PM: Physical Modeling Synthesis
Physical Modeling Synthesis: Karplus Strong
Physical Modeling Synthesis: Karplus Strong Synthesis
Synthesizing Acoustic Sound
With PM we can create quasi acoustic sounds, such as a plucked guitar, string, flute or drum hit. But other than with samplers we can also tweak parameters (e.g. instrument body density, string length) in order to create specific types of instruments from a generic model. In the extremes, one can specify strange and unrealistic parameters in order to create models of instruments that are impossible to realize physically! Physical modeling systems typically use delay lines in their structure and this can mean that the output of the system can go out of control and create unwanted feedback..
Physical Modeling synthesis is not confined to a particular technique, but rather represents a variety of approaches to synthesis. Physical modeling attempts to model the propagation of sound energy, typically starting with a mathematical model that is often recursive. Physical modeling techniques also often start by attempting to replicate the basic structure of an acoustic instrument and therefore mimic the sound it makes when ‘excited’. This excitation normally comes in the form of an initial impulse, typically a short burst of noise.
Karplus-Strong synthesis is a simple wave-guide system using a short delay with feedback and filtering in the feedback loop. This simple setup is one of the basic building blocks of physical modeling synthesis that is aiming at recreating the resonant characteristics of real physical objects or acoustic instruments.
In Ableton we can recreate this best with the Echo effect doing this simple experiment:
- Create a very short burst of noise with with a sharp attack using Analog or also use a short percussive sound (e.g. a rimshot) in Simpler. .
- Set the Filter to a low-pass filter with a cutoff frequency around 1-2 kHz..
- Set the delay Time in Echo to a short value, such as ca 3-10 ms. Higher times will result in a delay effect.
- Carefully increase the feedback parameter to around 100% to create the sustained tonal feedback loop.
- Be careful with the feedback not to damage your speakers or ears!
- By notching the delay time up or down you will notice a change in pitch and if that delay time would by control by a keyboard ye would have a playable instrument.
- Adjust HP and LP settings in the Filter while slowly raising the Resonance as welt to shape the tone of the sound.
- By adjusting the Decay and Release parameters of an Amp envelope we can then further control the volume of the sound..
Experiment with different wave shapes, filter types, and delay settings to create a variety of sustained or plucked sounds using this simple waveguide setup.