Category Sound

RECORDING

 To record sound, the pattern of vibrations in the air must be turned into a form that can be stored. The gramophone was the first sound-recording device. To record, the sound was made to vibrate a needle, which cut a wavy groove in a foil surface. To play back, the needle moved along the groove, making a diaphragm vibrate to reproduce the sound. In the electric gramophone, introduced in the 1920s, the vibrating needle created an electrical signal, which was amplified to drive a loudspeaker.

The first type of gramophone was the phonograph, invented in 1877 by the American inventor Thomas Edison.

Tape recording was developed in the 1940s. To record on to tape, the electrical signal from a microphone is sent to an electromagnet, which creates a pattern in the tiny magnetic particles that coat the tape. This pattern recreates the signal as the tape plays, and the signal is amplified before going to a speaker.

Most sound recording is now done digitally. A microphone turns the sound into an analogue electrical signal, which is then digitized more than 44,000 times a second to create a long string of binary numbers. The binary numbers can be stored in a computer’s memory or disc drives, or on a compact disc (CD). On a CD, the binary digits 0 and 1 are represented by flat areas or shallow pits in the surface. In a CD player, these are detected by a laser as the disc spins and reflected to a light-sensitive device. Electronics rebuild the original electric signal, which is amplified and sent to speakers. Computer CD-ROMs and DVDs work in the same way.

          Like treble, bass too describes a range of sound in terms of tone quality as well as musical notes. But they are opposite voices.

          Bass defines tones of low frequency, pitch and range from 16-256 Hz. Hence, it forms the lowest part of the harmony in songs. If we increase the bass up in a note, we get a deeper sound. On the other hand, if we volume up a treble, we get a higher sound.

          In choral music, bass is provided by adult male bass singers, while in an orchestra, the lines are played by the double bass and cellos, bassoon or contrabassoon, low bass such as the tuba and bass trombone, and the timpani or kettledrums. In popular music, the bass part or the ‘bassline’ provides a rhythmic support to the band.

           The main bass instruments used by musicians are keyboard bass and bass drum. 

            We know that all objects in the Universe have their natural frequencies. Some may be simple but some, complex. A renowned example for an object with a simple natural frequency is the tuning fork. It is an acoustic resonator that appears as a two-pronged fork with the prongs or tines formed from a U-shaped bar of elastic metal like steel. Depending on the length and mass of the two prongs, the fork produces a pitch. Generally, it is used as a standard of pitch to tune musical instruments.

            As mentioned earlier, a tuning fork has a natural frequency. When set vibrating by striking against a surface, or by an object, the fork resonates at a specific pitch and emits a musical tone once the high overtones have died out.

            Traditionally, the forks have been used to tune musical instruments. But today, electronic tuners are replacing them in applications.

            The tuning fork was invented in 1711 by British musician John Shore, who was a trumpeter and lute player. 

           Synthesizers are one of the most important musical instruments today. Although they look like small electronic pianos, the uses of synthesizers are much more than one can imagine.

           Technically, it is an electronic keyboard that can generate or copy, any kind of sound. For instance, it can mimic the sound of a traditional instrument like a violin or piano, or create brand new sounds like the crunch of footsteps on the surface of Mars!

           The very meaning of ‘synthesize’ is to make something new, often by putting together things from existing pieces. This is exactly what the synthesizer instrument does. It has got a number of oscillators or sound tone generators, each of which can produce waves of different shapes. They combine the waves to make complex sounds. Depending on this combination, the sounds vary, and mimic existing instruments.

             Based on how they function, synthesizers are classified into analogue and digital.

             The changes caused by synthesizers in the field of music are unparalleled. Since the 1970s, they have been used in popular music, and today, there is no pop record made without featuring an electronic keyboard of this kind. 

Mixing console is a device that used for mixing and changing the volume, and dynamics of audio signals. The sources of these signals could be many- microphones used by singers, or mics picking up the beats from drums.

The device is known by different names like audio mixer, audio console, or mixer.

There are numerous applications for which a mixing console is used. For instance, it is commonly used in recording studios, public address systems, sound reinforcement systems, musical concerts, broadcasting, television, and film post-production.

Let’s look at a few of its applications in detail. When two singers are singing, say a duet, a mixing console combines signals from the two microphones into an amplifier that drives one set of speakers. Then, during a live performance, the signals from the mixer go directly to an amplifier plugged into speaker cabinets.

Almost all bands use a mixer to combine musical instruments and vocals. This mix can then be amplified through a public address system.

