Elastika is a stereo synthesis filter based on a physics simulation. There is a pair of left/right audio input jacks, and a pair of left/right audio output jacks.
Here are some videos that offer a peek at Elastika. Headphones are recommended to best experience the stereo field.
Omri Cohen made this "Quick Tip" video about using Elastika for metallic percussion sounds:
Here I demo feeding a simple square wave into Elastika to produce a gong-like sound:
In the next video, Seaside Modular's Proteus generates a melody that is fed through Elastika, producing a texture that starts out like a steel drum and ends up more like electric guitar distortion:
This video shows Elastika producing sounds on its own without any audio input. It is possible to tune it into self-oscillating modes that sound a little like a flute or recorder, then more like a trumpet. Parts of this recording are reminiscent of tuning a shortwave radio. Starting around 3:30 are some more chaotic and drone-like sounds.
Here is another example of a generated sound texture. Using Instruo ochd to slighly permute the settings, Elastika exhibits indefinite reverberation while subtly changing texture throughout.
Ambient musician Virtual Modular created the following video where he combines Elastika with Infrasonic Audio's Warp Core oscillator to produce some really nice sound textures.
Albert Yeh created some fun polyrhythms fed through multiple instances of Elastika, used for percussion:
Understanding the inner workings of the simulation is helpful for intuitively tuning Elastika's many control inputs.
The physics model includes a network of balls and springs connected in a hexagonal grid pattern.
There are three kinds of components in the Elastika physics model:
- Anchor: A point in space that stays locked in one location. Anchors do not respond to any forces acting on them. However, two of the anchors are used for injecting input audio into the model. These anchors are moved back and forth in response to input voltages.
- Ball: A mobile point mass. A ball has a positive finite mass, an electric charge, a 3D position vector, and a 3D velocity vector. A designated pair of balls determines audio output. The stereo output is based on the physical movement of these two output balls.
- Spring: An elastic rod that connects one ball with another, or one anchor with one ball. The springs have two parameters that control their behavior: stiffness and span. The stiffness parameter adjusts how much force it takes per unit change in the length of the spring. Span is the rest length at which the spring exerts zero net force. The force is applied equally to both balls, in opposite directions, in accordance with Newton's Third Law.
On each audio sample, audio voltages are fed into the network by adjusting the positions of the left and right anchors. Then the force vectors on each ball are calculated based on an ambient magnetic field and the orientation and length of the three springs connected to it. The net force vector causes an acceleration on the ball using Newton's Second Law: F=ma.
Every ball's acceleration is then used to update its velocity and position vectors for that time step. The simulation proceeds time step by time step. An adjustable amount of friction is also applied to gradually dampen the kinetic energy of the system.
This diagram shows the structure of the Elastika physical model.
- The magenta spheres around the perimeter are anchors.
- The teal spheres on the interior are mobile balls.
- The lines that connect anchors to balls, and balls to each other, are springs.
The anchors that are used for left and right inputs are labeled L/in and R/in. The input anchors are forced to move in response to applied input voltages.
The balls labeled L/out and R/out are the stereo audio outputs. The movement of these balls is determines the voltages for the stereo audio output channels.
The balls marked Lm and Rm are mass impurity balls whose masses are varied by the MASS slider as described below.
The following controls have sliders for manual control, along with attenuverters and control voltage (CV) inputs for enabling automation.
All attenuverter knobs in Elastika support a low sensitivity option, which is often helpful for making CV control easier to adjust.
- FRIC: the friction force that slows down vibration in the simulation. Low friction is similar to increased reverb. The higher the FRIC setting, the shorter the vibration lasts before coming to a halt.
- STIF: adjusts the stiffness of the springs, which is the amount of force per unit length of the spring when stretched or compressed away from its rest length. Higher stiffness generally creates higher pitched sounds.
- SPAN: adjusts the rest length of all the springs. It is possible for the span to be shorter than the initial distance between the connected balls, which results in a bell-like quality. Also, span can be made longer than the initial ball distance, in which case the network tends to "explode" and vibrate in a more chaotic manner as the surface becomes loose and convex.
