dB(decibel), and so on…

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# dB(decibel), and so on… - PowerPoint PPT Presentation

dB(decibel), and so on…. … background for using digital audio editors Reference. 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, …).

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### dB(decibel), and so on…

… background for using digital audio editors

Reference

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.

The Logarithmic Scale

The log of a number a is the power to which you must raise 10 to get the number a.

Use dB to describe ratios
• Difference in decibels
• 3dB: twice the power
• 10dB: 10 times more
• 60dB:106 times more
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.

White noise:

a mix of all audible frequency

Experiment: how big is a decibel?
• 1dB is close to the Just Noticeable Difference
• sound levels are rarely given with decimal places.
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
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.
Loudness
• Loudness is a subjective (主觀的) 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
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

Record (VU meter)

Cut/paste/copy

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

Functions in Editors