Radio broadcasts too use it in order to select audio from different sources like CD players, and in-studio live bands. 

          The telephone is a communication tool that has become an integral part of human life since its invention in 1876.

          Technically, it is a device that transmits voices over a distance, using a wire or radio. The transmission is made possible by converting sound signals to electric signals.

          There are many reasons why the device is important to us. The first and foremost reason is that it enables communication without the hassle of travelling far.

             It is perhaps the cheapest mode of communication that facilitates talking to a person abroad at a relatively fair price. Hence, the device has played a major role in better socialization and interaction among people.

            Although it was originally meant for voice communication, telephones have evolved over the years. From wired phones emerged mobile phones that could be used anywhere.

             The telephone that we see around today was certainly not the first model developed for communication. Prior to its invention, many people had attempted to make different types of phones. However, Graham Bell’s telephone, invented in 1876 was the most successful.

             Most of the earliest models were mechanical acoustic devices that transmitted speech over a distance greater than that of normal speech.

             One important discovery during the 17th century was by Robert Hooke. He made an acoustic string phone in 1667. By the 19th century, various types of telegraphs were developed. It was after improvements of the electrical telegraph that the telephone emerged.

             There were many people who worked on this invention. However, it was Alexander Graham Bell, who won the patent for the device. 

          Sound recording and reproduction refers to the inscription and re-creation of sound waves, such as spoken voice, singing, instrumental music, or sound effects.

          The inscription could be electrical, mechanical, electronic or digital in nature. The earliest method of music reproduction was done through mechanical systems.

          Today, there are two main classes of sound recording technology – analogue recording and digital recording.

               Acoustic analogue recording is done with the help of a microphone diaphragm that can detect and sense the changes in atmospheric pressure caused by acoustic sound waves. It then records the waves as a mechanical representation on a medium such as a phonograph record.

              In digital recordings, analogue signals picked by a microphone are converted to a digital form by a process called digitization.

              The first all-digitally-recorded popular music album, Ry Cooder’s ‘Bop till You Drop’ was released in 1979. 

            The phonautograph was perhaps the first device in history that could record sounds. It was patented by French inventor Edouard-Leon Scott de Martinville in 1857.

            Phonautograms or phonautograph recordings made in 1857 were the earliest known recordings of the human voice. They consisted of sheets of paper with sound-wave-modulated white lines created by a vibrating stylus that cut through a coating of soot as the paper passed under it. That means the recordings were visual representations of the sound.

           The earliest known recording of intelligible spoken words is the phonautogram containing the opening lines of Torquato Tasso’s pastoral drama ‘Aminta’. It is believed to have been recorded in April or May, 1860.

           Luckily, a few recordings have been recovered over the past few years. The phonautogram of Au Clair de la Lune, a French folk song made in 1860 was played as sound for the first time in 2008. 

            The human ear is a wonderful organ that performs some of the most important functions in the body. It detects and analyzes sounds, and also maintains the sense of balance.

            Structurally, the external ear is created in a peculiar way. It has many twists and folds that help in enhancing certain sounds up to 100 times.

            Designed in a way as to make the skin maintain its funnel shape, a healthy ear enables the capturing of even the tiniest vibration.

            In addition, the ear can help determine sound direction. It can also decide the range of sounds we hear. However, as we grow old, we become less sensitive to sounds, and may not be able to hear high pitched sounds like the squeaking of a bat. But this could be picked up by a child. It has been found that a normal human can detect frequencies between 20 Hz and 20 kHz. 

                The concept of echo must be familiar to most of us. While standing in an empty space, if you let out a loud shout, you can hear a faint sound coming back after a few seconds. This reflected wave of sound that resembles the original is called the echo. It can be experienced when you are standing on top of mountains, in remote places, in big and empty rooms, in caves etc.

                The term echo is derived from the Greek word meaning sound. There are many factors influencing the creation of echoes. Typically, the sound waves can bounce off only if the objects they hit are smooth and hard. It is like a rubber ball bouncing off the ground. If the waves meet a soft surface, for example a cushion, they will be absorbed, and hence, no echo will be created.

                         There are multiple uses for echoes. They can be used to measure distance, velocity, and the shape of objects. It is to be noted that an improper arrangement of echoes will result in unclear sounds.

            The contributions made by the Ancient Greeks to the world of acoustics are unparalleled.

