H - Decibels Flashcards
what is a decibel
a logarithmic unit used to express the ratio of two values of a physical quantity. it is 1/10th of a bell
what 2 values does a decibel require to have meaning
how much louder is one sound compared to another/ how much voltage a signal has compared to another
the dB scale describes the ratio of what 2 quantities
power (acoustic or electrical) and pressure (acoustic or electrical)
sound pressure level is…
the local pressure deviation from the ambient atmospheric pressure, caused by a sound wave
what is a logarithmic scale
a non-linear scale used when there is a large range of quantities
our perception of frequency and loudness is….
logarithmic
what is the base 10 logarithm
the number that 10 must be raised to the power of, in order to equal the number.
a bel is the log of an…..
electrical or acoustic power ratio
what is the dB suffix
the dB suffix defines the unit type, also defines the standard reference value.
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
what is dBm and its reference level
became the standard volume indicator and reference level in the 1940s. odBm = 0.001 watts (1 milliwatt)
what is dbV and its reference level
was used for many years for voltage reference. 0dbV = 1 volt RMS.
what is dbv and its reference level
the NAB adopted the use of the lower case v to denote the voltage value corrosponding to the power indicated by dBm (if one assumes a 600 ohm circuit). 0dBV = 0.775 Volts
what is dBu and its reference level
the dBu replaced the dBv, and is the more appropriate term for output or input voltage. 0dBu = 0.775 volts.
what is the nominal operating level for professional standard equipment….
+4dBu
what is the nominal operating level for consumer standard equipment….
-10dBV
what is the electric power definition
electric power is the rate of energy consumption in an electrical circuit
what is dBFS
decibels relative to full scale, used for amplitude levels in digital systems. 0dBFS is assigned to the maximum level,
what does a digital systems dynamic range mean
the ratio between the maximum signal level and the noise floor.
bit depth means
the maximum digital level that can be encoded in a digital system determined by the number of bits
what does full scale mean
the maximum possible value in the positive direction in a PCM digital system
what is digital clipping
it is a form of distortion when an amplifier or audio signal is driven beyond its maximum capacity.
What is the threshold of pain?
approx. 130 dB
How loud is normal conversation?
Approx 60 dB
How much is 0dB in Pa?
0.00002 Pa
what is sound pressure level measured in?
Pascals
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 decrase 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
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
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
DEF: phon
a unit of loudness measurement for pure tones
what does the “m” in dBm stand for?
milliwatts
what is the equivalent to 0dBm in watts?
0.001 watts (1 milliwatt)
what is the threshold of human hearing
o dbSPL
what is o dBSPL in pascals
0.00002 pascals
what level will result in a perforated ear drum
160 dB SPL
how many pascals is 160dB SPL
2000 Pa
in a 16-bit system, what is the maximum possible positive level
32767
2 to the power of 16 / 2
how many samples do people tend to settle on over the maximum level when audible clipping occurs
2 or 3
