Acoustic Bandwidth Compression (ABC)

We have developed a real-time acoustic bandwidth compression algorithm that enables acoustic signals with large bandwidth to be compressed into a bandwidth that humans can hear. The application of this algorithm is to enhance the diver experience, by enabling him or her to appreciate the rich soundscape the underwater world has to offer. We have demonstrated that a stereo implementation of the algorithm enables the diver to localize the sound source. This further enhances the experience and may potentially improve dive safety.

Many animals and systems radiate ultrasound that contains valuable information, from bats to high-voltage power lines in land, to marine animals underwater. Owing to a request to listen to high-frequency dolphin sounds in real-time, ARL developed a real-time bandwidth compressor that can convey the prominent features of ultrasound into the human hearing band. The algorithm requires no assumption of where in the ultrasonic frequency band (except the maximum frequency) of interest nor when in the time domain the information is encoded.

Source Localization

Humans can tell the direction from which a sound originates to an amazing accuracy in air. However, sound localization by the human auditory system is known to be ineffective underwater. By combining the ABC algorithm with a pair of directional receivers, we can introduce Inter-aural Temporal Differences (ITD) and Inter-aural Intensity Differences (IID) cues to human divers. We are thus able to introduce a sense of direction into their hearing in water. The prototype system consists of a pair of directional receivers of less than 60 mm diameter that are spaced and angled in such a way that high frequency directional cues from 20 kHz - 200 kHz are created in the audio hearing range, providing a sense of direction. Several experiments have been conducted in a small tank to study the performance of the system. The preliminary results are very promising. Independent tests on the directional receivers show that subjects are able to differentiate direction to within ±12 degree 95% of the time. The subjects remarked that there was a clear sense of direction in their hearing tests.

Relevant Publications