Room Impulse Response Shortening by Channel Shortening Concepts

Abstract

This paper addresses the usability of channel shortening equalizers known from data transmission systems for the equalization of acoustic systems. In multicarrier systems, equalization filters are used to shorten the channel's effective length to the size of a cyclic prefix or the guard interval. In most data-transmission applications, the equalizer succeeds the channel. In acoustic systems, an equalizer is placed in front of a playback loudspeaker to generate a desired impulse response for the concatenation of the equalizer, a loudspeaker, a room impulse response, and a reference microphone. In this paper, we modify the channel shortening paradigm and show that shaping the desired impulse response to a shorter reverberation time is more appropriate for acoustical systems than exactly truncating it.

Optimized gradient calculation for room impulse response reshaping algorithm based on p-norm optimization

“…The task of filter reshaping is to design h(n) in such a way, that g(n) contains no audible echoes. Here, we follow [2,3] and define a desired and unwanted part of the global RIR using two windows w d (n) and wu(n) as g d (n) = g(n) · w d (n) and gu(n) = g(n) · wu(n) respectively. As proposed in [3], we use…”

“…As proposed in [2,3] it is sufficient to shape the overall RIR with respect to the human auditory system. Therefore, for reducing the reverberation, it is sufficient to equalize the RIR in a such way that the audible echoes are removed, while the inaudible ones may stay unaffected.…”

“…The methods for prefilter design in [2,3] are gradient-descent approaches, which minimize either an Euclidean norm, an p-norm, the ∞-norm or a combination of them. These norms are necessary, as the least-squares methods based on the 2-norm do not allow for a precise control of the very small coefficients in the tail of the reshaped RIR.…”

“…In order to reduce the influence of the reverberation in acoustic scenes and to improve the perceived quality the concepts of room impulse response (RIR) shortening and reshaping have been introduced [1,2,3]. Using a filter to either preprocess the loudspeaker signal or postprocess the recorded microphone signal, the overall impulse response is equalized [4].…”

Speech reinforcement in noisy reverberant environments using a perceptual distortion measure

“…Traditional approaches [11] use a deterministic inverse pre-filter, being inherently unrobust with respect to displacement of the listener. More recent approaches concentrate on shortening ("reshaping") the global impulse response, by maximizing an p -norm based objective corresponding to a desired response segment [12,13].…”