, creative envelope-following sources, MPE, and MIDI controls. All this is managed by a modulation matrix with 40 different engine destinations.

There is also a side-chain input and a quad sound output option, allowing to process them even further for quadraphonic experimentations. The engine is also fully MPE compatible with a glide range of +/- 48 semitones.

To get it started, it ships with 115 presets. I guess you need them to see what’s possible and how the engine works. This isn’t just another virtual analog synth.

First Impression

I’m a big fan of physical modeling synthesizers. Many developers follow a classic concept with exciter and resonator relationships. Physcial Audio is one of the few who has consistently brought new ideas for physical modeling to the table.

With Tetrad, they continue this path. I find the synth concept exciting, as well as the sound it produces. You just have to see how versatile it is. I’m sure it’s not a synth that will appeal to everyone. It’s certainly an experimental synth.

Physical Audio Tetrad is now available for an introductory price of £47 / $59 / 47€ + VAT, instead of £79 / $99 / 80€ + VAT, until July 27, 2025. It runs as a VST3, AU, and AAX plugin on macOS (native Apple Silicon + Intel) and Windows.

More information here: Physical Audio

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