In this post we examine the resonator section of our physical modelling instrument Derailer. The plugin uses mathematical models of three basic elements; stiff strings, metal bars, and nonlinear springs. The resonator uses the metal bars which can be connected together using the nonlinear springs. There are five bars and up to ten springs that can be used to form a network of sympathetic resonance. The user interface of the plugin has 2 views, one for the Driver and one for the Resonator. The Resonator View The bars and springs that form the resonator are shown on the left-hand side of the UI. This is an interactive view. You can select bars or springs by clicking on them and you can move springs along a bar by dragging their end points. The parameters for the currently selected bar and spring are shown in the top-right quadrant. You can also use the +/- buttons to cycle through them. The parameters for each are as follows. Bar parameters: – Rigidity (%)– Sustain (sec)– Tone (%)– Mass (relative) Spring parameters: – On / Off– Stiffness (%)– Nonlinearity (%)– Decay (%)– Location These parameters can be varied independently for each bar and spring. They can also be randomised using the Rand button, and the lock icon can be used to hold the settings of a bar. In addition, there are global controls for the stiffness and nonlinearity of the springs in the bottom-right quadrant. These are multiplying factors which adjust the individual settings on each spring. They are assigned to MIDI cc27 and cc28. All of these parameters are real-time controls, with the exception of the bar rigidity, spring On/Off and spring location which react to mouse-up the UI and perform a fast reset. The resonator input controls determine the point at which the driver signal is fed into the resonator. The sweep control adds a dynamic movement of the input position along the selected bar. Finally we have output mix gain controls for each of the bars, as well as the driver signal. Basic bar strikes So here’s the resonator in its most basic form, with no springs connecting the bars together. Note that Bar 1 has a lower rigidity range than the other bars. Two connected bars Now let’s connect bar 1 and bar 2 together using a spring and see how moving the position changes the resonance. We’ll then increase the nonlinearity in the spring and vary the stiffness. Spring nonlinearity The nonlinearity in the springs can give rise to all kinds of interesting tonal effects. In this next example we are driving the resonator with the basic sawtooth, mostly just holding a C3 with occasional C2 notes. Without doing anything else the resonator gives a wide range of different timbres as the continuous excitation interacts with the nonlinearity in the springs. This is using just 3 bars and 4 springs. Fully-connected systems Finally here’s a system with all 5 bars connected together. It uses a bowed string excitation as the driver, being fed into bar 1. We’ll use the global spring controls to get dramatic changes in the timbre by varying the stiffness and nonlinearity. So that concludes our look at the resonator section of Derailer.