Transcript MUSICAL SOUND

MUSICAL SOUND
What is sound?
•Aural perception vibrations
The aural vibrations can be music or noise.
The definition of music is subjective hence one’s
noise might be another’s music.
Properties of sound
• To perceive sound depends on the
following three factors
• Production of sound which takes place in a
vibrating body, material /mass i.e. sound
source.
• Propagation i.e. the traveling of sound via
a medium( air, liquid and solid)
• Perception through the ear or microphone
which receives the sound
Production
• An object is set in motion transferring
mechanical energy into acoustical energy.
• The acoustical energy forms pressure
waves in the medium e.g. in air the
vibrating objects create sound
• There are so many things around us that
vibrate and produce sound try to identify
them.
Propagation
• Sound travels through some medium for it to be
perceived e.g. air, water, solid object etc,
• The vibration creates a disturbance in the
medium (air) creating pressure below and above
the atmospheric pressure i.e. compressions and
rarefactions.
• The compressions and rarefactions move away
from the sound source in all directions. The
molecules do not move with the sound but they
are just dislocated from the original position.
• Only the sound wave moves away from the
source in a longitudinal waveform.
Perception
• This when sound is received and interpreted, the
ear is a good example.
• The study of perception of sound is called
psychoacoustics.
• Perception involves two aspects: Pitch i.e.
(height and depth) and Loudness the strength
and weakness of sound.
• From an acoustic viewpoint the above referred
two properties are called frequency and
amplitude
Perception cont,
• Volume is the psychological measurement of the
magnitude of sound including its frequency,
pressure, harmonics and surface properties
within the space and time
• Timbre is the unique characteristic quality of
sound given by its overtones and the harmonic
content of the fundamental frequency gives the
tone colour, relative amplitude of overtones as
they change over time
Waveforms
• A visual representation of a wave for the
purpose of understanding properties
thereof.
• Longitudinal waves are one kind of
waveforms.
Characteristics of wave forms
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Frequency
Wavelength
Envelope
Amplitude
Velocity
Harmonics
Surface properties and propagation
characteristics
Frequency
• Rate at which a vibration reiterates a complete
cycle of one compression and rarefaction.
• A cycle has 360 degrees of a circle
• A cycle is made up of two halves one above +ve
(compression) and the -ve (rarefaction) below
the horizontal line.
• The crest of the compression depicts maximum
density with that of rarefaction denotes
maximum expansion.
Hertz (f)
• The rate at which the cycle occurs per second is
measured in Hertz (Hz).
• An object or anything that vibrates at the rate of 600
complete cycles per sec has a frequency of 600 Hz
• Musically a violin playing a note C4 i.e. middle C is 262
Hz. If A4 is 440 Hz then A4 has a higher frequency than
262 Hz
• The higher the frequency the higher the perceived pitch
and vice versa.
• Frequency is dependent upon time hence the sound
does the same linearly.
How to work out frequency
Frequency= (v) velocity
(w) wavelength
If the wave length of a sound is 1metre
V is 344m/s
The frequency is 344 Hz
Wavelength
• The physical distance in metres of a complete cycle
• The longer the wave form the lower the freq hence the
lower the perceived sound and vice versa
• Longer wavelengths occupy more physical space
• The lowest perceivable pitch has the a wavelength of
17m, 20Hz
• Wavelength= Speed of sound (V)
frequency
f
Period
• The time it takes for a cycle to occur and is
measured in seconds
• T= 1
f
Velocity of sound
• Air is a nondispersive medium hence all sounds regardless of the
frequency travel at the same speed and occupy the same space at
the same time. Reason we perceive the performance of a choristers
at the same time.
• The standard speed of sound is 344m/s or 1239km/h (1130ft/s, 770
m/h)
• THIS STANDARD IS MEASURED AT ROOM TEMP 20º c, 70%
Humidity,
• Higher temps increase the speed of sound, for every decrease or
increase in degrees of temp add or subtract 0,6m the standard
measurement
• V= 0,6 m/s x y
Amplitude decreases with increasing
distance
Distance in metres
10 m
20 m
30 m
90dB
84dB
78dB
Sound Source
Amplitude
The envelope of a wave
Refers to characteristic of attack and decay of a sound thus envelope involves
ADSR
• All sound possess specific envelope and can change with the environment
occupied.
• Reverberant spaces exaggerate envelope as opposed to dry spaces
Attack
Decay
Sustain
Release
Attack is the sudden increase in amplitude to full intensity
Decay the sound intensity decreases to a point
Sustain the sound is held and then
Release the sound attenuates
The Frequency range in Human
hearing
• About 20 Hz to 20 kHz
• All the sounds that we are able to hear fall
within this range.
• Frequencies below this range are said to
be subsonic, whereas those above it are
ultrasonic.
• Though not heard the of vibrations sounds
outside the hearing range can be felt
Some animals have a wider range of
hearing
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NAME
Cat
Dog
Bat
Dolphin
Lowest
45 Hz
50 Hz
10 kHz
1 kHz
Highest
85 kHz
45 kHz
120 kHz
200 kHz
Musical considerations for human
hearing
• The human hearing range is large within the
musical context.
• Non musical sounds form a greater spectrum of
frequencies more than the fundamental tones of
music.
• Music takes 25% of the hearing range with the
noises occupying the whole hearing range.
• Fundamental tone in music is that which is heard
(core pitch) prominently when an instrument is
played. This occupies 50% of the total sound
perceived.