Hello,
My name is Ajinkya Kharote from Mumbai, India .
In
my first week assignment I will be talking about the Basics of Sound.
What is Sound?
Sound
is a type of energy made by vibrations.
An
object produces sound when it vibrates in matter. The matter could be
a solid, liquid or gas. Most of the time, we hear sounds traveling
through the air(gas) in our atmosphere.
When
something vibrates in the atmosphere, it moves the air particles
around it. Those air particles in turn move the air particles around
them, carrying the pulse of the vibration through the air. This goes
on until the pulse loses its energy. If your ears are within the
range of this pulse, you hear the sound.
let's
look at a simple vibrating object: A tuning fork. When you hit it,
the metal vibrates i.e., flexes in and out. When it flexes out on one
side, it pushes on the surrounding air particles on that side. These
air particles then collide with the particles in front of them, which
collide with the particles in front of them, and so on. Leading to a
slight rise in air pressure. This is called compression.
When
the tuning fork flexes away, it pulls in on the surrounding air
particles. This creates a drop in pressure, which pulls in more
surrounding air particles, creating another drop in pressure, which
pulls in particles even farther out. This pressure decrease is called
rarefaction.
Sound
waves are longitudinal waves, All it means is that the direction of
propagation of sound (Energy) is the same as the particles. But as you
can imagine it is very difficult to represent a longitudinal wave. To
make the representation easier the waves are represented as
transverse waves. We must keep in mind that the particles and wave
move in same direction.
So
sound waves are longitudinal waves, that travel through air at a
speed of roughly 340m/sec or 1km/3 sec.The speed of sound changes
according to change in temperature, humidity, the elevation above sea
level. these changes are really small and our ears are very very good at measuring these small
changes. That is why we can determine whether a sound is coming from
our left or right and things like how far the sound is coming from
etc. By understanding these things we can manipulate the delay and
loudness of sound coming from our speakers to give a specific effect.
We
hear different sounds from different vibrating objects because of
variations in the sound wave's frequency, amplitude and timbre.
Amplitude :
Amplitude
is the extent of compression and rarefaction in the air. We perceive
this as the amount of loudness of sound. So higher the
amplitude (Movement of particles from original position due to the
wave), louder the sound. Again loudness is something that we feel or
perceive. There is no way to measure loudness but we can measure
amplitude of a sound wave.
Amplitude
is measured in decibels. In air it is measured in dbspl(Decibels of
sound pressure level) 0 being the quietest sound that we can hear and
then it goes up from there, as one can easily imagine this is a
relative scale as the zero level will vary . In digital terms that is
in computers we use dbfs(Decibels of full scale) 0 being the loudest
that can be represented in numbers and then the scale goes negative
from there.
Frequency :
It is the measure of how many times the wave passes in a given amount of time. The rate at which the movement of particles is repeated. A
higher wave frequency simply means that the air pressure fluctuation
switches back and forth more quickly. We hear this as a higher pitch.
When there are fewer fluctuations in a period of time, the pitch is
lower.
If a particle of air undergoes 1000 cycles of vibration in 1 second, then the frequency would be 1000 vibrations per second. The unit commonly used for measuring frequency is Hz (Hertz).
Where,
1 Hz = 1 Cycle / Second
1 kHz = 1000 Cycles / Second
The picture below shows time horizontally and amplitude vertically.
A thing to remember about frequency is when you double the frequency you hear a sound an octave higher.
Timbre :
Timbre of sound is the quality or character of a sound. Whenever any musical instrument creates any sound it creates waves of multiple energies (Harmonics / overtones) . This results in different patterns of wave form for every source. We can say that the pattern of vibrations in a cycle is different for each instrument. Two same instruments will also produce slightly different sounds. This difference is due to timbre of the sound. The wave form for a same tone or note will be different for all instruments.
As you can see the frequency and amplitude is same but timbre is different. That helps us in recognizing different instruments or that is the reason we can tell who is talking/Singing. The timbre of each individual is different.
Summery:
Sound is result of an object vibrating in air. It travels in the form of longitudinal waves. The speed of sound changes according to the surroundings. Any sound has 3 more properties Frequency (Pitch) , Amplitude (Loudness), Shape of wave form (Timbre). All these including the speed are independent of each other. And we can measure/manipulate these things (frequency, amplitude, timbre, delay in left and right speakers) to give all kinds of sound effects.
