Empirical Notes on Inverse Filtering Experiments

In experiments factoring guitar body impulse responses, it was found that the largest benefit per section comes from pulling out the main Helmholtz air resonance. Doing just this shortens the impulse response (excitation table) by a very large factor, and because the remaining impulse response is noise-like, it can be truncated more aggressively without introducing artifacts.

It also appears that the bandwidth estimate is not very critical in this case. If it is too large, or if ``isolation zeros'' are not installed behind the poles, as shown in Figs. S.6b and S.9b, the inverse filtering serves partially as a preemphasis which tends to flatten the guitar body frequency response overall or cause it to rise with frequency. This has a good effect on the signal-to-quantization-noise ratio versus frequency. To maximize the worst-case signal-to-quantization-noise versus frequency, the residual spectrum should be flat since the quantization noise spectrum is normally close to flat. A preemphasis filter for flattening the overall spectrum is commonly used in speech analysis [372,301]. A better preemphasis in this context is an inverse equal-loudness preemphasis, taking the inverse of an