- CURL: In addition to the springs pushing/pulling on the balls, there is an adjustable magnetic field. The balls have an electric charge, and as they move through the magnetic field, it causes a force perpendicular to both the ball's velocity and the orientation of the magnetic field lines. This tends to cause the balls to move in circular or helical trajectories. When the CURL knob is set to a positive value, it induces a magnetic field in the x-direction, which is parallel to the plane of the hexagonal mesh. When the CURL knob is set to a negative value, the magnetic field is aligned in the z-direction, which is perpendicular to the mesh. At zero, CURL completely turns off the magnetic field. As CURL is moved away from zero in either direction, the magnetic field gets progressively stronger. Extreme values of CURL tend to destabilize the mesh and create a harsh sound. With careful tuning, interesting effects can occur.
- MASS: There are 22 mobile balls in the simulation. Of these, 20 mobile balls have a common fixed mass. The two remaining balls have an adjustable "impurity" mass. The MASS slider controls the mass of these two balls in tandem. The MASS slider ranges exponentially from 0.1 to 10.0. The center and default mass value is 1.0, which makes the mass impurity balls have the same mass as all the other mobile balls. Tuning the impurity mass can allow for some interesting chaotic and/or multi-resonant modes, especially when combined with the CURL adjustment.
At the top of the panel are two larger knobs that control tilt angles. There is one tilt angle for the input and one for the output.
The input tilt angle knob controls the direction in 3D space by which the left and right input balls are vibrated in accordance with the input audio. When set to 0°, the vibration direction is perpendicular to the plane of the hexagonal grid. When set to 90°, the direction is parallel to that plane. The default angle is 45°.
Similarly, the output tilt angle knob controls the direction in which output audio is derived from the movement of the output balls. Like the input tilt angle, the output tilt angle range 0° to 90° makes the output sensitive to movement angles going from perpendicular to the hexagonal mesh to parallel to it. The default angle is 45°.
Just like the slider controls, the tilt knobs come with associated attenuverters and CV inputs, for helping automate tilt angle control.
Lower tilt angles tend to introduce deeper bass components to the sound because the resonant frequency of the mesh in that direction is lower. As tilt angles increase toward 90°, response tends to emphasize higher frequencies, as it resonates more closely with individual ball-to-ball spring vibrations.
The knob at the bottom left marked IN adjusts how strongly the input stereo signal drives the input balls.
The knob at the bottom right marked OUT adjusts the volume level of the stereo output signal.
Independent knobs are provided because their effects are not the same. The OUT knob simply adjusts the volume level of the output. This is important because Elastika is a complex simulation with a wide variety of behaviors. It is hard to tell in advance how loud a sound it will produce, so there needs to be a way to reduce its output when too loud, or to amplify it when too quiet.
The IN knob also has some effect on the output level, but it mainly controls how much the shape of the mesh is distored by the input. Rather than simply getting louder or quieter, adjusting IN can also affect the quality of the sound.
Sometimes it is interesting to increase IN and decrease OUT, or vice versa, to explore different nuances of sound.
Elastika's context menu looks like this:
Elastika includes an internal DC rejection filter on both audio outputs. This filter prevents contaminating the output with DC bias. Some people find adjusting the DC cutoff frequency useful as a simple equalization tool. When Elastika is tuned to output deep bass audio, increasing the DC rejection frequency can help reduce a "muddy" tone.
To adjust the cutoff frequency, right-click on Elastika to open its context menu. At the bottom of the menu is a "DC reject cutoff" slider that you can move left or right to set the cutoff frequency anywhere from 20 Hz to 400 Hz.
Elastika's physical model can produce a surprisingly wide range of output voltage levels. The amplitude can be hard to predict, so as a safeguard, Elastika includes an output limiter that uses automatic gain control to keep the output voltages within a reasonable range.
