Blue Planet II
The award winning BBC nature documentary B l u e P l a n e t II (2017) reveals breathtaking stories of the underwater world. Amongst other new recording techniques, some specially developed for the series, Ambient’s underwater surround system helped them to unlock a not so silent world.
Unlike the physics of airborne acoustics, sound waves in water travel 4.5 to 5 times faster than they do in the air. That also leads to an equivalent greater wavelength and allows blue whales to communicate over thousands of kilometers. But the language of marine animals still seems to be a mystery.
Dr. Steve Simpson is marine biologist and expert on fish bioacoustics from the University of Exceter, and was supervising the BBC crew on its expeditions. He knows how important sound is for marine life. “I have been working on coral reef acoustics for about 17 years now. We are finding fish and many other invertebrates listen to their habitat to select where they live. That sound is generally biological.”
“More recently, we are trying to understand why animals are making all this sound and we realised the complexity of communication. We have been trying to unlock the language of fish in context of reproduction, competition and predation, interspecific communication as well as within species. So there is a growing understanding of the importance of the underwater acoustic world for animals that live in it.”
Recording the underwater soundscape
In order to make the series sound more naturally realistic – for example by recording the underwater soundscape of a coral reef – the BBC producers went for the RS5 surround rig, including 4 directivity spheres maintaining low noise ASF-1 hydrophones. The multichannel array ran into a Sound Devices 788T embedded into a hard-anodized and PTFE coated underwater housing, specially built for the Sound Devices 7 series.
“We tend to use omnidirectional hydrophones which are great for capturing a soundscape but useless for identifying different sources of sound. We could also use accelerometer that measure particle motion which allows us to be able to discriminate direction of sound.”
“The system we were then filming with allowed us to be able to find differences in that soundscape. It gives that slightly more immersive flavour to the viewer. But I didn’t realise how also scientifically interesting it would be until we used the equipment. Conceptually it was genius.”
“Some of the recordings we made with the rig, but we also went to some of the reefs and just pulled out 30m of hydrophone cable in each direction from a central barrel with the recorder in it. That allowed us to be able to listen 60m apart. When you start listening over different distances, you obviously get to a point where you are losing overlap. As you come nearer, you start to get the overlap but you get real differences in intensities or in time of arrival. And as you get closer and closer they line up. Depending on the question, we find that we have been using hydrophones separated over different distances.”
Although most people are aware of the well known click detection of dolphins or the vocal sound of a whale, there is still a huge lack of knowledge in public about species using acoustic communication and in particular the importance of it for marine life.
For the “coral reef” episode, a small, rather inconspicuous fish attracts the attention of the B l u e P l a n e t II crew: the clownfish. By emitting a buzzing sound, the dominant female will warn off potential attackers and predators from their nest.
“Impact of human noises”
But by recording these underwater sounds, Steve and the crew were not only trying to put focus on biological sound sources. Noisy boats, seismic air guns used for oil exploration, sonar systems… just to short list some of the noise polluters around the sea. The damage to specific ecosystems is immense.
“In the UK and now more globally there is a growing concern of the impact of human noises in the ocean. Noises, which we know cause stress, affect distraction and can affect prey-predator dynamics as well as just masking communication. It is important to develop better ways either of us making the noise or technology that produces less noise. We can choose where and when we make noise, we can temporarily manage sound output and we can innovate new technology to reduce human noise.”
The B l u e P l a n e t II crew really pushed the boundaries of what’s technically possible and their spectacular recordings helped us to understand a little more about the most important ecosystem on Earth.
Ambient is proud of being involved, and to contribute voices to stories that haven’t been heard before.