dBdecibel, and so on

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dB(decibel), and so on

• background for using digital audio editors
• Reference

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Definitions

• The decibel (dB) is used to measure sound level
• dB is a logarithmic unit used to describe a ratio
  (of power, sound pressure, intensity, )

Wikipedia A decibel is one tenth of a bel (B).
Devised by engineers of the Bell Telephone
Laboratory to quantify the reduction in audio
level over a 1 mile length of standard telephone
cable, the bel was originally called the
transmission unit or TU, but was renamed in 1923
in honor of the Bell System's founder and
telecommunications pioneer Alexander Graham Bell.
In many situations, however, the bel proved
inconveniently large, so the decibel has become
more common.
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The Logarithmic Scale
The log of a number a is the power to which you
must raise 10 to get the number a.
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Use dB to describe ratios

• Difference in decibels
• 3dB twice the power
• 10dB 10 times more
• 60dB106 times more

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Sound Pressure

• Microphone responds proportionally to sound
  pressure, p
• The power in a sound wave, all else equal (same
  frequency), goes as the square of the pressure.

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Experiment how big is a decibel?
White noise a mix of all audible frequency

• 1dB is close to the Just Noticeable Difference
• sound levels are rarely given with decimal places.

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Standard Reference Level (1/2)

• For sound intensity, the reference level (for
  air) is 20 micropascals (0.02mPa)
• 1 pascal 1N/m2
• This is about the limit of sensitivity of the
  human air, in its most sensitive range of
  frequency
• Ex sound pressure level of 86dB

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Sound Pressure Level (2/2)

• 0dB does not mean no sound
• Not all sound pressure are equally loud.
• Human ear does not respond equally to all
  frequency (we are much more sensitive to sound in
  1kHz to 4kHz)
• Sound meters are usually fitted with a filter (A
  weighting factor) whose frequency response is
  like that of the human ear. The measure result is
  called dBA.

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Loudness

• Loudness is a subjective (???) measure of the
  sound pressure, measured by sone
• One sone is equivalent to 40 phons
• Of a 1kHz tone phon is the same as dB
• Other frequency refer to the frequency response
  of human ear.
• 10 dB increase in sound level corresponds to a
  perceived doubling of loudness

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(No Transcript)
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Equal Loudness Curve
Also known as Fletcher-Munson curve
at 1kHz, phondB
2 sones
1 sone
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Experiment (ref)
Experiment set up interpretation
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Intensity, radiation and dB

• Isotropic source, far from any reflecting
  surfaces
• Intensity I the power per unit area
• Double the distance, intensity reduce by 4, sound
  level reduced by 6 dB

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Functions in Editors

• Record (VU meter)
• Cut/paste/copy
• Pitch adjustment
• Reverb/flanger/echo
• Mechanize
• Vocal removal
• Resampling
• Cue points
• Hiss removal
• Pop removal

• You may find (some of) these in Goldwave (and
  Cakewalk)
• You are free to choose either one
• Cakewalk works with wav only
• Cakewalk seems to have a better pitch shifter