Would someone please explain the dB system??

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satrne

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I know very little about decibels except that they are a way of measuring volume, and that they increase by exponentially (I think??) Could someone explain it to me in a way that it would be relevent to recording/mixing?? I am new to home recording (about half a year) and I really want to hone my mixing skills more than anything...

Tanks alot!!

Justin

p.s. To listen to stuff i've done, goto http://members.directvinternet.com/satrne/
 
Okay, lemme open it up. I've looked at those kinda techie articles about dB, and they never really helped me record better. So, here's my understanding:

1 Zero's the ceiling. When the meter indicates that the signal has gone above zero, it means you've got distortion if you're recording digitally.

2 Everything goes down from zero. -1 dB, -2 dB, -3 dB, and so on. One dB is the smallest change in loudness easily perceptible to most listeners. I can hear smaller differences than that sometimes, in relation to other tracks in the mix.

3 If you go down low enough, the signal gets so quiet that it disappears into and gets swallowed up by the noise floor, which is the unavoidable noise generated by the electronics of your gear. The idea is to get as low a noise floor as possible, so that it isn't very audible in your recordings.

4 Conventional wisdom says to record pretty close to zero, without clipping of course. But if you're recording at 24-bit or above, then it isn't as important. In fact, Sonusman recently talked about not being worried at all about hitting as close to zero as he can.

Okay, anything wrong with that?

Next question: anything else important I should know about dB that will actually help me get better recordings or mixes?
 
Ummm, quick cheat-sheet tips I can think of.....

+3db = twice as loud
+6db = 4 times as loud
+10db = 10 times as loud

-3db = 1/2 as loud
-6db = 1/4 as loud
-10db = 1/10 as loud
 
Uber,

It actually gets more complicated than that. As an engineer, the most important thing to me is the reference used, i.e. power (dBm), voltage (dBV). The "m" in dBm stands for a reference of 1 milliwatt. The "V" in dBV stands for 1 Volt.

When you represent a power signal in dBm you are expressing it's strength related to the reference (1 milliwatt) and use the follwing formula:

dBm = 10 log(P1/P2) p2 = 0.001 watt

Plugging in some numbers of your own will show you that 3 dB represents a doubling of power and -3dB represents cutting the power in half.

The formula used for dBV is:

dBV = 20Log (V1/V2) where V1 = 1 Volt

In this case 6 dB represents a doubling and -6dB means the signal has been cut in half.

People get in trouble when they use the term dB to describe a relative increase or decrease in signal but forget to tell each other what reference they are using.

Most of the time in audio you're safe assumming that db refers to a power measuement, but more and more I see manufactures specifying hardware using dBV.
 
I hesitated posting anything because it's easy to muddy up the water and get people more confused.

Actually, I think your approach to using DBs is right-on and is what most folks here should concentrate on. No one really cares how much power is contained a 37.22873645 dBm signal, all they want to know is approximately how much signal is lost/gained when attenuation/gain is expressed in dB.
 
I think many people don't understand when we are speaking of voltage, of power, and when it changes thru the chain, from the mic to the speakers. Things like power transfer vs. voltage transfer and stuff like that. Anyways, it always confused me and I think that if somebody can give a simple explanation to that, then it will be great.
Though I understand it better now, there are still things that I can't reason (like why you bridge impedances with mic and pres, but you match them with amps and speakers... please don't tell about power and voltage transfer, just tell me why one applies in one situation and the other in the others).

Cheers, Andrés
 
Just remember that dB by itself is only a RATIO, which allows you to compare two different volume levels to eachother, but doesn't have any actual specific value.

As Phyl said, it is only when you reference the dB to a constant that it becomes a specific unit of measurement. There are many reference options, and which one is being used is represented by a letter appended to the dB (like dBu or dBV).

Dobro's definition is just one kind of useage of dB that is specific to meters on digital gear (where zero represents maximum digital saturation before clipping, i.e. 1111111111111111 in a 16 bit system). But it is only one of many.

If I was an actual engineer like knightfly, barefoot, or sjj, I would actually know more about what I'm talking about!
 
There are 25 links to sites that explain decibels below.

decibels

Press the above word, to get to the 25 links.
 
you gotta admit that the power transfer vs. voltage transfer thing is pretty confusing. Didn't even audio gear makers took some decades until they switches from one way to the other?
 
I'm not sure what switch you're talking about...are you referring to the way they spec products?
 
UberGawkman said:
Ummm, quick cheat-sheet tips I can think of.....

+3db = twice as loud
+6db = 4 times as loud
+10db = 10 times as loud

-3db = 1/2 as loud
-6db = 1/4 as loud
-10db = 1/10 as loud
Click to expand...

It isn't how loud it gets, but how much more/less energy is used...

If the dB-SPL (sound preassure level) in a room is, say, 70 dB, and you raise it to 80 dB, you will need 10 times the energy, while you feel it is twice as loud...
 
Phyl said:
I'm not sure what switch you're talking about...are you referring to the way they spec products?
Click to expand...

I meant when they "switched", not switches. Sorry for the typo.

The thing is that at the beginning they did transfers with fixed resistance, then they forgot about that. So that's a hint that even the industry wasn't quite sure of what was the best procedure.

Of course maybe it was because of the legacy of the telephone industry. But it could be the lack of hindsight in an industry. Remember the guy who said that 640 kb should be enough for anybody?
 
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