            One of them is the amphitheatre of Epidaurus, designed by Polykleitos the Younger, around the 4th century BC. The theatre had a tripartite structure, that is, an orchestra, auditorium, and stage building. There were also 34 rows of limestone seats that could accommodate 14,000 people.

            The acoustics of the place was such that a performer standing on the open-air stage could be heard in the back rows, almost 60 metres away.

            Experts attribute this rare feature to the arrangement of seats. According to them, the stepped row of seat structure was perfectly shaped so as to act as an acoustic filter. The seats suppressed low-frequency sounds that formed the major component background noise like the murmur of a crowd. This in turn, reflected high-frequency noises of the performers off the seats, and back toward the seated audience.

            We have read that most humans can hear sounds between 20 and 20,000 hertz. Ultrasounds are those above this limit or specifically, above 20,000 hertz. They are not different from the normal sound in terms of physical properties. But the only difference is that they can be heard and produced by only a few animals like bats, moths, dolphins etc. and not by humans. In other words, the range of ultrasound begins where our sonic range ends.

            The uses of ultrasound can be seen in electronic, navigational, industrial, medicinal and security applications. Let’s look at a few examples in brief.

            In some cases, ultrasound is used to detect objects or to measure distances. They are also helpful in testing products and structures.

            In addition to these, ultrasound is used in the field of medicine to view the internal organs of our body.

            There are quite a lot of animals that make use of ultrasound for purposes like navigation, communication, catching preys, avoiding obstacles etc. Let’s look at a few examples.

            Marine animals like dolphins and toothed whales are very famous for their sonar, which employs sounds from 250 Hz to 220 kHz.

            Then, there are the bats that have a variety of ultrasonic ranging techniques. They enable the mammals to detect preys and avoid obstacles, even in thick darkness.

            There are also many insects that have excellent ultrasonic hearing abilities. For example, like moths, beetles, lacewings, praying mantis etc. They use their skill to listen to echo locating bats. Upon hearing a bat, they make plans to escape being caught.

            Another group of animals that are responsive to ultrasonic sounds is mice. The next in the category of animals that can perceive high frequencies are dogs and cats.

             Sonar is the short form for Sound Navigation and Ranging. It is an ultrasonic system used in ships and other vessels for navigation, and locating objects underwater.

            As we know, sound waves travel faster than light through water. However, ordinary sound waves cannot travel longer distances, only ultrasonic waves can. Due to their high frequency and short wavelength, ultrasonic waves penetrate water to very long distances and it is this feature that is utilized in sonar.

            Let’s see how this works, in the case of a submarine. While deep in water, the vessel finds its way by sending out pulses of ultrasound and listening to the echoes. It is just like the phenomenon of echolocation in bats. Depending on the time it takes for the echoes to come back, the navigator of the vessel can figure out if there are any ships, submarines, or other obstacles nearby.

            This technique is also used by ships to calculate how deep the waters are by firing sound beams straight downward.

           The importance of ears is something we are all aware of. This organ is the receiver of sound in the human body and plays a very important role in communication.

           Structurally, the ear is made of three sections- the outer ear, the middle ear, and the inner ear. The outer ear is the visible external part which consists of the pinna and the ear canal. It gathers sounds and sends them to the middle ear through the ear canal.

           The middle ear is an air-filled cavity that turns sound waves into vibrations. It is separated from the external ear by the eardrum, a thin, cone-shaped piece of tissue. Past this drum, there are three small, but important bones in the middle ear. Collectively known as the ossicles, they are the malleus, incus and stapes.

           The third and final part of the ear is the inner ear. It consists of a tiny organ called the cochlea that converts the vibrations from the middle ear to nerve impulses. These impulses then travel to the brain, from where it gets converted as sound.  

            We already saw how our ears collect sounds from outside and conduct it to the inner parts. The sound waves are at first collected by the outer ear and passed through the ear canal. It then causes the eardrum to vibrate. Subsequently, these vibrations are transmitted to the cochlea by the tiny bones of the middle ear.

             Cochlea is a snail-shaped structure filled with fluid situated in the inner ear. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.

              Once the vibrations cause the fluid inside the cochlea to ripple, a travelling wave forms along the basilar membrane. Hair cells sitting on top of the basilar membrane ride the wave. The movement of hair cells eventually results in the formation of electrical signals.

              The auditory nerve carries this electrical signal to the brain, which turns it into a sound that we understand.

            A treble is a tone whose frequency or range is at the higher end of human hearing. In terms of music, it refers to ‘high notes’ or is the highest part in a composition that has three parts.

