Understanding the location of acoustically reflective surfaces in a room is a critical component in advanced sound processing. For example, intelligent speakers can use a room's acoustic geometry to improve playback quality, source separation accuracy, and speech recognition. In this paper, we present Synesthesia, a system for capturing the acoustic properties of a room using a single fixed speaker and a mobile phone that records audio at multiple locations. Using the arrival time of echoes, the system is able to reconstruct the position of reflective surfaces like walls and then estimate properties like surface absorption.

The proliferation of Bluetooth Low-Energy (BLE) chipsets on mobile devices has lead to a wide variety of user-installable tags and beacons designed for location-aware applications. In this paper, we present the Acoustic Location Processing System (ALPS), a platform that augments BLE transmitters with ultrasound in a manner that improves ranging accuracy and can help users configure indoor localization systems with minimal effort. A user places three or more beacons in an environment and then walks through a calibration sequence with their mobile device where they touch key points in the environment like the floor and the corners of the room. This process automatically computes the room geometry as well as the precise beacon locations without needing auxiliary measurements. Once configured, the system can track a user's location referenced to a map.

We demonstrate the Acoustic Location Processing System (ALPS), a platform that augments BLE proximity beacons with ultrasonic transmitters in a manner that allows for precise and robust indoor localization. {\em ALPS} uses Time-Difference-Of-Arrival (TDOA) and Time-Of-Flight (TOF) ranging to accurately localize mobile devices such as off-the-shelf smartphones and tablets in 2D space. Users inside the demo area will be able to determine their location and can directly plot it relatively to a map of the area using our app on a smartphone. Once a receiving device has determined its initial position, it can synchronize its audio clock with the transmission infrastructure to perform TOF-based localization, which provides similar position accuracy to TDOA based localization with fewer beacons. Multilateration and trilateration processing for each device's location is offloaded onto a cloud-based solver that can provide localization as a service to ALPS and similar TOF/TDOA based systems.