musical instruments and sound simple harmonic motion envelope of sound nihl report aud202 audio and...
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Musical Instruments and SoundSimple Harmonic Motion
Envelope of soundNIHL report
AUD202Audio and Acoustics Theory
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Wave Interaction / Phase ConceptsBeat Frequencies / Comb Filtering
Harmonics and Overtones
Comb Filtering
A wave delayed by 180 degrees (half a
wavelength) results in the fundamental frequency of cancellation.
Frequencies delayed by 1.5x, 2.5x, 3.5x the wavelength will cancel, while whole number multiples (1, 2, 3 etc) will reinforce.
Comb Filtering
A wave delayed by half a wavelength results in the fundamental frequency of cancellation
Comb Filtering
Common causes of comb filtering:
1.Two microphones at different distances from the same source.
2.Reflective nearby surface causing a reflected sound to arrive at the microphone slightly after the direct sound.
3.Two identical sounds in a DAW with a 1 to 10ms delay
Comb Filtering Question
If one mic is positioned 2 metres from a sound source and another mic is 3.5 metres from a sound source, what will be the fundamental frequency of cancellation if they are combined?
Noise
White noise: Equal energy per frequency
Pink noise: Equal energy per octave
Pink noise is simply White noise with a ‘pinking filter’ added (-3dB/octave roll off)
ADSR (Attack, Decay, Sustain, Release)
Attack initial run up of levelDecay decay in the signal directly after the attackSustain level during the main sequenceRelease how quickly the sound fades
Resonant Frequencies
A resonant frequency is a natural frequency of vibration determined by the physical parameters of the vibrating object
Resonant frequencies of a body are frequencies at which energy is most efficiently converted to physical displacement
Resonant Frequencies
1. It is easy to get an object to vibrate at its resonant frequencies, hard to get it to vibrate at other frequencies.
2. A vibrating object will pick out its resonant frequencies from a complex excitation and vibrate at those frequencies, essentially "filtering out" other frequencies present in the excitation
3. Most vibrating objects have multiple resonant frequencies.
Different instruments employ different methods to create pitches
•String instruments use strings•Wind instruments use a vibrating column of air•Percussion instruments use methods such as bars, membranes and plates
Standing Wave in Stringed Instruments
Include: violin, cello, guitar, bass etc
The standing wave constraint of string instruments is that at each end of the medium there must be a node.
They can produce a fundamental and all odd and even harmonics
Stringed Instruments
• The bridge lifts the strings so they can vibrate with the air as well as amplifying the strings
• The soundboard radiates with the strings helping to amplify the sound
Wind Instruments
Wind instruments include brass and woodwind families (categorised by the type of reed used)
Brass: trumpet, trombone, french horn, tuba, didgeridoo. Uses Lip Reeds.
Woodwind: flute, recorder, saxophone, oboe, clarinet, bassoon. Uses either Mechanical or Air Reeds.
Wind Instruments
Lip Reed (brass) instruments vibrate under the influence of the air flow.
Mechanical Reed (woodwind) instruments have a flexible reed or reeds at the mouthpiece, forming a pressure-controlled valve
For Air Reed (woodwind) instruments such as the flute, the flow of air over the mouth of the instrument forms a flow-controlled valve.
Speed Writing Exercise
List ANYTHING that might cause NIHL
List occupations where NIHL might be a problem
List ways to avoid NIHL