Decibel Scales and Meters: Newbeeeee question

[sgpatel]

I am confused about the decibel scale that is used on meters. I have been reading and trying to understand how meters work. I came up on a article where it was mentioned that 0db is the 'threshold of hearing' and then later in the same article it was mentioned that digital audio has a limit of 0db. This is what confuses me as to if 0db is the 'threshold of hearing' then how 0db be the maximum limit in digital audio. I apologize in advance for such a stupid question. Also the meter in wavelab and most meters display number like -48,-40,-32,-24,-16,-8, 0 db. Why are these negative if the threshold of hearing starts from 0db and upwards. . The article had the following chart:
0dB Threshold of hearing
20dB Quiet living room
50dB Average office
70dB Busy street
80dB Average factory
110dB Thunder
120dB Airport runway
133dB Threshold of pain

so then shouldnt the meters start from 0db,8db,16db etc....
Once again i do apologize since this might be very basic when it comes most board members.....any explanation would be helpful.....i have also posted this under the mixing and mastering forum topic.

[Dags]

Yo sgpatel

Going on my somewhat limited knowledge of such things, the 0dB referred to in digital recording is actually dBFS (Decibel Full Scale) - the point after which distortion starts occurring.

If we take 0DbFS as the loudest signal we can achieve without distortion in a digital signal path, then all other levels must be below that point, hence the negative numbers.

Someone out there with much more knowledge of such things may be able to clarify a bit better (and probably pick me up on where I have erred)

Dags

[Farview]

You are confusing all the different db scales. The chart that you refered to was measuring sound pressure: dbSPL. That is the measure of the sound around you, that you hear.
dbFS is what digital meters read. 0dbfs is the largest signal that can be communicated in the digital world. Everything else is a negative #.


dbVU is what the meters on your analog board read. Line level = 0dbVU = -12dbfs

db's are just a scale to measure power, until you know what the db is in reference to, you don't know what you are looking at.

[Ziller]

decibels measure the change in perceived loudness, something like a 1 bel is "twice as loud". So, you have to have a reference point for the scale. So, for the scale with threshold of pain, they (i think the phone co) set the reference point 0 as threshold of hearing, and measured off that. For digital, they (don't know who) set the reference point 0 as digi distortion, and measured off that (so it actually goes DOWN from the reference point). In a lot of electronic gear, the reference point 0 is set as 1 volt, and dBs are measured off that.

The confusing thing is there is no one scale. Pick any point as 0dB, and measure "twice as loud" from there.

[Farview]

6 db is twice as loud.

[ermghoti]

By definition, 10dB is twice as loud, +6dB is the result of doubling wattage/power.

[easychair]

6db is 4X power, not double. 6db is double the voltage.

[Farview]

[sarcasm]I wonder why noobs have such a hard time with this. It seems pretty straight forward.[/sarcasm]

[easychair]

Originally Posted by Farview

[sarcasm]I wonder why noobs have such a hard time with this. It seems pretty straight forward.[/sarcasm]

Plus it's posted in at least three places, so he has to remember where he posted it, and then go through three sets of confusing answers.