Removing Reflections in Semianechoic Impulse Responses by Frequency-Dependent Truncation

Acoustic reflections in impulse responses can be eliminated by truncation to short ("pseudoanechoic") observation times that exclude the reflections. However, truncating the response tail distorts the corresponding low-frequency transfer function. When reflections in "semianechoic" data originate from moderate-sized objects, e.g., equipment in anechoic chambers, their composition is high-pass. Consequently, truncation only must be performed in the mid-to-high frequencies where the information is contained in a brief time interval, while the impulse response tail is anechoic for the low frequencies and can be retained. We present a frequency-dependent truncation approach that exploits this observation by adaptation of the truncation length in each band, and therefore avoids low-frequency errors while disturbing reflections are windowed out. Among several tested formulations, a novel Short-Time Fourier Transform based formulation generated least artifacts while the anechoic impulse response was retrieved well from both simulated and measured semianechoic data.