Spring Reverb For Macs

Physical Audio's PA4 models wave propagation in helical springs      14/11/18

Physical Audio tells us that PA4 is an AU reverb plug-in that uses numerical modelling to create a fully-customisable spring reverb. Here’s the story in their own words…

PA4 Dual Spring Reverb is the first ever plug-in to model wave propagation in helical springs. The audio engine is built entirely upon the simulation of the inherent physical equations, without any approximations. This gives innovative control over the springs, and allows new sonic textures. PA4 will sit perfectly on your guitar, vocal, and drum mixes, adding dripping tones with a colourful spectrum.

We chose four perceptual parameters to describe a spring. Firstly the Echo Time and Spread, which set the time of the initial chirps and how much the following chirps deviate. The Cutoff sets their highest frequency, whilst the Boing controls the 'sharpness' of the spring sound. Design a spring to suit your material, then apply the offset control to create natural stereo depth.

The T60 decay times of the springs are controlled using real-time multi-band parameters. The chirp modes have low, mid, and high frequency bands which operate up to the cutoff. A second set of modes which affect the whole frequency spectrum are controlled by the Shimmer decay. This is most obvious above the cutoff, where it adds a mid to high frequency 'shimmer' to the sound.

Our modelling starts from a mathematical description of wave propagation in elastic helical structures. The physical properties such as length, wire radius, and pitch angle are then mapped to the perceptual parameters as detailed above. From there we create a discrete modal system with up to 4,000 modes for each spring.

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