Perception of Temporal Decay of Low-frequency Room Modes
Modal equalization has recently been of research interest in order to improve sound reproduction in rooms that have excessively strong modes at low frequencies. Instead of acoustic treatment by expensive and space-reserving absorbing structures, modal equalization is based on DSP affecting the electric-to-acoustic reproduction chain. Several DSP-based techniques for modal equalization have been proposed recently and tested in performance. From a perceptual point of view, however, no clear picture on the importance of controlled temporal decay has been shown, although it is known that towards the lowest frequencies the human hearing becomes increasingly insensitive to temporal details. In the present study we conducted listening tests where only a single synthetic mode with increased decay time but magnitude-equalized response was used to find the JND threshold of excessive decay time. The main conclusion is that at typical listening levels and down to 100 Hz the modal decay time T60 is allowed to increase from about 0.3 seconds by 0.1 to 0.4 seconds, while at 50 Hz even decay times of up to two seconds do not make a noticeable difference.
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