L1 Sound Flashcards
(34 cards)
Sound is produced by a rapid variation in the average _______ or ________ of air molecules above and below the current ____________.. Minute changes in __________ are referred to as sound pressure and the fluctuations in pressure as sound waves
Sound is produced by a rapid variation in the average density or pressure of air molecules above and below the current atmospheric pressure.. Minute changes in atmospheric pressure are referred to as sound pressure and the fluctuations in pressure as sound waves
Higher pressure areas = ________
Lower pressure areas = ________
Higher pressure areas = ‘compressions’
Lower pressure areas = ‘rarefractions’
What sort of tone is a sine wave?
A pure tone
What 3 parameters uniquely define a sine wave, and are used to describe complex sounds?
Period
Amplitude
Phase
What is the period of a sound
The period is the duration of one cycle of a sine wave
It is the time it takes for an air molecule to oscillate back and forth one time.
What is amplitude?
The strength or level of sound pressure.
Amplitude—distance between the resting position and the maximum displacement of the wave.
What is phase?
Phase – Phase specifies the location or timing of a point within a wave cycle of a repetitive waveform.
What is frequency?
The number of complete cycles in a second
Unit of measurement: 1 Hz = 1 period per second
- Frequency is inversely related to the period (T) i.e frequency = 1/period (F=1/T)
What is a waveform? What are the disadvantages of using a waveform?
Way of displaying a sine wave. Display of time against amplitude
Difficult to get frequency from this
What is a spectrum?
Way of displaying a sine wave.
Focuses on what is happening in terms of freq (freq domain). Display of freq against amplitude within each freq component represented by a vertical line – easier to work out frequencies of sounds
What are complex sounds?
Sounds made up of many sine waves
‘Any perodic vibration, no matter how complicated in seems, can be built up from sinusoids whose frequencies are integer multiples of a fundamental frequency, by choosing the proper amplitudes and phases’
What is a complex periodic waveform?
- made up of sine waves w freqs that are multiples of each other e.g 100Hz, 200Hz, 500Hz)
- Component sine waves = ‘harmonics’ and the components are said to be ‘Harmonically related’
What is the fundamental frequency?
Freq of repetition of the waveform. All other harmonics are multiples of this freq.
Fundamental freq is always the first harmonic
Different types of complex periodic waveforms (e.g sine, square, sawtooth) have different _______
Timbres
What are complex aperiodic waveforms?
- made up of sine waves w freqs not related to each other e.g 100Hz, 222, 278 etc
- The complex sound sounds discordant; the waveform does not repeat in a regular pattern
- Aperiodic sounds which contain many components that are not harmonically related are perceived as ‘noise’ (e.g pink noise, white noise)
Why is dB a ‘relative measure’?
a decibel value is always relative to a reference level so it describes a ratio between 2 sounds
What is a logarithmic scale used for in sound?
A logarithmic scale is used to compare ratios in a decibel scale. This compresses an enormous range of ratios into something manageable
What are the 2 essential components for resonance to occur?
Sound sources & resonating cavity
What is a Helmholtz resonator?
It is a resonator which responds best to (ie amplifies the intensity of) a frequency determined by the size of the resonator: ‘resonant’ frequency
What is the ‘response’ of a resonator?
the effect of the resonator on the intensity of the input sound (e.g a response of 2 means it will be twice as intense as before it went through the resonator)
How many resonant frequencies does a simple resonator have?
1
How many resonant frequencies does a complex resonator have?
more than one resonant frequency
How many peaks will the transfer function of a simple resonator have?
1
How many peaks will the transfer function of a complex resonator have?
Multiple peaks
