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Reflecting on Reflections - June 2014
Quiet Thoughts on a Deafening Problem - May 2014
AES Journal Forum
Subjective Investigations of Inverse Filtering
Inverse filtering is the concept that one can "undo" the filtering caused by a system such as a loudspeaker or room. This approach strives to correct both the magnitude and the phase of the system. Inverse filtering has been proposed for numerous applications in audio and telecommunications, such as loud speaker equalization, virtual source creation, and room deconvolution. When inverting the impulse response (IR), undesired audible artifacts may be produced. The severity of these artifacts is affected by the characteristics of the IR of the system, and the method used to compute the inverse filter. When the IR is nonminimum phase, the artifacts tend to be more severe and become distinctly audible. The artifacts produced by the inverse-filtering process can actually degrade the overall signal quality rather than improve it. Formal subjective tests were conducted to investigate and highlight potential limitations associated with several inverse-filtering techniques. Time-domain and frequency-domain methods were implemented, along with several types of regularization and complex smoothing to help reduce the level of audible artifacts. The results of the subjective tests show that the various inverse-filtering techniques can sometimes improve the subjective quality and in other cases degrade the audio quality.
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