dB Flashcards
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
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
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: 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)
dBA
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)
dBB
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)
dBC
used for louder volumes, above 80 dB referenced to the 100 Phon line used about 85 dB SPL
DEF: dBW
The decibel watt or dBW is a unit for the measurement of the strength of a signal expressed in decibels relative to one watt.
What is the formula for power in dBW?
DEF: dBm
is unit of level used to indicate that a power ratio is expressed in decibels (dB) with reference to one milliwatt(mW)
What is the formula for dBm?
0dBu reference level in V?
0.775 V
What is the reference level for 0dBV in volts?
0dBV = 1 volt
Nominal operating level for professional standard equipment?
+4 dBu
1.2 V
Nominal operating level for consumer/semi-pro grade equipment?
- 10 dBV
0. 32 V
how do you calculate the voltage based on the reference value?
10(dB/20)x [0dB value]
What is the voltage for professional grade equipment (+4dBu) in v rms?
1.228 v rms
10(4/20) x 0.775 = 1.228 v rms
What is the voltage for consumer grade equipment (-10 dBV) in v rms?
0.316 v rms
10(-10/20) x 1 =0.316 v rms
0 dBm in watts?
0.001 W (1 mW)
How do decibels change with distance?
The sound intensity level decreases by half (of the initial value of sound intensity, -3dB) with doubling of distance.
Standard operating levels for hi-fi equipment?
- 10 dBu
0. 25 V
What is the standard operating level for broadcasting?
6-8 dBu
1.55 V - 1.95 V
DEF: dBV
a logarithmic voltage ratio with a reference to voltage of 1V
DEF: dBu
a logarithmic voltage ratio with a reference of 0.775 volts
DEF: dBFS
a unit of measurement for digital systems using a binary code where 0dBFS is assigned to the maximum possible digital level
What is the difference (in dB) between the semi-pro/consumer standard level (-10dB) and the professional standard level (+4dB)?
11.76 dB
