Back from the grave

Electromechanical Effects

A side project for us has been the development of audio effect algorithms… this is no longer synthesis, but still physical modeling of a kind. In this case, there is always an audio input of some kind.

An interesting class of effects is the electromechanical family including, for example, plate reverberation (such as the famous EMT series plate reverbs) and also the cheaper, more common and also distinctive-sounding spring reverberators.

Plate reverberation has been approached by two of our postdoctoral researchers, Dr. Michele Ducceschi and Dr. Craig Webb, using modal techniques; they’ve managed to get a fully physical plate reverb running in real time, and, in fact, you can download the beta version at the website of our spinout company Physical Audio. It allows for control over plate dimensions, material, as well as readout positions (stereo), and parameterised control over frequency-dependent loss.

A spring reverb imparts a reverberant effect to a sound which has some characteristics of real room reverberation (the original intention) including various series of echoes, as well as a noise-like late response. Factors such as the helix angle, total wire length and wire radius have a big impact on the echo densities, as well as on the placement of one or more cut-offs in the resulting spectrum!

As with all the systems we study in the NESS project, we employ time stepping methods (in this case FDTD) in order to numerically solve the system, giving a complete representation of the dynamics of the spring, as illustrated on the right.

Sound quality is rich… here is a typical impulse response:

In any case, for more on this approach to spring reverberation, see this paper.