Decibel Theory........... Grr. (1 Viewer)

[ClockworkSoldier]

Can anyone explain the maths associated with the Decibel Theory in laymen terms?

I know stuff Like...

1mW = dBm
1v=dBv
0.775v = dBu
0.00002Pa = dBSPL

Power = 10log. Watts/Pa = 20 log
References:
1 Mw = dBm
1 v = dBv
1 u = 0.775
0.00002 Pa.

Anti log: Divide front number and resulting number each by 10. eg. 10/10 = 1 (Cancels). 6/10 = 0.6.
-----------------------------------------------------------------------------------------------------------------
These are a couple of example questions that I have been given:

1) The recommended mixing level is around 90dB SPL. What is that in Pascal?

2) A line amplifier has a gain of 37dB. With an input of 0.2V, what is the output voltage?

3) The output of a microphone is around 0.5mV. What is the gain needed on the pre-amp to
bring it to +4dBu?

Any help whatsoever will be greatly appreciated. I really need to understand the concepts, but can't seem to get my head around them.

 

[jb_nc]

try wikipedia

 

[withoutaface]

Can anyone explain the maths associated with the Decibel Theory in laymen terms?

I know stuff Like...

1mW = dBm
1v=dBv
0.775v = dBu
0.00002Pa = dBSPL

Power = 10log. Watts/Pa = 20 log
References:
1 Mw = dBm
1 v = dBv
1 u = 0.775
0.00002 Pa.

Anti log: Divide front number and resulting number each by 10. eg. 10/10 = 1 (Cancels). 6/10 = 0.6.
-----------------------------------------------------------------------------------------------------------------
These are a couple of example questions that I have been given:

1) The recommended mixing level is around 90dB SPL. What is that in Pascal?

2) A line amplifier has a gain of 37dB. With an input of 0.2V, what is the output voltage?

3) The output of a microphone is around 0.5mV. What is the gain needed on the pre-amp to
bring it to +4dBu?

Any help whatsoever will be greatly appreciated. I really need to understand the concepts, but can't seem to get my head around them.

B Mantello @ Sublime U?

 

[ClockworkSoldier]

B Mantello @ Sublime U?

Ahem...

???

 

[goony]

Off the top of my head, Gain = output voltage / input voltage ... or Vo/Vi

This is in units of V/V though. For decibels (in electrical circuits) you'd want something like Gain = 20log(Vo/Vi)

 

[ClockworkSoldier]

I got it. Thanks guys.

A couple of the answers for the questions on the sheet:

20 log (NEW/REF) = ____
20 log (5.7v/0.775) = ___
20 log (7.35)
20 x 0.87
= 17.3 dBu.

20 log (NEW/REF) = ___
20 x log (1.5/5v = 0.3)
20 x -52.3
= -10.4dB

10 log (NEW/REF) = 18dB REF = 12mW
log (x/12mW) = 1/10 = 1.8
= (x/12mW) = 10^1.8
x = 12mW x 63.1 =
x = 757.15mW

They seem out of context, but I typed them mainly for my own benefit. Lol.