US Patent 9307340 Audio system equalization for portable media playback devices

A method, an apparatus, a system, and instructions stored in a non-transitory computer-readable medium to instruct a processing system to carry out the method. The method includes applying corrective filters directly in a portable media device to correct, e.g., equalize for the overall system comprising the portable media device and the playback system to which it is attached. Also a method of determining the corrective filters by playing back one or more calibration signals on the playback system while recording the resulting sound field on the portable media device.