Projects/ 4-channel UDDAS/ How to record - part 1

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Challenges to recording dolphin sounds

To better understand wild dolphin behavior and ecology, an important first step is is to accurately record and analyze the sounds they produce.  However, this has proven very difficult in the past.  One of the main challenges to recording dolphin sounds accurately is the high frequencies that are present in dolphin sounds, i.e. up to more than 200 kHz.  Since conventional audio recording systems only record up to about 20 kHz (which is also the upper limit of human hearing), these systems would miss the majority of energy of dolphin signals.

Besides the high frequency content of dolphin sounds, another major problem is that it is usually impossible to tell which, or how many dolphins produced the recorded sounds.  This information is essential, however, to associate specific features of the sounds with behaviors of individual dolphins, or to find out how communication signals are exchanged among them.

Finally, the distance of the sound producing dolphin – which is needed to determine the amplitude of the recorded sound at the source – is usually unknown, as well as the orientation of its head with respect to the recording device.  The reason it is important to know head orientation is because dolphins emit sounds from their foreheads in a directional “beam” of sound, somewhat comparable to the light on a miner’s helmet.  Only recordings from the central beam axis represent the actual signals, while signals that are recorded off-axis can be highly distorted.  Since recording systems are usually operated from boats, it is hard to control for any of these factors.  Only by aiming the recording device underwater at the forehead of the sound producing dolphin, would it be possible to obtain accurate recordings reliably.

NEXT: How the 4-channel UDDAS addresses these challenges