The limiter can be enabled or disabled. When enabled, it can be set to any threshold level between 1V and 10V. When the limiter is enabled, it will adapt automatically to output voltages higher than its threshold by quickly reducing output gain. If the volume gets quieter than the level setting, the limiter allows the gain to settle back to a maximum of unity gain (0 dB). This means the limiter never makes the output louder than it would be if the limiter were disabled.
By default, the limiter is enabled and is configured for a 4V threshold. Using Elastika's right-click context menu, you can slide the limiter threshold left or right anywhere from 1V to 10V.
If you move the slider all the way to the right, it will turn the limiter OFF. Disabling the limiter like this can result in extreme output voltages in some cases, but it could make sense for patches where Elastika's output is controlled by some external module, such as a mixer with a very low setting. Most of the time, it's a good idea to leave the limiter enabled, to avoid extremely loud sounds and clipping distortion.
When Elastika's limiter is enabled, and the output level is so high that the limiter is actively working to keep it under control, the sound quality will not be ideal. Therefore, Elastika signals a warning by making the output level knob glow red, like this:
This is a hint that you might want to turn down the output knob a little bit, or do something else to make Elastika quieter, in order to eliminate any distortion introduced by the limiter. Of course, you are the judge of sound quality, and you may decide to ignore the limiter warning if you are getting good results in your patch.
If you disable the limiter, this is interpreted as a manual override, and the warning light will not turn on.
If you don't want the warning light to come on, but you want to keep the limiter enabled, there is an option for this in the right-click context menu labeled Limiter warning light. Clicking on this option will toggle whether the warning light turns on when the limiter is active. The warning light option defaults to being enabled.
If a Tricorder is placed immediately to the right of Elastika, it will receive the 3D coordinates of either the left or right output particle. This menu item selects the right ball when checked, or the left ball when unchecked.
See low-sensitivity attenuverters.
Elastika uses more CPU than the typical module in VCV Rack. In cases where you want to use more than one instance of Elastika in a patch, it can be handy to have more control over their CPU usage by turning them on and off at will.
Toward the bottom of the panel, between the IN and OUT knobs, is a power pushbutton. When activated, the button lights up and Elastika is operating and using CPU time. Clicking on the power button toggles between on and off. When the power is off, the button goes dark and Elastika stops producing sound. In this off state, Elastika uses almost zero CPU time. Entering the off state also causes all the balls to return to their starting positions and to have their velocities set to zero. Thus when Elastika is powered back on, it restarts from an initially quiet state.
Beneath the button is a power gate input. When connected, the gate input takes precedence over the power button. The power gate input thus allows you to automate turning Elastika on and off. When the power gate voltage goes above +1V, Elastika will turn on. When the voltage falls below +0.1V, Elastika will turn off. Between +0.1V and +1V, Elastika will remain in the same on/off state. This is known as Schmitt trigger behavior, and is intended to prevent unwanted toggling that could easily happen if a single voltage threshold were used.
Whether you use the power button or the input gate for controlling power, there is an anti-click linear ramp of 1/400 of a second. In other words, when you turn Elastika off, the output volume fades out over 1/400 of a second before turning off. When you turn Elastika back on, the output level fades back in over 1/400 of a second. Thus the maximum speed at which you can cycle Elastika completely on and off is 200 Hz.
The left and right audio outputs of Elastika are each monophonic, although taken together, they create a stereo signal.
Elastika is not polyphonic, but all of its inputs — audio and CV — add up the voltages from the channels to produce a single input voltage. For example, you can connect a polyphonic audio signal to the left audio input, and the sum of voltages will be used as the left channel input.
Likewise, you can use a polyphonic cable to CV-modulate one of the parameters (TILT, FRIC, STIF, and so on). This provides an implicit unity gain mixer, which in some cases could help simplify your patch.
Even the power gate input adds voltages this way, and thus can be used as a simple boolean logic gate. For example, two unipolar gates (each 0V or +10V) can be combined in a polyphonic cable to act as an OR gate. Either gate turning on will turn on Elastika. Or you can use bipolar gates (each -5V or +5V) to serve as an AND gate.