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Excitation Factoring

As another refinement, it is typically more efficient to implement the highest Q resonances of the soundboard and piano enclosure using actual digital filters (see §8.8). By factoring these out, the impulse response is shortened and thus the required excitable length is reduced. This provides a classical computation vs. memory trade-off which can be optimized as needed in a given implementation. For lack of a better name, let us refer to such a resonator bank as an ``equalizer'' since it can be conveniently implemented using parametric equalizer sections, one per high-Q resonance.

A possible placement of the comb filter and equalizer is shown in Fig.9.37. The resonator/eq/reverb/comb-filter block may include filtering for partially implementing the response of the soundboard and enclosure, equalization sections for piano color variations, reverberation, comb-filter(s) for flanging, chorus, and simulated hammer-strike echoes on the string. Multiple outputs having different spectral characteristics can be extracted at various points in the processing.
Figure 9.37: Example block diagram of a more complete commuted-piano synthesis system.

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