For a further reduction in cost of implementation, particularly with respect to memory usage, it is possible to synthesize the excitation using a noise signal through a time-varying lowpass filter . The synthesis replaces the recorded soundbard/enclosure sound. It turns out that the sound produced by tapping on a piano soundboard sounds very similar to noise which is lowpass-filtered such that the filter bandwidth contracts over time. This approach is especially effective when applied only to the high-frequency residual excitation after factoring out all long-ringing modes as biquads.
Coupled Piano Strings