            The best examples of treble sounds are the tones of guitars, piccolos etc. Both of them are important instruments. They mostly have very high pitched sounds. The frequencies range from 2.048 kHz – 16.384 kHz.

            A treble clef or a G clef is used to notate such high sounding instruments like the violin, guitar, mandolin, flute, oboe, English horn, clarinet, saxophone, horn, and trumpet.

            In sound production, treble control is used to change the volume of treble notes relative to those of the middle and bass frequency ranges.

            An amplifier is a device used to increase or strengthen the power of a signal. They can be seen in audio equipment of all kinds.

            Let’s take the example of a hearing aid. It has a microphone that picks up sounds from all around and converts them to electric signals that constantly changes in strength. Here, an amplifier takes the signals, and boosts it many times before feeding it into the tiny loudspeaker placed inside the ear canal. The sound thus produced is ‘amplified’ before it reaches the person. That means, the duty of the amplifier is to convert a small electric current into a larger one.

            Depending on their functions, amplifiers can be categorized as weak-signal amplifiers or power amplifiers. The former is designed to deal with exceedingly small input signals. They are used in audio tape players, CD players tec. History notes that the first electronic device that could amplify was the triode vacuum tube, invented by Lee De Forest in 1906.

            Loudspeakers are equipments that we all are familiar with it. By definition, a loudspeaker is a tool that converts an electrical signal into sound waves to provide the most faithful reproduction that is feasible for its design. The most widely used type of loudspeaker is the dynamic speaker. The moving coil principle commonly used today in speakers was patented by Edward W. Kellogg and Chester W. Rice in 1924.

            Depending on the range of frequencies, loudspeakers can be divided into four- subwoofers, woofers, mid-range loudspeakers and tweeters.

Continue reading “What is a loudspeaker?”

            Developed in the 1870s by Englishman David Edward Hughes, carbon microphones were the first reliable form of microphones. They were widely used for many years before being replaced by other types that showed better performance.

            Structurally, a carbon microphone comprises carbon granules within a small container that is covered by a thin metal diaphragm. It requires a battery to cause current flow. By compressing and decompressing the carbon, sound waves change the amount of electric current flowing through the wire. This, in turn, creates electrical waves.

            The biggest disadvantage of carbon microphones was that they had a limited frequency and would not reproduce music effectively.

            On the basis of application, microphones can be divided into different types. The three most common ones are – dynamic microphones, condenser microphones and ribbon microphones. Let’s look at them in detail.

            Dynamic microphones are the most common and durable types, well suited for live sound. They work on the principle of electromagnetic induction, but take loud signals to move the coils.

            The next type of microphones is condensers. They use electrically charged capsules that are far more sensitive than moving coils of the dynamic mic.

            There are both large diaphragm condenser mics and small diaphragm condenser mics. The former is best suited for recording vocals, while the latter is great for high frequency instruments like acoustic guitar and cymbals.

            Ribbon microphones use corrugated metal ribbons that vibrate when pushed by air. But today, they are no longer popular. There is also a microphone known as the piezoelectric microphone. It uses a crystal of piezoelectric material to produce sound.

            A microphone, popularly called a mic, is a device we are all familiar with. It is in fact a part of our daily life and can be seen in almost all equipment around us. For example, computers, telephones, televisions, transmitters for commercial radio, tape recorders, hearing aids and public address systems for concert halls, all of them uses microphone.

            Technically, a microphone is a device that converts mechanical energy waves or sound into electrical energy waves.

            Let us see how the device works. When we speak, sound waves carry energy toward the microphone. Inside it, there is something called a diaphragm, which moves back and forth when hit by the waves. As a result, the coil attached to the diaphragm too moves back and forth. This results in the production of electric current, which flows out from the mic to an amplifier, or a sound recording device. Subsequently, the voice of the speaker is heard a loud. This is how personal address systems, electric guitars amplifiers etc. work.

            Sonomicrometry is a technique that makes use of the transmission of ultrasound energy through certain type of crystals and tissues to measure distance.

            It has a variety of applications, including measuring the distance between two fixed points in a soft tissue environment, and, quantifying the function and dynamics of cardiac, skeletal or smooth muscles. Traditionally, this technique has been used to determine cardiac function on large research animals like dogs, sheep, pigs etc. It was first done by Dean Franklin in 1956, and was quickly adopted by other biologists.

