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
