The U.S. Patent and Trademark Office officially published an important granted patent for Apple Inc. this week covering their HomePod device invention and specifically acoustic change direction.
Patent: (HomePod) Acoustic Change Direction
Apple's newly granted patent covers their invention relating to an audio system that automatically determines when to electronically adjust a digital audio rendering process, which is rendering an audio signal for conversion into sound by a loudspeaker cabinet, in response to automatically detecting a change in an acoustic environment of the loudspeaker cabinet. The patent relates to Apple's HomePod.
An embodiment of the invention is an audio system that adjusts how sound is produced through (by) a loudspeaker cabinet, when there are (or in response to) changes in an acoustic environment in which the loudspeaker cabinet resides. The audio system includes a loudspeaker cabinet that is configured to produce sound, a processor, several pairs of microphones, and a non-transitory machine readable medium (memory) in which instructions are stored which when executed by the processor automatically perform an acoustic environment change detection process.
Each "pair" of microphones includes a same (or shares the same) internal microphone that is configured to capture sound inside a speaker driver back volume of the loudspeaker cabinet, and a different external microphone that is configured to capture sound outside the loudspeaker cabinet (but that may still be integrated into the loudspeaker cabinet.)
The non-transitory machine readable medium stores instructions which when executed by the processor cause the system to, for each pair of microphones, receive (i) a first microphone signal of internal sound captured by the internal microphone and (ii) a second microphone signal of external sound captured by the different external microphone of the pair. The first and second microphone signals are used to estimate a radiation impedance of the loudspeaker cabinet.
A detection metric or radiation impedance metric (also referred to here as a detection value or a radiation impedance metric) is computed, based on the radiation impedance in a frequency band. A difference between (i) one of the "current" computed detection values associated with a given pair of microphones and (ii) a previously computed detection value associated with the given pair of microphones is computed. The process then adjusts how the audio system renders an audio signal that is to produce sound through the loudspeaker cabinet, in response to the computed difference meeting an acoustic change threshold.
In one embodiment, the acoustic change threshold is selected based on a determination of whether the loudspeaker cabinet has been moved. The loudspeaker cabinet can include (e.g., integrated therein) an inertia sensor (e.g., accelerometer, gyroscope, and magnetometer) that detects movement of the audio cabinet.
Once movement is detected, the acoustic change threshold may in response be lowered, which makes it more likely that the acoustic environment change detection process will detect a change in the acoustic environment. For instance, if the acoustic change threshold is lowered, then the required difference (between the current computed detection value and the previously computed detection value) decreases as well, thereby increasing likelihood that the audio system will adjust the rendered audio signal.
This may ensure that the audio system performs better or is better adapted to a possibly changed acoustic environment (e.g., where the loudspeaker cabinet is repositioned within the same room or is moved to a different room). The detection of movement, using data output from the inertia sensor, may also be used to bypass the performance of the acoustic environment change detection process. For example, upon a determination that the loudspeaker cabinet has moved beyond a motion threshold, the audio system may automatically adjust the rendered audio signal.
Apple's patent FIG. 1 shows an example cylindrical loudspeaker cabinet that includes a sound output transducer and six microphones.
Apple's granted patent 9,992,595 was originally filed in Q2 2017 and published on June 5, 2018 by the US Patent and Trademark Office.
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