            At present, sonomicrometry is the most prevalent method to determine muscle length changes during animal locomotion, feeding and other bio-mechanical functions. Sonomicrometry crystals are usually implanted inside the skeletal or cardiac muscle tissues to track length changes during activities such as heart-beat, chewing etc. However, sonomicrometer devices cannot be used to treat or diagnose medical conditions in animals or humans.

           Animals are always thought to be intelligent enough to sense changes in environment. But a few studies in recent times suggest that some birds too are equally smart. For example, the golden winged warblers.

            In April 2014, a massive thunderstorm caused a series of tornadoes to tear through the Southern and Central United States. But something interesting happened just a day or two before this disaster – large flocks of golden winged warblers fled the area. Scientists say that the birds’ behaviour was caused by their ability to sense infrasound, which was an early warning sign.

            Other species that are sensitive to weather changes are seagulls and African guinea fowls. Apparently, seagulls get to hear low frequency sounds caused by large storms and also, earthquakes. This prompts them to fly inland before these disasters happen. So also is the case with African guinea fowls – they predict weather and change their nature accordingly.

            There are many animals that use infrasound for communication. One of the best examples is the elephant. Research has proved that the vocal communication of these mammals ranges down into lower frequencies. As a result, the sound waves get carried farther, and reach elephant groups that are located very far away.

            Interestingly, tigers also produced infrasound, along with a variety of other sounds. This is said to help them maintain their hunting grounds. Their low frequency sounds at 18 Hz and below, most of which are inaudible to humans, drive away rivals from their territory, and also attract mates. Such sounds not only cover long distances, but also penetrate dense forests.

            In addition to these two, there are many other animals that produce infrasound. Examples of these are giraffes, alligators, hippos, and marine mammals like humpback whales.

            Since time immemorial, there have been stories, legends, and reports on the sensitivity of animals towards different kinds of sounds.

            But the most commonly heard reports are on how some animals detect infrasonic sounds before natural disasters. As per one of the latest reports, animals like buffaloes, goats and dogs were found unharmed along the Cuddalore coast of India, where thousands died following the tsunami of 2004. People around the region said that many animals fled the area hours before the incident took place.

            Another group of animals that are said to have the ability to sense disasters are cats. Not just smaller animals, large once like elephants too grow restless prior to dangerous natural occurrences.

            Although many studies have been made, the reason for such strange behaviour in animals is yet to be confirmed.

            Infrasound can be defined as the low-frequency sound that is below 20 Hertz.

            For this reason, it cannot be heard by the human ear. Animals, on the other hand, are sensitive to such sounds. Research has proved that some of them can sense infrasonic sounds from natural events like earthquakes and volcanoes, and act accordingly. They can also use it for communication between each other.

            There are many uses of infrasonic sound. Primarily, it can be used to detect volcanic eruptions. Scientists use infrasound to track the passage of meteors through the atmosphere.

            There are many sources from where infrasound can come. They include large natural events like earthquakes, avalanches, volcanoes, and extreme weather events.

            In addition, man-made events such as explosions, wind turbines, aircraft breaking the sound barrier, and certain speakers too, produce it.

            The special characteristic of infrasound is its ability to cover long distances and get around obstacles with little dissipation.

            In the case of medical scans and non-destructive testing, experts use relatively low strength ultrasound waves. Much stronger waves are used for removing unwanted deposits like painful stones.

            Let us make it clearer. If we have problems caused by stones in kidney, gall bladder, or liver, powerful ultrasound waves are fired from outside our body in order to make the stone vibrate, and disintegrate. For this purpose, doctors now use what is known as an ultrasonic gun, which causes relatively lesser pain. The gun forces out short bursts of high frequency vibrations that cause the stones to resonate. These then smash the stones into pieces.

            A similar technique is used to destroy cancerous tumours and damaged regions of the brain called lesions. Here, ultrasound energy is applied to heat in order to destroy diseased tissues.

             Some of the most important applications of ultrasonics can be seen in the field of medicine. Ultrasonography or ultrasonic scanning is one of it, which uses high frequency sound waves to produce images of internal organs, vessels and tissues. This type of scanning is used to diagnose the condition of organs such as liver, kidneys or gallbladder.

            Then, there is something called obstetric ultrasound. It is a technique used during pregnancy to create images of a baby inside the womb.

    Another public health application of ultrasonics is in dental care. It enables the equipment called ‘descalers’ to remove plaque from teeth through a smoother and less painful experience.

