Sound Theory Flashcards by Hayley Roscoe

Hertz is named after who? Why?

Named after Heinrich HertzHe was the first person to conclusively prove the existence of electromagnetic waves

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What is the generally accepted range of human hearing?

20 Hz - 20 kHz

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What affects the speed at which sound travels?

Temperature and density of the given medium

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What is a decibel?

1/10th of a Bel

A dimentionless unit used to describe a ratio of either power or pressure; needs two values to have meaning

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When a sound is louder, how does it affect the frequencies?

As sound gets louder the frequency response becomes more linear—you perceive all frequencies more evenly rather than perceiving some frequencies as being louder than others

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What is the threshold of pain?

approx. 120 dB

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How loud is normal conversation?

Approx 60 dB

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What is white noise?

All frequencies at the same actual volume

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What is pink noise?

All frequencies as the same perceived volume

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DEF: diffusion

The scattering of sound waves evenly throughout a given space

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DEF: refraction

A change in direction of a sound wave caused by the sound wave hitting a medium through which the sound travels differently

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DEF: absorption

When sound waves are absorbed into a medium and converted from sound energy into heat

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DEF: diffraction

The bending of waves around an obstacle or spreading out of waves beyond small openings

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How do high frequencies react when diffracted?

They are highly directional either focusing as they pass through an opening or being blocked by an obstacle

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What is the speed of sound at 21° C?

343.6 m/s (344 m/s rounded up)

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How does density of a medium affect the speed of sound?

The more dense the medium, the faster sound travels. sound travels fastest in solids, then liquids, and more slowly in gasses

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How does temperature affect the speed of sound?

Sound travels faster in warmer temperatures and slower in cooler temperatures

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How do you calculate the distance a sound is travelling?

d = c x t (Distance = speed x time)

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How do you calculate the time a sound will take to travel at a certain distance ?

t = d/c (Time = distance / speed)

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How do you calculate the speed at which a sound is travelling?

c = d/t (Speed = distance / time)

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What is sound, technically?

Sound is fluctuation in air pressure that uses a medium to propagate, reaches our eardrum, vibrates our eardrums and registers as sound in our brain

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What are the two types of waves in which sound can travel?

Longitudinal and transverse waves

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What two periods make up a single cycle of a sound wave?

A period of compression (increased pressure), followed by a period of rarefaction (decrease pressure)

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What is a zero crossing?

The centre line of zero amplitude in a sine wave that is reflected in DAWS

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DEF: reflection

Sound bouncing off a surface and returning in the direction from which it arrived

How does sound behave when reflected off a concave object?

Sound becomes more focused/stronger

How does sound behave when reflected off a convex surface?

It diffuses

How much is 0dB in Pa?

0.00002 Pa

If there is a doubling of power (Watts) what is the rule?

+3 dB m

If there is a halving of power (Watts), what is the rule?

-3 dB m

If there is a doubling in pressure (SPL), what is the rule?

+6 dB SPL

If there is a halving in pressure (SPL), what is the rule?

-6dB SPL

If there is a tenfold increase in power (Watts), what is the rule?

+10 dB m

If there is a tenfold decrease in power (Watts), what is the rule?

-10 dB m

If there is a tenfold increase in pressure (SPL), what is the rule?

+20 dB SPL

If there is a tenfold increase in pressure (SPL), what is the rule?

-20 dB SPL

What is the quantifier for Watts re: decibels?

dB m

What is the quantifier for pressure re: decibels?

dB SPL

Formula for determining ratio for power

dB m = 10 x log (p1/p2)

Formula for determining ratio for sound pressure

dB SPL = 20 x log (e1/e2)

DEF: Sound Pressure Level (SPL)

local pressure deviation from the ambient (average, or equilibrium) atmospheric pressure, caused by a sound wave

What is the standard international (SI) unit for sound pressure?

Pascal (Pa)

If only one value is given when determining dB ratio, what is the assumed other value?

0 dB

What type of scale is dB?

logarithmic

DEF: Envelope

The way a sound's amplitude changes over time

DEF: Attack

the beginning of the sound and the way it changes before it reaches its steady-state intensity

DEF: Decay

the rate at which a sound fades to silence

Formula for determining speed of sound at a given temperature?

c = 331 + 0.6 x t

DEF: Sustain

the steady state of a sound at its maximum intensity

What is the speed of sound at 0ºC?

331

DEF: amplitude

The amount of pressure being exerted on molecules in dB

what does RMS stand for?

Root Mean Squared

DEF: root mean squared (RMS)

a calculation of the average of values over a period of time to determine the average perceived loudness

What is the formula for calculating the length of a soundwave in meters?

λ = c / f

How do you determine the added frequencies that occur as a result of the combination and interaction of two sine waves?

calculate the sum of both and the difference of both

What is the formula for calculating phase shift in degrees?

Ø = Δt x 360 x f measured in miliseconds

What is the formula for calculating phase shift in cycles?

Ø = Δt x f

What is the makeup of a triangle wave?

A sine wave plus odd harmonics, increasing in frequency and decreasing in amplitude stacked on top of each other

What is the makeup of a square wave?

a sine wave with odd harmonics, but has more harmonics than the triangle wave

What is the makeup of a sawtooth wave?

a sine wave with odd and even harmonics above the fundamental

Comparatively, how do pink and white noise sound to us?

White noise sounds very bright because of the way our ears perceive sound. Pink noise sounds darker because there is more low end content

What does the fundamental tone determine?

pitch

How does a triangle wave sound?

sounds brighter than the sine wave because it contains higher frequencies as part of the sound rather than just the fundamental

How does a square wave sound?

brighter still than the triangle because it has more harmonics

How does a sawtooth wave sound?

brightest of all the basic wave shapes because it has the most harmonics; more nasal

Do sine waves start in or out of phase and by how much?

Sine waves start in phase

Do cosine waves start in or out of phase and by how much?

Cosine waves start 90º out of phase

DEF: phon

a unit of loudness measurement for pure tones

DEF: masking

when a sound is covered up by another, louder/more harmonically rich sound in the same frequency range

Why do sound waves travel faster in warmer temperatures?

The air molecules have more energy at a higher temperature and vibrate faster enabling sound waves to travel more quickly

What is a longitudinal wave?

A wave in which the displacements of a medium are in the direction of or directly opposite to the direction of prolongation of the wave

What is a transverse wave?

A wave where the displacements of a medium are at a right angle to the direction of propagation of a wave

what does the "m" in dBm stand for?

milliwatts

what is the equivalent to 0dBm in watts?

0.001 watts (1 milliwatt)

P = V^2 / R

``` R = resistance in ohms V= voltage in volts P= electric power in watts ```

What equation do you use when calculating the value in dBu against a given reference in watts ?

pressure | dBu = 20 x log (p1/p2)

What equation do you use when calculating the value in dBV against a given reference in volts ?

pressure | dBu = 20 x log (p1/p2)

What equation do you use when calculating the value in dBm against a given reference in volts ?

power | dBm = 10 x log (e1/e2)

What are weighting networks?

Ways of measuring decibels which account for the Fletcher Munsen curve.

A Freq. Weighting (incl. Phon line reference)

weighting network designed to reflect the response of human hearing, generally shown in dB(A). Has the most dramatic frequency response referenced to the 40 Phon line used between 20-55 dB SPL

B Freq. Weighting (incl. Phon line reference)

Used to weight things of moderate volume referenced to the 70 Phon line used between 55-85 dB SPL

C Freq. Weighting (incl. Phon line reference)

used for louder volumes, above 80 dB referenced to the 100 Phon line used about 85 dB SPL