Sculpture string parameters in Logic Pro for iPad

The string is responsible for the basic tone of your sound. You can define its material—what it’s made of—with the Material Pad, and can determine its behavior when bowed, plucked, struck, and so on.

The string itself doesn’t make a sound unless it is stimulated—excited or disturbed—by at least one object. Up to three different types of objects are used to excite, disturb, or damp the string (make it vibrate or affect its movement). See Sculpture objects overview.

Sculpture’s string and the excite/disturb objects are similar to the oscillators in traditional synthesizers. The string is considerably more sophisticated in concept than simple oscillators, however.

In essence, you’re creating the waveform, or base timbre, by mathematically describing the string properties, and the properties of its environment. These include, among others, the material the string is made of; the thickness, length, and tension of the string; its characteristics over time; the atmosphere it is being played in (such as water or air); and the way it is being played—struck, bowed, and so on.

Sculpture goes far beyond the mere creation of an infinite number of base timbres, however. One of the key differences between the Sculpture string and a traditional synthesizer waveform is that the base timbre provided by the string is in a constant state of flux. For example, if the Sculpture string is still vibrating for a specific note, retriggering that same note interacts with the ongoing vibration. This is not dissimilar to the effect of repeatedly plucking a guitar string, where the string is still vibrating when the next note is played. This alters the harmonic spectrum each time—which is why acoustic guitars sound organic when a note is played repeatedly, and sampled guitars don’t.

This is quite different from other synthesis methods where the base timbre waveform, even if modulated, does not harmonically interact with currently audible notes when retriggered. What usually happens in traditional synthesizers is that the waveform is restarted—from mid-cycle, or from the beginning—with the result being an increase in volume, or a slight cyclical wave shift.

The string parameters apply on a per-voice basis. A number of parameters can be morphed between up to five morph points. These are indicated in the parameter descriptions. See Sculpture morph overview.

String parameters

Resolution, Media Loss, and Tension Mod can be scaled independently above and below middle C. See Sculpture string parameter scaling.

Resolution knob: Set the maximum number of harmonics contained in (and spatial resolution of) the sound at C3. Changes to the Resolution value alter the interaction of the string with the objects, which has a corresponding effect on overtone frequencies—very low Resolution values result in inharmonic spectra, even with Stiffness set to 0. Higher resolution values enhance the precision of calculations, increasing computer processing requirements. Resolution behavior interacts with the Render Mode buttons, changing the way it behaves.
Render Mode buttons: Choose Basic, Extended, or High Definition mode. Each Render Mode option changes the number of available elements and/or processing.
Sculpture’s string model can roughly be seen as a chain of springs and masses. The maximum number of elements (masses) is set with the Resolution knob. The Resolution control interacts with the pitch, stiffness and pitch bend range settings to automatically set the number of overtones that are actually used. This Sculpture string model affords advantages over the more common waveguide models, especially when it comes to interactions with the string with multiple or larger objects. An inherent property of this flexible string model is that higher overtones are slightly below integer multiples of the fundamental, leading to increasingly inharmonic higher overtones for a string without any stiffness.
- Basic: Choose to set a maximum of 100 elements, with some internal headroom for extreme key scaling. Suitable for many sound types, and has a lower processing load than other render modes. There is a direct correlation between the number of vibration modes and elements, resulting in a maximum of 99 overtones in the spectrum of a single voice. For example, a 100 Hz bass note (with no string stiffness) has a highest overtone of around 10 kHz, making the more audibly inharmonic upper third of the harmonic series fall into the audible range.
- Extended: Choose to set a maximum of 1000 elements. The Resolution knob, coupled with pitch, stiffness and pitch bend range settings affect the number of elements (overtones) used. This mode automatically reduces the number of audible inharmonic overtones until none of the overtones happen at rates above half the sampling frequency.
- High Definition: Choose to set a maximum of 1000 elements and to also turn on internal 2x oversampling, which adds frequency headroom for more overtones. The Resolution knob, coupled with pitch, stiffness and pitch bend range settings affect the number of elements (overtones) used. This mode is significantly more processor-intensive than Extended mode as it runs at double the frequency and allows more elements per string for the same note pitch.
Material Pad: Drag the gray dot to determine the basic tone of the string by setting the stiffness and inner loss (damping) properties. See Material Pad controls.
Media Loss slider: Set the amount of string damping caused by the surrounding media (the atmosphere)—for example, air, water, olive oil, and so on. These losses are independent of frequency. This provides control over the duration of the exponential amplitude decay, after the excitation of the string has stopped. Values above 1.0 cause media losses to increase when the key is released. This parameter can be used to simulate a string that is dropped into a bucket of water after initially vibrating in air, for example. Obviously, this is not what the average violinist would do, but it can be useful for some interesting sound variations.
Note: Both the Media Loss and Tension Mod sliders are set relative to middle C. As you play above or below this note, tuning and other elements of the string can, and will, change.
Tension Mod slider: Set the momentary detuning of the string. Strings, such as those of a guitar, exhibit a particularly prominent nonlinear behavior—if the string excursion is large, the string is detuned upward. Because this detuning is caused by the momentary, rather than the average, excursion of the string, the detuning occurs very quickly. This phenomenon is known technically as tension modulation nonlinearity. Nontechnically, setting or modulating the Tension Mod slider to values above 0 emulates this momentary detuning effect in Sculpture.
Note: This nonlinear effect can deliver surprising results and can also make the entire model unstable, especially when combined with a low Media Loss value. If your sound spikes or drops out during the decay phase, try reducing Tension Mod, and perhaps Resolution.

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Sculpture string parameters in Logic Pro for iPad

String parameters