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Sound is a means of communication
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Communication involves 3 basic elements:
1) Stimulus
2) Medium
3) Reception
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Sound is produced in the form of a pressure wave caused by vibrationsFrequency
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The rate of vibrations determines the frequency of the sound
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Frequency is defined as the number of cycles per second
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Frequency is measured in Hertz (Hz)
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Frequency is related to pitch
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Frequency spectrum for the human ear is 20Hz to 20000Hz
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The human ear does not perceive each frequency in the spectrum at an
equal level of loudness
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A common unit used to measure sound level is db SPL (Sound Pressure
Level in decibels)
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Phon is a measure of perceived loudness
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High frequencies contain more directional information while low
frequencies tend to be more omni-‐directional
Wavelength
The physical dimension of 1 complete cycle
High frequencies have shorter wavelengths
Low frequencies have longer wavelengths
Longer wavelengths have more energy
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The displacement in time of a wave
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Phase shift occurs when waves of the same frequency are not similarly
displaced
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Can result in total cancellation of a particular frequency
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Phase interference is commonly a result of direct and reflected sounds
Harmonic Content
Harmonics are integer multiples of the fundamental frequency
The fundamental frequency provides the basic tone of a soundOctaves
An octave is the 8 note separation of a scale in modern music
It is a halving or doubling of frequencyWaveforms
Can be simple (a sine wave) or complex (speech)
White noise has equal energy per frequency
Pink noise has equal energy per octaveAcoustic Envelope
An important aspect influencing the waveform of a sound is its envelope
Every instrument produces its own envelope which works in combination
with its timbre to determine the subjected sound of the instrument
The envelope of a waveform describes the way its intensity varies from the
time that the sound is produced until it dies away
The envelope describes a relationship between time and amplitude
An acoustic envelope has 4 basic sections: Attack, Decay, Sustain and
Release
Dynamic range is the difference between the softest and loudest parts of a
sound
Haas Effect
2 similar sounds arriving within 30ms of each other will be perceived as 1
single sound. However, the earlier arriving sound will provide location
information
Feedback Loop
A feedback loop occurs between of an output signal and an input signal