            Yet another important use can be seen in the cleaning of equipment. What makes ultrasonic technology so popular in medicine is its effectiveness and affordability.

            Acoustic microscopy is a technology that helps in visualizing tiny structures using high frequency ultra sound waves. The microscopes in this fashion penetrate solid materials and create visible images of internal features, including defects like cracks and voids. For this purpose, they use frequencies up to several gigahertz.

             One of the most advanced types of acoustic microscopy is scanning acoustic microscopy. Here, the internal parts of a sample can be viewed without staining or causing any damage. It relies on a beam to scan the sample while it is in water.

            The difference between a traditional microscope and an acoustic microscope is that the former allows us to see only the surface of a specimen, while the latter obtains images from deeper layers. It also takes accurate measurements at a micro-level, which other microscopes may not be able to obtain.

          Just like humans, all forms of life in the Universe have the ability to hear, or sense things around them. But some of them have exceptional features for hearing, which enable them to survive better than others.

          One such animal is the elephant. Its hearing frequency is somewhere between 16 and 12,000 hertz, as a result of which, it can hear at a frequency 20 times lower than us.

          Another mammal that has a special auditory system is the fennec fox. It is a small species of fox seen in the sandy Sahara. It has large ears that play a vital role in hearing, as well as keeping the animal cool by spreading out during high temperatures. Other than these two, there are many animals that are sensitive to sounds. These include pigeons, owls, dolphins, etc. 

            As a matter of fact, no two species of animals look alike, or behave alike. Similarly, the abilities and senses of animals vary too, from species to species.

            One cannot expect a monkey to have the hearing ability of an elephant, nor can auditory ability between a marine mammal and a terrestrial animal be compared. Generally, it is seen that larger animals hear and use low frequency sounds, while smaller ones have with higher frequencies.

            However, there are always exceptions, as in the case of spade foot toads that can easily pick up low-frequency sounds. These are animals that live in desert habitats and spend their days buried in ground during dry seasons. They come out only when pools are formed after infrequent rains. And that is when their young ones are developed, before the water dries up.

            Similar to animals, birds and insects too have peculiar auditory features that help them adapt to surroundings.

          Kangaroo rats are unique animals that live in desert and dry, open areas. They are perfectly adapted to desert life, and can survive without drinking water, as they get moisture from their seed diet.

          But, what makes kangaroo rats special is their exceptional sense of hearing. It helps them detect enemies like owls and snakes, even when they are approaching from a distance.

          Kangaroo rats have large ear-drums and middle ears. However, the oval window between the middle and the inner ears is considerably smaller. This peculiarity helps the auditory system of the animal to magnify low frequency sounds by about 100 times.

          As a result, it can hear the sound of air flowing over the wings of an owl, or the scales of a snake moving across sand. Now, isn’t that a rare gift for an animal?

          The barn owl is a raptor that can be spotted on all continents except Antarctica. It is said to have extraordinary abilities that help in catching fast-running animals.

          The most predominant ability is the bird’s sense of hearing, which stands out for its sharpness. It is so superior that the bird can decipher the direction and height from which a sound comes! This is exactly what makes it a sharp hunter.

          Unlike others, the barn owl’s ability to hear is strengthened by its feathers. The heart-shaped facial disc made of stiff feathers helps the owl in picking up noise. It funnels any sound towards the ears, which open on either side of the bird’s head. The ruff of feathers is so important for this owl that without it, the bird cannot catch preys. And with it, even the slightest sound can be detected.

          Interestingly, a large portion of the barn owl’s brain is devoted to building sound maps of places!

          Bats are fascinating animals that have many unique features. One of these is the ability to sense a prey location using sound. Confusing, isn’t? Let’s get to know how they do it.

          Bats use the sound technique known as ‘echolocation’. It means determining the location of something by measuring the time it takes for an echo to return from it.

          As they fly, bats make calls, and listen to the returning echoes to build up a sound map of their surroundings. These sounds are produced by contracting their larynx. Measuring the time it takes for the echo to return, this smart mammal can predict at what distance its prey is!

          Usually, the calls of bats are pitched at such high frequencies that humans fail to hear them naturally. Another interesting fact is that bats can distinguish between obstacles and preys through echolocation, and can thus avoid the obstacles and catch the prey.

          How many of us have seen birds that don’t make sounds? Not many. Birds are in fact, most known for their ability to make sound, be it sweet chirping, or harsh caws.

