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

2. jmchen, Fall 20072 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.

3. jmchen, Fall 20073 The Logarithmic Scale The log of a number a is the power to which you must raise 10 to get the number a.

4. jmchen, Fall 20074 Use dB to describe ratios Difference in decibels –3dB: twice the power –10dB: 10 times more –60dB:10 6 times more

5. jmchen, Fall 20075 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. 3dB refers to twice the power and times the sound pressure

6. jmchen, Fall 20076 Experiment: how big is a decibel? 1dB is close to the Just Noticeable Difference sound levels are rarely given with decimal places. White noise: a mix of all audible frequency

7. jmchen, Fall 20077 Standard Reference Level (1/2) For sound intensity, the reference level (for air) is 20 micropascals (0.02mPa) –1 pascal = 1N/m 2 This is about the limit of sensitivity of the human air, in its most sensitive range of frequency Ex: sound pressure level of 86dB

8. jmchen, Fall 20078 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.

9. jmchen, Fall 20079 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

10. jmchen, Fall 200710

11. jmchen, Fall 200711 Equal Loudness Curve Also known as Fletcher-Munson curve at 1kHz, phon=dB 1 sone 2 sones

12. jmchen, Fall 200712 Experiment (ref)ref Experiment set up interpretation

13. jmchen, Fall 200713 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

14. jmchen, Fall 200714 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