My Science School

               At sea level, sound travels though the air at around 340 m pet second, and slightly slower at high altitudes. The denser the substance, the faster sound will travel through it. Sound travels at 1,500 m per second through water, for example. When travelling at such very high speeds, an aircraft begins to build up a huge wave of compressed air in front of it. This was known as the sound barrier because it was an obstacle to high-speed flight. When the aircraft exceeds the speed of sound, it leaves the built-up waves of pressure behind, and these break away, forming a ‘sonic boom’. The speed of sound in air is called Mach 1, and the speed of supersonic aircraft is measured in Mach numbers. Concorde is the only commercial aircraft to have broken the sound barrier.

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               You will have noticed that as a car travels quickly towards you, the sound of its engine gets higher, and then becomes deeper after the car has passed by. This is called the Doppler Effect. What happens is that as the car approaches, the frequency of the sound of its engine increases as the wavelength of the sound decreases. Each successive sound wave is a little shorter as the car comes towards you. Then as the car moves away, the process is reversed; the frequency decreases while the wavelength of the sound becomes longer.

               You will not notice the Doppler Effect if a supersonic aircraft flies past, because you cannot hear the sound of the plane until it is actually flying away from you.

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                   Like light, sound can be reflected from certain surfaces. Hard surfaces such as rock or the side of a building reflect sound well; as the sound bounces back you hear an echo. The delay in hearing the echo is due to the comparatively slow speed of sound. Soft materials absorb sound and will not produce an echo. This is why recording studios are lined with felt material, which prevents any unwanted noise from interfering with the recording.

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               Compared to other animals, the human ear is not very sensitive. We can hear sounds with a frequency of up to 20 kilohertz (kHz) — a normal speaking voice is about 1 kHz. Bats, dogs and some insects can hear sounds has are pitched much higher, which we cannot hear at all. Children can usually hear a bat squeaking, although this sound can sometimes be as high as 120 kHz, but in adults the ability to hear these high-pitched sounds is usually lost. ‘Supersonic’ dog whistles are used to call dogs, and their sound is so high-pitched that humans cannot hear it at all.

               Sound is a form of vibration passing through the air or some other material. Sound travels in the form of waves but, unlike electromagnetic waves, sound waves cannot pass through a vacuum. The frequency of a sound wave controls its pitch. Long wavelengths produce deep sounds, while short wavelengths produce higher sounds. The loudness of a sound depends on the height of the sound waves, or their amplitude. The higher the amplitude, the louder the sound.

               Sound vibrations are received in your ears. They are conveyed to a mechanism inside your ears that first amplifies them, and then converts the vibrations into signals that your brain interprets as sound.

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          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.