The ``physically informed spectral additive modeling'' (PhISAM) technique is based on modal synthesis with the addition of ``physical'' parametric controls such as ``stick hardness'' and ``strike position''.
The approach is suitable for resonant percussion instruments characterized by impulsive excitation of a relatively few exponentially decaying, weakly coupled sinusoidal modes (i.e., marimba, vibraphone, cowbell, ...).
Frequency tracking, or mode ``picking'', can be accomplished using Fourier analysis, linear predictive coding, or other all-pole filtering techniques.
Prototype excitations can be determined by recording a stick strike while damping the resonant modes of an instrument or by extracting a residual signal from an LPC or sinusoidal analysis.
Physical parametric controls, such as strike position and stick hardness, can be simulated using simple rules to control modal gains.
The analysis/resynthesis approach can be outlined as:
Take a recorded sound and perform high-order LPC, ARMA, or SMS sinusoidal + noise analysis:
Determine the N highest-Q resonances or highest-amplitude FFT peaks;
Extract LPC residual or SMS noise envelope for resynthesis excitation or record a dry strike.
Derive resynthesis parametric control rules:
For strike position, analyze modal behavior for various strike position excitations;
For stick hardness and strike vigor, first choose resynthesis method (resonant filters or sinusoidal functions) and then derive rules.
Perform resynthesis with derived rules and include dynamics of player/performer.
A PhISAM system block diagram is shown in Fig. 8 below.
A PhISAM system block diagram.
The ``stick hardness'' can be simulated by varying the playback rate of the strike signal. That is, a softer strike can be simulated using a recording hard strike by reading through the sound at a slower rate. This effectively lowers the frequency content of the original sound.