LISTENING UNDERWATER

SOUND AND HEARING :::

Sound is a physical phenomenon, produced when an object vibrates and generates a series of pressure waves that alternately compress and decompress the molecules of the air, water, or solid that the waves travel through.

These cycles of compression and rarefaction can be described in terms of their frequency, the number of wave cycles per second, expressed in Hertz.

Each sound we hear is composed of numerous sine wave components (partials), each at a different frequency. The higher a sound's frequency, the shorter the wavelength, the lower the frequency, the longer the wavelength. The lowest frequency is perceived by the ear as the pitch of the sound, and is called the fundamental. The other components are called harmonics. The relative amplitudes of each of the partials in a sound determine its timbre, or its most recognizable characteristic.

Our hearing is a coordinated effort between the ear and brain to gather information regarding our surroundings by collecting and analyzing these waveforms.

Because the brain has no sound receptors, the ear functions to convert sound vibrations to electro-chemical impulses that the brain then interprets as pitch, volume and timbre.

Of the many functions of the ear, an important one is to act as an early-warning device - alerting us to events that are happening around and behind us - things outside the jurisdiction of the eye. This was especially important in the ancestral village whereby you gained a distinct advantage if you could hear something before you spotted it - or it spotted you.

The human ear is limited to detecting frequencies between 20hz and 20khz.Certain whales, bats and other creatures have the ability to perceive frequencies much higher than the human spectrum.

Dogs and bats are examples of many creatures that can hear sounds at much higher frequencies--up to 160,000 Hertz. Much like radio waves, these creatures communicate in a spectrum which we cannot detect unaided. Because we compare their world of hearing to the constraints of ours we call these sounds ultrasound. Other animals, such as Sperm whales and elephants, use frequencies in the range of 15 to 35 Hertz (sounds that for the most part can't be heard by humans because the frequency is too low and are thus labeled infrasonic or subsonic).

Our hearing is also limited by our acoustic timing or sampling rate. Loosely defined, this is the amount of information we can perceive in a given time. For example: one Chickadee's song might not seem that different from another Chickadee's song to our ears because our sampling rate is too slow to detect the minute fluctuations in pitch and rhythm between one bird's call and the next. Slow the call down and these nuances become apparent.

The first audio file is a sample of an Orca call played in real time. The second audio file is the same call pitch and time shifted to three times its original length. The third is the first call sped up twice. Subtleties that aren't apparent in the first recording become noticeable in the second. Likewise, the third call erases many of the nuances of the original call - yet reveals other qualities.

A third factor in our ability to hear is the position of our ears. Our ears occupy opposite sides of our head which causes sound signals from various directions to reach our ears at different times.

The brain registers the delay in signal from one ear to the other and extrapolates the location of the sound to a greater or lesser degree of accuracy. If our ears were as far apart as an elephants we would be able to localize with a much higher degree of accuracy as would be true if we could turn and focus our ears as a dog or cat is able to do.

Humans are not only able to perceive sound, but are also skilled at creating and controlling sound. These abilities have led to complex acoustic systems that have significantly enabled our survival and dominance in the food chain.

At some point back in our ancestral village, we realized the benefits of combining our efforts in a group - such as for hunting or war. With the complicated teamwork required for these activities arose the need to communicate in precise and logical terms.

While a grunt and a head nod might suffice for directions to a watering hole, instructions for building a well required more explanation.
In response to these needs we created a system that depended as much on our vocal cord flexibility as it did on our mental abilities. Spoken language incorporated a much higher level of symbolism than grrr for bear and bzzzz for bee by developing a complex code of relationships between sound, objects and concepts - allowing us to communicate with precision and describe with accuracy.

With the advent of language the exchange of information rapidly increased. Before the invention of writing, oral histories contained all the important details of instruction, history and genealogy and grew more complex as time progressed.

One trick to memorizing the many details may have been the use of rhyme: the correspondence in terminal sounds in a verse. Rhyme creates a rhythmic pulse and imparts on words a mnemonic quality - whether in rap songs or lullabies.

For example:
"Twinkle twinkle little star, how I wonder what you are"
is much more memorable than
"There's a star in the sky. It's twinkling. What is it?"

Rhythm's importance cannot be underestimated as it is a crucial factor in most of our abilities - whether walking, running or chopping wood.

These activities take place in response to internal rhythmic cues - possibly heartbeat, breath rate, or even rate of chemical breakdown. To complete a task beyond our individual strength - such as pulling a log or carrying a load - requires group participation. At some point in our history we realized by providing an external rhythmic pulse, such as banging on a drum or hitting rocks together we could greatly increase our efficiency by creating synchronized movement.

At some point in our development, we combined elements of rhythm and pitch with language and poetry and began to create music.

