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Here are some interesting numbers, collected from a variety of sources, that help one to understand the volume levels of various sources and how they can affect our hearing.

Environmental Noise
Weakest sound heard	0dB
Whisper Quiet Library	30dB
Normal conversation (3-5')	60-70dB
Telephone dial tone	80dB
City Traffic (inside car)	85dB
Train whistle at 500', Truck Traffic	90dB
Subway train at 200'	95dB
Level at which sustained exposure may result in hearing loss	90 - 95dB
Power mower at 3'	107dB
Snowmobile, Motorcycle	100dB
Power saw at 3'	110dB
Sandblasting, Loud Rock Concert	115dB
Pain begins	125dB
Pneumatic riveter at 4'	125dB
Even short term exposure can cause permanent damage - Loudest recommended exposure WITH hearing protection	140dB
Jet engine at 100', Gun Blast	140dB
Death of hearing tissue	180dB
Loudest sound possible	194dB

 

OSHA Daily Permissible Noise Level Exposure
Hours per day	Sound level
8	90dB
6	92dB
4	95dB
3	97dB
2	100dB
1.5	102dB
1	105dB
.5	110dB
.25 or less	115dB

 

Perceptions of Increases in Decibel Level
Imperceptible Change	1dB
Barely Perceptible Change	3dB
Clearly Noticeable Change	5dB
About Twice as Loud	10dB
About Four Times as Loud	20dB

 

Sound Levels of Music
Normal piano practice	60 -70dB
Fortissimo Singer, 3'	70dB
Chamber music, small auditorium	75 - 85dB
Piano Fortissimo	84 - 103dB
Violin	82 - 92dB
Cello	85 -111dB
Oboe	95-112dB
Flute	92 -103dB
Piccolo	90 -106dB
Clarinet	85 - 114dB
French horn	90 - 106dB
Trombone	85 - 114dB
Tympani & bass drum	106dB
Walkman on 5/10	94dB
Symphonic music peak	120 - 137dB
Amplifier rock, 4-6'	120dB
Rock music peak	150dB

NOTES:

• One-third of the total power of a 75-piece orchestra comes from the bass drum.
• High frequency sounds of 2-4,000 Hz are the most damaging. The uppermost octave of the piccolo is 2,048-4,096 Hz.
• Aging causes gradual hearing loss, mostly in the high frequencies.
• Speech reception is not seriously impaired until there is about 30 dB loss; by that time severe damage may have occurred.
• Hypertension and various psychological difficulties can be related to noise exposure.
• The incidence of hearing loss in classical musicians has been estimated at 4-43%, in rock musicians 13-30%.

Statistics for the Decibel (Loudness) Comparison Chart were taken from a study by Marshall Chasin , M.Sc., Aud(C), FAAA, Centre for Human Performance & Health, Ontario, Canada. There were some conflicting readings and, in many cases, authors did not specify at what distance the readings were taken or what the musician was actually playing. In general, when there were several readings, the higher one was chosen.

There's a misunderstanding of what a dB is and what it measures. Here's a definition from Sweetwater's word for the day archive:

• A decibel (named for Alexander Graham Bell) is a tenth of a bel, and is used as an expression of power. Here's where the confusion arises: A decibel isn't a measure of ANYTHING; it is a ratio of two power levels. Because of the way our ears perceive volume, these ratios follow a logarithmic curve, expressing them as a decibel keeps things easier to deal with. Here are a few convenient decibel figures worth remembering: One decibel is commonly taken as the smallest volume change the human ear can reasonably detect. Doubling the POWER of an amplifier results in a 3 dB increase, which is a "noticeable" volume increase. Doubling the VOLUME of a sound is a 6 dB increase (you may occasionally see 10 dB listed as the "double-volume" figure, 6 dB is the more mathematically correct number). By doing the math, you can see that truly doubling your volume actually requires 4 times the amplifier power! Keep these figures in mind the next time you are comparing the specs of two pieces of equipment...
  
  Decibels are used all over the place in audio measurements and specifications partly because it is very easy to express extremely large or small values with decibels due to their logarithmic nature. The full depth of the topic is well beyond the scope of this writing, but suffice to say that the decibel always refers to a ratio of two values. It is never an absolute value. Thus when we speak of losses and gains in audio we use dB to quantify those values. If a signal goes into a unit and is output at a lower level it is said to be down by some value of dB. Decibels come in many variants: dB PWL, dB SPL (also known as Sound Pressure Level), dBm, dBu, dBV, dBv, and more.

The +/- 12 dB slider in WinAmp is a representation of dBV. Volume is measured in the air as dB SPL. The -80 to zero dB scale you referred to is dBFS (dB Full Scale). Because a dB is a ratio, and not an absolute unit of measure, it can be used to measure voltages or sound pressure levels in any number of different ways.



Without knowing what you are using as an output device (headphones, speakers, an amplifier with huge speakers attached, etc.) there is no way the software could know what SPL level you are producing, or that the MP3 player could know when you've exceeded a safe threshold (although it could make certain assumptions since most people listen to MP3 players with earbud-style headphones).

There's no way to use your webcam mic to measure SPL. You'll need an SPL meter with a built-in microphone or a calibrated mic that outputs a known voltage at a certain SPL.

dB FS is a measurement of the level of a "word" in digital audio. A "digital word" is a string of either 1's and 0's (usually 16 or 24 of them) which define a sampled sound's volume at a moment in time. Dealing with 16-bit audio, specifically, there is a theoretical maximum range of 96dB.

A -96 dBFS word would be 16 zeros, the smallest value a 16-bit word can represent:
0000000000000000

a 0 dBFS word would be 16 ones, the largest value a 16-bit word can represent:
1111111111111111