What a diver hears with his own ears is actually only a tiny part of the sound that reverberates around the water. The sea is a veritable sonic reservoir.
The silence of the deep is very noisy – that has been confirmed by the first underwater listening.
Who remembers the film by Jacques-Yves Cousteau and Louis Malle that won the 1956 Palme d'Or at the Cannes Festival?
It is no doubt thanks to this film, and the fact that we have spent more than twenty years making re-recordings of films by Les Requins Associés (a whole set!) and then by the Cousteau Society, that we have become, among other things, specialists in underwater sound recording.
For Luc Besson's The Big Blue we supplied miniature hydrophones for stereophonic sound recording.
These mics were specially designed in the 1970s to detect Soviet November-class nuclear submarines, which used to like frequenting the Brittany coastline near Île Longue (Enez Hir in Breton).
The quality of these submarines was awful, as they made as much noise as a Gay Pride festival and were very unreliable. It was not for nothing that they were nicknamed widow-makers!
Sound travels four times faster in water than in air, at 1,500m per second compared to 340m per second. Hence the importance of keeping hydrophones at a distance of at least 70cm.
Pierre Befve won the César Award for Best Sound in 1989 for his work on this film, which became a cult classic thanks also to the character of Jacques Mayol, who was played by Jean-Marc Barr.
In addition, a few years ago we helped to record the clicking sound made by the sperm whale at 230dB underwater (a world record) at a frequency range between 0.1Hz to 30khz.
The ability to detect sound precisely amid this aquatic cacophony depends heavily on the level of ambient noise in the water. So, since the intensity of sound dwindles with distance, it will only be perceptible within a certain radius of the source.
Last September, a team of scientists of the Bigouden Institute of Pectinidae (B.I.P) asked us to make a prototype that would allow them to study the movement of scallops while being able to record sound.
We know that swimming is exhausting for this mollusk. It usually has to limit its movements because its huge muscle uses up a lot of energy if it moves too much, causing it to lose weight.
In order to listen to scallops without taxing our ears, we used MEMS, which stands for Micro-Electro-Mechanical-Systems.
These MEMS are generally mechanical devices with electronic elements.
Philippe Chenevez (Cinela), who had just come back from Santiago de Compostela and is a leading specialist in sound recording with MEMS, especially for CNAM, helped us to attach them to waterproof mini-recorders.
We were able to record the sounds emitted by scallops when they breathed and ventilated. Their breathing is intense, like the exhaling of the humpback whale.
Each movement of air within the scallop is accompanied by a long noise. These creatures are discreet but they talk and, like doctors with stethoscopes, we can pick up any abnormal sounds they make when they are not well and are moving in an unusual way.
So underwater life is deeply reliant on a certain tranquility.
The sounds of the submarine world are beautiful because sometimes they mean nothing. They are random and pointless.
* Thanks to Vincent Montrobert, sound designer, for the exclusivity of these few scallop sounds of the documentary The Scallop Way produced by Arte & Nature.
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What they think about
Olivier Le Vacon
Wednesday 01 April, 2020
Magnifique. Magnifique. Magnifique. ( Désolé de la répétition, mais 50 caractères minimum !!!! )