Sound Production Flashcards
What is sound?
A local pressure disturbance in a continuous medium (air/sea) that contains frequencies in the range of 20 to 20,000 Hz (the audible range)
Who does the definition of sound apply too?
Only humans, not all humans can hear sounds of that range
What is the audible range for sound?
20-20,000hZ
What is a single sound wave caused by?
An increase in pressure at a certain point in an elastic medium which causes a domino effect
What happens if a perturbation is repeated periodically?
It generates a series of sound waves - vibrating source, causes an increase in pressure
What does a wave tell you?
The crests respond to high pressure points and the troughs correspond to low pressure points
Where does sound propagate from?
The source at equal speed in all three dimensions
What are sound waves?
Spherical waves - because sound expands in lots of different ways, not just in a straight line
What does the speed at which sounds propagates depend on?
The type, temperature and pressure of the medium through which it propagates
What is the speed of sound in dry air (20 degrees)
343m/s - 1 meter every 2.9 milliseconds - this is so fast that speed is almost irrelevant
What is the simplest representation of sound? - how we record sound
A waveform - the temporal variation of sound pressure as a fixed point in space
What happens when we record sound?
We record a temporal variation - sound pressure at a fixed point in space
What are most sounds generated by?
Produced by oscillators - means that you give a little energy now and then and they will work at their own frequency (being on a swing)
What are most sounds?
Periodic - one that repeats itself at regular intervals
Why are oscillators useful?
Because you don’t need to control them, just give a little energy and the will move back and forth, creating a periodic sound wave
The pressure variation of a periodic sound is an oscillation with a given..
Period
Amplitude
The period of a sound wave
The duration of a oscillation cycle
Can be measured as the time between two peaks
The frequency of sound
Used more than period
The number of air pressure oscillation cycles per second - it is the opposite of the period
Frequency = 1 divided by period by T
What is one single oscillatory cycle per second?
1hz - not audible
Types of oscillatory cycles
125 (the fundamental frequency is male voice) = 125hZ
200 - fundamental frequency in female, 200Hz
2000 - some bird calls, 2000 hz
15000 - some bat calls - 15000
What does fundamental frequency mean?
The lowest frequency which is produced by the oscillation of an object
The amplitude of sound
This is the loundess
This is the magnitude of the change in sound pressure within the wave - maximum amount of pressure at any point in the sound wave
Also called sound pressure level
How is amplitude measured?
Decibels
What is loudness?
The perceptual correlate of amplitude - it isn’t a scientific measure, it is subjective, non linear perceptual attribute which varies with period, frequency and distance
What are the ways of representing sound?
Waveforms
Spectrograms
Spectrums
What is a waveform?
Represents sound in terms of time and amplitude (energy)
What is a spectrogram?
Represents energy (amplitude) as a function of time and frequency Energy is represented by different shades of grey, if dry what, no energy at time or frequency. Energy isn't present at all frequencies
What is a spectrum?
Measures energy as a function of frequency - time is removed
A peak tells us how much energy there is at each Hz
What are simple sound waves?
Pure tones
Simple frequency tones with no harmonic content - sine wave
Only has energy at one frequency e.g. a beep
Nothing above or below 1.5 kZ - frequency of a single tone
don’t use this for communicating
What are complex sounds?
Animals humans and most musical instruments usually generate sounds which have energy at more than one frequency - complex sounds
Composed of more than one tone
They are periodic and repeat themselves
have harmonics and a fundamental frequency
