This paper introduces a new signal processing system which enhances reverberance imagery (i.e. perceived ambiance or listener envelopment) in loudspeaker audio scenes. Sound components which affect reverberance imagery are extracted from a pair of unencoded audio signals and are radiated with two additional loudspeakers behind the listener. The new “ambiance extraction” system improves upon all extant systems by using a novel automatic (blind) equalizer based on the normalized least means square (NLMS) algorithm to align the input signals with respect to both level and time in order to create the difference signal. The alignment is typically undertaken using a 1024-tap frequency and ±10 ms time equalizer, which allows sound components with a high short-term correlation to be removed from the input audio signals. Subjective and objective evaluation was undertaken with recordings of solo musical performances in a concert hall, and show that the new system provides a computationally practical, high-quality solution to the problem of ambiance extraction for audio upmixing.
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