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Term 1 Theory Prep > dB > Flashcards

dB Flashcards

1
Q

What is a decibel?

A

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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2
Q

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

A

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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3
Q

How much is 0dB in Pa?

A

0.00002 Pa

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4
Q

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

A

+3 dB m

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5
Q

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

A

-3 dB m

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6
Q

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

A

+6 dB SPL

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7
Q

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

A

-6dB SPL

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8
Q

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

A

+10 dB m

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9
Q

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

A

-10 dB m

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10
Q

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

A

+20 dB SPL

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11
Q

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

A

-20 dB SPL

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12
Q

What is the quantifier for Watts re: decibels?

A

dB m

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13
Q

What is the quantifier for pressure re: decibels?

A

dB SPL

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14
Q

Formula for determining ratio for power

A

dB m = 10 x log (p1/p2)

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15
Q

Formula for determining ratio for sound pressure

A

dB SPL = 20 x log (e1/e2)

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16
Q

DEF: Sound Pressure Level (SPL)

A

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

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17
Q

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

A

Pascal (Pa)

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18
Q

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

A

0 dB

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19
Q

What type of scale is dB?

A

logarithmic

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20
Q

DEF: phon

A

a unit of loudness measurement for pure tones

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21
Q

DEF: masking

A

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

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22
Q

Why do sound waves travel faster in warmer temperatures?

A

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

23
Q

What is a longitudinal wave?

A

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

24
Q

What is a transverse wave?

A

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

25
Q

what does the “m” in dBm stand for?

A

milliwatts

26
Q

what is the equivalent to 0dBm in watts?

A

0.001 watts (1 milliwatt)

27
Q

P = V^2 / R

A

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

28
Q

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

A

pressure dBu = 20 x log (p1/p2)

29
Q

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

A

pressure dBu = 20 x log (p1/p2)

30
Q

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

A

power dBm = 10 x log (e1/e2)

31
Q

What are weighting networks?

A

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

32
Q

A Freq. Weighting (incl. Phon line reference)

dBA

A

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

33
Q

B Freq. Weighting (incl. Phon line reference)

dBB

A

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

34
Q

C Freq. Weighting (incl. Phon line reference)

dBC

A

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

35
Q

DEF: dBW

A

The decibel watt or dBW is a unit for the measurement of the strength of a signal expressed in decibels relative to one watt.

36
Q

What is the formula for power in dBW?

A
37
Q

DEF: dBm

A

is unit of level used to indicate that a power ratio is expressed in decibels (dB) with reference to one milliwatt(mW)

38
Q

What is the formula for dBm?

A
39
Q

0dBu reference level in V?

A

0.775 V

40
Q

What is the reference level for 0dBV in volts?

A

0dBV = 1 volt

41
Q

Nominal operating level for professional standard equipment?

A

+4 dBu

1.2 V

42
Q

Nominal operating level for consumer/semi-pro grade equipment?

A
  • 10 dBV
    0. 32 V
43
Q

how do you calculate the voltage based on the reference value?

A

10(dB/20)x [0dB value]

44
Q

What is the voltage for professional grade equipment (+4dBu) in v rms?

A

1.228 v rms

10(4/20) x 0.775 = 1.228 v rms

45
Q

What is the voltage for consumer grade equipment (-10 dBV) in v rms?

A

0.316 v rms

10(-10/20) x 1 =0.316 v rms

46
Q

0 dBm in watts?

A

0.001 W (1 mW)

47
Q

How do decibels change with distance?

A

The sound intensity level decreases by half (of the initial value of sound intensity, -3dB) with doubling of distance.

48
Q

Standard operating levels for hi-fi equipment?

A
  • 10 dBu
    0. 25 V
49
Q

What is the standard operating level for broadcasting?

A

6-8 dBu

1.55 V - 1.95 V

50
Q

DEF: dBV

A

a logarithmic voltage ratio with a reference to voltage of 1V

51
Q

DEF: dBu

A

a logarithmic voltage ratio with a reference of 0.775 volts

52
Q

DEF: dBFS

A

a unit of measurement for digital systems using a binary code where 0dBFS is assigned to the maximum possible digital level

53
Q

What is the difference (in dB) between the semi-pro/consumer standard level (-10dB) and the professional standard level (+4dB)?

A

11.76 dB

Term 1 Theory Prep (11 decks)

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