          While humans and other mammals produce sound from the voice box or larynx, birds have a different organ for sound production – the syrinx. Located near lungs, it is a double voice-box that consists of a resonating chamber, and numerous membranes. As air flows over them, the membranes move back and forth, producing sound.

          There are different frequencies at which bird sounds come out. There are other birds too that can sing in high frequency ranges, like warblers, sparrows, wax-wings, kinglets etc. It is believed that one can never stop a bird from learning its own species’ song.

          Interestingly, many species have at least some mimicked sequences in their most common songs and calls.

               For a long time, it was believed that oceans were silent places. But, as science advanced, it was proved that most of the animals living in waters cannot survive without sounds. 

               We know for a fact that light reaches only till the surface of water. In the case of smell, it fails to spread far from their source, while under water. Contrary to this, sound waves find their ideal medium in water, and travel faster than in air. They move greater distances, and at the surface of water, get reflected back into the depths. That is why even the sound of surf crashing on to a rocky beach travels far into the ocean.

               In general, sounds help most marine animals to sense their surroundings, communicate, locate food, and protect themselves.

               Mammals like whales, for instance, identify objects like food and obstacles using low frequency pulse signals. Dolphins communicate through clicks and whistles. They use the technique of echolocation to detect and characterize objects.

          Sounds become part of a bird’s life from the very moment they are born.

          It is wrong to think that the only sounds made by birds are songs. There are a variety of others too, like alarm calls, begging calls, contact calls, flight calls etc., used by them, depending on the circumstances.

          Songs are of course the most distinctive and familiar sounds. They are used mainly to attract mates, mark their territories, or discourage intruders. The quality and duration of a song depend on the species. Some may have different songs for different times of a day, but some sing only in the morning or evening. The yellowhammer, for instance, repeats its song around 1000 times a day.

          Begging calls are usually made by young birds to draw attention. Contact calls, on the other hand, are used to signal one another, particularly while travelling in a flock.

          In addition, there is something called the dawn chorus. It occurs when a large number of birds sing at the start of a new day. This is done either to protect a territory, or to call in the flock.

          Whales are in general, highly social creatures that move under water in groups called ‘pods’. To communicate and socialize with each other, they use different kinds of sounds; namely, clicks whistles and pulsed calls. Let’s see what these sounds are, and how they help the marine mammals.

          Clicks are made by whales for purposes of navigation and identification of physical surroundings. They also help to distinguish between friendly creatures and enemies.  

          The other two sounds- whistles and pulsed calls- are exclusively used during social interactions. The latter which are similar to squeaks, or screams, is rather more frequent.

          Surprisingly, there are differing vocal dialects existing between different pods. Perhaps this is why whales can differentiate between familiar whales and stranger whales.

          In addition to the above mentioned sounds, the marine mammals also make loud slapping sounds on the surface of the water, using tails and fins. This can be heard for very long distances, and are thought to be warning signs, or a tool to scare other smaller fishes. 

               The list of the best ‘singers’ among mammals can never be complete without humpback whales. These aquatic animals are capable of producing complex series of sounds that are close to songs. The whale songs, as they are popularly called, consist of a variety of loud, low-pitched tones, moans, whines and grunts that are often melodious in nature.

               But most importantly, the songs have themes that are sung in a precise order, and change slowly over years.

               The songs typically last 8-15 minutes, and are repeated for several hours at a stretch.

               Unlike other ‘singers’, humpback whales do not produce sound through vocal cords, simply because they don’t have any. Their songs are created when air is pushed out of the blowhole located on top of the animal’s head.

               Interestingly, some male humpbacks, like the North Atlantic ones, can be heard singing the same song together even when they are miles apart. 

            For deep vibrations and low frequency sounds waves to travel thousands of kilometres under deep sea, there has to be some path to save them from diminishing. Else, a phenomenon like whale communication will never be complete. It is in this context that the SOFAR channel gains relevance. Technically, it stands for Sound Fixing and Ranging and allows low-frequency sound to travel great distances.

            Let’s try to understand the concept better. Some of you might know that sound waves are highly dependent on medium, salinity, temperature and density. That is, at different pressures or temperatures, the waves will travel at different speeds. At a lower temperature in water, the waves move slowly, but at a higher pressure, they speed up. This causes the phenomenon in a level of the ocean called the SOFAR layer or channel.

            The advantage of this channel is that it allows sound waves to move without dissipating much of their energy. And if there is no energy drop, it means a wave can travel longer distance. 

