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Control rooms designers typically measure and specify rooms according to their physical structure and acoustic properties. They are unable, however, to measure or predict how well the room will support the subjective qualities of stereo imagery produced over loudspeakers. As the quality and salience of stereo imagery improve through the use of more sophisticated recording and processing techniques, control room requirements become more stringent. Beyond speaker placement, there are three primary factors that influence the perception of stereo images: time-energy-frequency characteristics of the speakers, spatio-temporal distribution of early reflections, and the inclusion of acoustic diffraction. These are easily measured through the use of time delay spectrometry (TDS), but at present an adequate model for predicting subjective response from these physical measurements is lacking. Ensuring the perception of optimal stereo imagery requires the application of standardized subjective evaluation techniques. Currently under development at Northwestern Computer Music (NCM) is an evaluation technique using the Listening Environment Diagnostic Recording (LEDR™), which enables the immediate assessment of changes in stereo imagery that result from progressive changes in control room acoustical treatment. Field tests indicate that LEDR™ is valuable in the design and modification of control rooms for optimizing stereo imagery. [ABSTRACT FROM AUTHOR]

A spatial sound processor for stereo headphone and loudspeaker reproduction is described that can position sound elements within a three-dimensional reverberant space surrounding the listener. Spatial motion of sound sources in three dimensions is created by dynamic filtering based on head-related transfer functions. Additional filters and delay lines capture air absorption and Doppler shifting as the propagation time is manipulated for both direct and indirect sound. The spatiotemporal distribution of early reflections is captured for a given source/listener orientation: The gain, delay, and directional filtering of simulated reflections are responsive to changes in the specified position and orientation of the sound source and the listener's head in the simulated environment. The spatial processor can be used for headphone reproduction using a head-tracking device, and can also be used in more typical reproduction settings such as living rooms with stereo loudspeakers. In the latter case, additional processing is employed to stabilize the stereo image and produce a spatially diffuse reverberant surround effect over a wide range of listening positions. [ABSTRACT FROM AUTHOR]