Apple Invents a Stereo System with an Adaptive Room Equalization Feature
Today, the U.S. Patent and Trademark Office published a patent application from Apple that reveals a stereo speaker system that measures the impulse response of a listening area so as to provide listeners with exceptional quality audio depending on the room's configuration and the furniture within. It ensures the listener is delivered the 'sweet spot' of the audio every time. The sounds are sensed by a listening device (such as an iPhone or other device) proximate to a listener and transmitted to the loudspeaker. The loudspeaker includes an adaptive filter that estimates the impulse response of the listening area based on the signal segment. It's interesting to note that the Apple engineer that's listed as the sole inventor on this patent filing once worked for Bose Corporation.
Apple's Patent Background
Loudspeakers and loudspeaker systems (hereinafter "loudspeakers") allow for the reproduction of sound in a listening environment or area. For example, a set of loudspeakers may be placed in a listening area and driven by an audio source to emit sound at a listener situated at a location within the listening area. The construction of the listening area and the organization of objects (e.g., people and furniture) within the listening area create complex absorption/reflective properties for sound waves. As a result of these absorption/reflective properties, "sweet spots" are created within the listening area that provide an enhanced listening experience while leaving a poor listening experience for other areas of the listening area.
Audio systems have been developed that measure the impulse response of the listening area and adjust audio signals based on this determined impulse response to improve the experience of a listener at a particular location in the listening area. However, these systems rely on known test signals that must be played in a prescribed fashion. Accordingly, the determined impulse response of the listening area is difficult to obtain.
Apple's Invention: Adaptive Room Equalization using a Speaker and Handheld Device
Apple's invention relates to a loudspeaker system that measures the impulse response of a listening area. The loudspeaker may output sounds corresponding to a segment of an audio signal. The sounds are sensed by a handheld listening device proximate to a listener and transmitted to the loudspeaker. The loudspeaker includes a least mean square filter that generates a set of coefficients representing an estimate of the impulse response of the listening area based on the signal segment. An error unit analyzes the set of coefficients together with a sensed audio signal received from the handheld listening device to determine the accuracy of estimated impulse response of the listening area. New coefficients may be generated by the least mean square filter until a desired accuracy level for the impulse response is achieved (i.e., an error signal/value below a predefined level).
Apple notes that in one embodiment, sets of coefficients are continually computed for multiple input signal segments of the audio signal. The sets of coefficients may be analyzed to determine their spectrum coverage. Sets of coefficients that sufficiently cover a desired set of frequency bands may be combined to generate an estimate of the impulse response of the listening area relative to the location of the listener. This impulse response may be utilized to modify subsequent signal segments of the audio signal to compensate for effects/distortions caused by the listening area.
Apple's patent FIG. 1A illustrated below shows us a view of a listening area with an audio receiver, a loudspeaker, and a handheld listening device; FIG. 1B shows us a view of another listening area with an audio receiver, multiple loudspeakers, and a handheld listening device.
Apple's patent FIG. 5 shows us one of the methods for determining the impulse response of the listening area.
Apple patent application 20160029142 was filed in September 2015 with references dating back to 2013. Considering that this is a patent application, the timing of such a product to market is unknown at this time.
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