          The howler monkey is a large type of monkey that can be spotted in the rainforests of South and Central America. Its strange name comes from the fact that its calls are louder than any other types of monkeys.

          There are quite a few kinds of sounds produced by the howlers. This includes loud grunts, roars, and barks and of course, howls. The monkeys are most vocal at dawn and dusk. A troop’s cries give information about their size and location.

          Now you may wonder how loud howler monkeys are. In fact, they are believed to be the loudest animals in the world. When a troop gets together and start howling, barking and grunting, the sound can be heard up to 4.8 kilometres away!

          What helps them produce such loud calls is the hyoid bone. This is a structure located near the neck that looks like a horseshoe in humans, but in howler monkeys, they are larger and more cup-like. It allows the animal to produce a single roar that lasts for about 8 seconds. 

            Drums are percussion instruments that have a thick membrane or skin, stretched tightly over its hollow body. They have been used for a long time, and are played with sticks, mallets, or hands. When the instrument is struck, the skin gets pushed down. It then starts vibrating, going up and down multiple times in a second. When this vibration pushes the air, sound waves are created.

            There are many factors that affect sound production in drums. If the head portion of the instrument is large, it produces a low-pitched sound. With a large body, drums absorb higher frequency sounds, while amplifying lower frequencies. As a result, a warmer tone will be produced. If the body is small, the sound generated will be sharp and bright.

            Another important consideration is the volume of air inside a drum. The higher the volume, the lower will the notes be. A further factor is the way with which the instrument is struck. 

              Wind instruments are those musical instruments that produce sound when air is blown into or across its mouthpiece. There are a variety of them used by musicians since time immemorial. The list includes flute, saxophone, clarinet etc. Many of them look similar with long tubes of various sizes and metal keys that cover the holes when played to make notes. In general, bigger instruments produce low pitched sounds.

               Depending on the material with which they are made, wind instruments are divided into two- brass instruments and woodwind instruments. In the former, sound is produced when the player’s lips vibrate, which in turn causes air inside the instrument to vibrate too. Examples of this are horns and trumpets.

              In the case of woodwind instruments, there are different ways with which sound is generated. Let’s look at an example of the most popular one- the flute. Here, an amount of air is gradually blown through the small mouthpiece. When this column of air gets trapped within the instrument, it vibrates, and produces the beautiful sound. There are of course factors that influence the final output.

          String instruments are those which make notes by vibrating. The best examples are the guitar, violin, piano etc. To play them, one has to make the strings vibrate by striking, plucking or rubbing a bow against them.

          Generally, string instruments have something called a sound box or resonator, which amplifies the sound. Each of them, however, works in their own way. For example, a guitar produces sound when the player plucks the string, either using a finger, or a piece of plastic called plectrum. The length of the string is fixed, and controlled by the player himself.

          There are different factors influencing sound in a string instrument, and the most important ones are length, weight, and tightness. If the strings are long, the vibration created would be slower, making lower sounding notes. 

            Electronic music generally refers to music created using electronic equipment. That is, any sound created by the means of electrical signals could be called electronic.

            Production of such music involves the use of power amplifiers as well as loudspeakers. Instruments such as synthesizer and electronic organ are examples of this. In these, oscillators produce electric signals with same frequencies as musical notes. The signals are then pushed to loud speakers. Subsequently, they cause the loudspeaker to vibrate, and produce musical sounds.

            History records that the earliest electronic equipment was invented sometime in 1897. It was called the teleharmonium, believed to have been developed by Thaddeus Cahill. But since it weighed around seven tonnes, the instrument was inconvenient for use. The first practical electronic musical instrument is considered to be the theremin, invented by Leon Theremin in 1919 – 1920. Since then, many more equipments have been developed till date. 

            Acoustics is the branch of science that deals with the production, control, transmission, reception and effects of sound.

            The word ‘acoustics’ has come from the Greek term akoustikos, meaning ‘for hearing’.

            Let’s see why acoustics is relevant. When a concert hall or a theatre is built, the architect needs to plan how sound waves travel through the air, so as to make sure everyone hears the same sound, clearly.

            Here, sound may be balanced using soft absorbent materials like curtains, carpets, plaster etc. Next, take the case of a doctor. He uses high pitched ultrasound waves in order to see the interiors of the human body.

            The wonders of acoustics have been seen in the world since centuries. The Greeks were known to be one of the earliest users of this technology.

            Today, there are many examples that demonstrate acoustics. One such is the Sydney Opera House in Australia.