We also began to create complementary systems that enhanced our acoustic communication through the creation of symbols that represented sound, such as written language and musical notation. These systems greatly improve upon our innate acoustic memory and allowed for vast amounts of information to be documented and transmitted without any loss of integrity over distance or time.

Underwater Sound :::

The speed of sound in water travels approximately five times as fast in water as in air at 1,435 meters (or 1,569 yards) per second.

Traveling through the sea, an underwater sound signal becomes delayed, distorted and weakened, reflecting on boundaries of underside surface of waves, bottom and shores, bubbles, suspended particles and marine life.

Tide, current, temperature variances and wind also play on a sound's final quality.

The ocean is not a silent place and its natural ambiance ebbs and flows. Variances can be seasonal, such as the presence of a storm track that introduces loud wave noise, or hourly, such as the dropping of the tide. Other sounds can be constant as snapping shrimp or sporadic as earthquakes.

In 1943, researchers discovered the presence of "sound pipelines" along the ocean's floor which allow sounds to travel over 2,000 miles with minimal loss of signal - allowing freighters leaving San Francisco Bay to be recorded off the island of Japan. Called the sound fixing and ranging, or SOFAR channel, these pipelines are also known as the "deep sound channel".

Sound traveling in an underwater pipeline between New York and London - a distance of 3471 miles (5585 km) would take approx. 1hr. To fly this distance takes approx. 4 hours.

Cetacean Adaptation :::
Centuries ago, certain land mammals left their terrestrial existence and returned to the water. This transition took place over a great length of time and cause substantial morphological changes to the descendants, known collectively as cetaceans (marine mammals). These mammals retained many of the sensory organs associated with land-based animals: eyes, ears, nose (blowhole) which adapted to the aqueous environment by developing new levels of efficiency.
The blowhole became positioned on the top of the head, allowing for exhalation when surfacing. The lungs increased in capacity and adjusted to functioning under tremendous pressures. The eye protected itself from the sea's salinity by producing a thick membrane as did the ear's openings. The eye, however, could not adapt to the near-constant darkness of the ocean and it is here we see a shift to reliance on sound and the ear.

Before the advent of navigational aids such as compasses and GPS systems, seafarers used a technique of detecting land during times of low visibility by shouting out into fog and listening for a returning echo. Much later mariners would be using a more developed technique to judge the ocean's depth and contents with the use of sonar (sound navigation ranging). At the basis of sonar is a ping! sent out from the transmitter with the delay of its returning echo measured and interpreted as size, density and distance. Though much more organic in nature, the Orca (Killer Whale) emits a high-frequency click of their own known as echolocation which provide the Orca with a "view" of the surroundings and aids in both navigation and hunting.

This view does not present the world as we see it through our eyes. An Orca "listening to" another Orca more aptly "listens through" the other creature - hearing the body contours diffusely, teeth and bone somewhat better, and those parts containing air (alimentary canal, breathing passages and air cavities in the skull) quite distinctly.

This intimate view of one another may have an impact on the structure of Orca society which consists of a weave of clans in varying degrees of kinship to each other. Mothers and female offspring remain together for life in a community known as a pod, each of which features a unique vocalization, or dialect, that is passed on through the generations. By clicking on each of the pictures above, you can get a sense of the different dialects.

Humpback whales provide an interesting study as they vocalize mainly within the range of human hearing. Humpback society is not organized in pods or any other kinship-based system. However the whales do form temporary coalitions during the feeding ritual known as lunge or group feeding in which up to 15 whales encircle a ball of herring in a bubblenet and then blast out a feeding call before lunging to the surface.

Although one tends to focus on the swoops and cadences of the call, it is also very pulsing and rhythmic in nature.

Another type of Humpback vocalization is heard in the breeding season.Floating upside-down, the Winter Song comprises a wide-sweeping range of low grunts to high whistles and is sung in a continuous cycle by the males.

The 20 - 25 minute song begins each year where it left off the previous year and introduces new elements as the season progresses, bringing up comparisons with the human tradition of oral historiesResearchers such as Drs. Katy and Roger Payne have noted a strong semblance between the phrases and rhymes found in the Winter Song and the patterns found in poetry.

To help identify these poetic elements, the spectrum analysis above shows repeating elements of a small section of the Winter Song labeled 1 through 4. When you click on the image, try to follow the divisions as the whales repeat the trumpeting and low grunts.

This second snippet is much more complex and has been divided into two main sections: 1 and 2. Each section has been further subdivided by letters a through e. Click on the image to hear the song and while listening, try and follow the bars on the frequency chart. a, b, and c correspond to the lower grunts (c being the strongest) with d and e the high frequency sweeps.

To further investigate these sounds and the possibilities they hold for crossing the species boundary, please visit the Interspecies Communication section