Module 6: The Decibel Flashcards
decibel (dB)
the most frequently used unit of measurement in hearing science. It is a unit related to physical power.
a logarithmic unit of the ration of two powers; one tenth of a bel, defined as
L =10 x log(P2/P1) ****
where P2 and P1 are respective powers.
one tenth of a Bel
doesn’t measure a physical property but a RELATIVE DIFFERENCE between two powers as a %.
When a value is expressed in dB, the measured property is called a LEVEL
relative difference
the ration of two quantities
- tells us HOW MANY TIMES greater one measurement is than another
- involves division
- example: Mississippi is twice as large as West Virginia.
Absolute difference
an amount by which one quantity is larger than another one.
- tells us how much greater one measurement is than another
- involves subtraction
- example: my son has grown 4 inch in the last month.
relative measurement
measurements involving relative differences
(e.g., the ratio, a division) between two quantities.
Humans do not respond accurately to absolute changes in physical properties. It’s easy to notice a difference from 1kg to 2kg (100% change) but not so easy to notice change from 101 Kg to 102 kg (1%) change.
absolute measurement
measurement involving absolute differences (e.g., subtraction) between two quantities.
octave
a relative unit of frequency in which one octave represents a doubling in frequency.
Bel (B)
a logarithmic unit of power equal to the logarithm base 10 of the ratio of two powers such that the level in bels is equal to log10(P2/P1), where P1 and P2 are respective powers.
it was developed to subscribe power loss along cables that transmitted speech signals.
Loudness vs Intensity
Loudness- the property of sound that allows
sounds to be ordered on a scale
extending from quiet (soft) to loud:
loudness depends mainly on the
intensity of sound.
human perception
Intensity-the measurable amount of property
such as force, rightness, (sound)
or a magnetic field.
how a machine would measure sound
sound pressure level
SPL
a logarithmic measure of the ratio of a specific sound pressure (P2) and a reference sound pressure of 20 uPa and expressed in decibels as
SPL = 20 X log (P2/20uPa)
sound intensity level
IL
a logarithmic measure of the ratio of a specific sound intensity (I2) to a reference sound intensity of 10 to the -12 W/m2 and expressed in decibels as
IL= 10 x log(I2/10 to the -12 W/m2)
hearing level
HL
a logarithmic measure (expressed in dB HL) of the ratio of sound pressure in reference to the audiometric zero level.
sensation level
(SL)
a logarithmic measure, expressed in dB SL, of the ratio of the actual sound pressure to the threshold of hearing of the listener.
persons own hearing reference
Relationship between Sound pressure levels and sound intensity
I : P squared
reference point/ reference level
a sound pressure of 20 uPa results from a sound intensity of 10 to the -12 W?m2
the value used as a reference magnitude in a ratio scale; the zero point of a relative scale.
the standard reference point for sound pressure is 20uPa. this sound pressure is equal roughly to the lowest sound pressure that can be heard by the human ear in mid frequency range.
the standard reference point for sound intensity is 10 to the -12 W/m2
0 dB ?
Zero level
equal to the reference point.
Does NOT mean absence of sound
Often called zero level
