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Sound by Mind Map: Sound

1. audible disturbance in a medium that is produced by a vibrating source

2. sensation we feel when acoustic energy enters our auditory system

2.1. Sound energy

2.1.1. emanating from a single point source.

2.1.2. As it expands, energy is transferred outward.

2.1.3. Energy is conserved

2.2. Range of Sounds We Can Hear

2.2.1. Faintest sound you can hear = 10-12 watts/m2 or 0.000000000001 watts/m2

2.2.2. Pain = 1 watt/m2

2.2.3. Damage = 1000 watts/m2

3. essential elements

3.1. source of energy

3.2. vibrating body

3.3. medium

3.3.1. physiological response: if you believe there needs to be someone to hear the sound for the sound to exist

3.3.2. propagation through a medium compression region of compressed molecules higher than atmospheric pressure rarefaction region of air molecules that are more spread out than at normal atmospheric pressure lower than atmospheric pressure

4. wave

4.1. a disturbance travelling through an elastic medium.

4.1.1. Transverse Waves a moving wave that consists of oscillations occurring perpendicular

4.1.2. Longitudinal Waves a wave vibrating in the direction of propagation

4.2. one region of a medium is disturbed, it wants to return to its normal location

4.3. attributes of sound waves

4.3.1. waveform A graphical representation of a sound depicting the changes in pressure that occur over time.

4.3.2. cycle

4.3.3. frequency The number of vibratory cycles that occur per unit of time.f = number of cycles / second number of compressions and rarefactions/second f is related to the psychological sensation of pitch. The higher the f, the higher the apparent pitch.

4.3.4. period The time required for a single vibratory cycle T = 1 / f

4.4. types of sound waves

4.4.1. Complex waves A complex sound is any sound wave that is not sinusoidal. When multiple sine waves are added together, they result in a complex wave. Fourier’s Theorem The degree of complexity of a complex sound wave depends on the number of sine waves that are combined and on the specific dimensional value (A, f, phase) of these components. Fourier analysis Complex Periodic Sound Waves have a discernible pattern that repeats itself example: For speech – vowels and some consonants have waveforms that are nearly periodic components of a complex periodic sound Complex Aperiodic Sound Waves no discernible pattern Vibratory motion is random Components - called components (they are not called harmonics) types of complex aperiodic sound waves

4.4.2. Sine waves Phase The time difference between two sinusoid signals measured in terms of the angle separating the two signals. Pure Tone

5. how is sound measured?

5.1. frequency

5.1.1. Octaves A musical interval is a relationship between two frequencies. (1/2)f = an octave below f

5.1.2. The higher the f, the higher the apparent pitch.

5.1.3. f = 1 / T

5.2. amplitude

5.2.1. The strength of a wave as reflected in the size of variations in pressure. Peak (Ap)- reflect the size of variations from "zero" to the maximum. Peak to peak (Ap-p)- reflect the size of pressure variations from minimum to a maximum.

5.2.2. RMS (ARMS) reflects the average amplitude of the signal by taking the average amplitude value of the waveform. For a sine wave, ARMS= .707 x Ap

5.2.3. measured in Volts

5.2.4. Decibel commonly used convention for scaling the amplitude of a signal log ratio scale shows the amplitude of a signal relative to that of a reference signal. Intensity level indicates that we are using a reference intensity Zero dB means that the measured intensity or sound pressure equals the reference intensity or sound pressure (it does NOT mean there is no intensity or sound pressure). Negative dB means the observed intensity or sound pressure is less than the reference. (try an example of this on your own)

5.2.5. The Inverse Square Law As one moves further and further from a sound source, the amplitude of the signal becomes weaker and weaker. Sound radiates in a sphere from the source. Conservation of energy requires that the existing energy must ‘cover’ the ever expanding sphere. Some energy is lost to friction and environmental obstacles As the distance from a sound source changes, the intensity of the sound varies indirectly as the square of the increased distance from the source. 1 / ( r1 / r1) ^ 2

5.3. wavelength

5.3.1. The distance in a medium between a region of compression and the next region of compression. λ = c/f c = 1100 ft/sec

5.4. Signal Strength can be expressed as:

5.4.1. Sound Power the RATE at which work is done – or rate at which energy is transferred or transformed to measure add up the amount of energy over the entire surface of the sphere. watts or work/unit time

5.4.2. Sound Intensity in watts/m2 dB (intensity) = 10 * log Im/ Ir Doubling any level of intensity (ratio of of new to previous level of intensity is 2:1), the dB value is increased by 3 dB.

5.4.3. Sound Pressure Hearing is directly related to sound pressure unit of measure is: μPa or dynes/cm2 Amount of force/unit area Reference Values (Pr) .0002 dyne/ cm2 or 20 μPascals (μPa) dB SPL = 20 log po/ pr Doubling any sound pressure (ratio of of new to previous sound pressure is 2:1), the sound pressure level is increased by 6 dB. Any sound pressure (or intensity) equal to the reference is 0 dB Measured SPL = 20 μPa

6. Filters

6.1. a device that blocks some things that try to pass through it while permitting other things to pass through

6.1.1. Physical

6.1.2. Acoustic examples: paper towel tube also involved in speech production

6.1.3. Electronic

6.1.4. Digital

6.2. The effect of filtering is separting things that were previously mixed together

6.3. Types of idealized filters

6.3.1. Hi pass

6.3.2. Lo Pass

6.3.3. Band Pass

6.3.4. Notch

6.4. Characterizing a filter

6.4.1. Center Frequency

6.4.2. Bandwidth