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Help with calculation

April 15, 2013 | 10:07 am

Hello everyone .
How do I understanding this explanation in grey box.

It says the amplitude of a sinusoidal tone decreased by half (6 dB) in 5 milliseconds.I want know how come half=6db in example.
I can only see the tone decreased by 1/8(0.125) in 5ms.Not as half.
And an eightfold (18 dB) increase in 5 ms creates a percussive effect. I do not understanding why eightfold = 15db . I want know where is come from?

Can somebody teach me understanding this example ? and What do I have to understanding first for this ?

Thanks in advance.

Lu

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April 15, 2013 | 11:41 am

http://en.wikipedia.org/wiki/Decibel

look at the scale to the right – you’ll see -6dB equals roughly halving the amplitude.
in Max you can look at [atodb], [live.gain~] and others.


April 15, 2013 | 12:53 pm

Hello Dear.

Thanks for your reply. But Unfortunately I don’t get anything out of it.
I’ve look up wiki and that’s hurt.I do not understanding most sentence.
Maybe my question is not what I mean to be.
Let’s make a simple.
half means (1/2) . simply ,we can divide into 1 .
-Half(6) in this example . the whole will be 12. At this point I don’t see any 12 value in example.
-What I know eightfold is equal to 8 times. so how come eightfold =18 in this example.
This is my perception of look at the example.Please help to switch my perception to understand this things.
Forgive me not having strong math foundation .

many thanks.

Lu


April 15, 2013 | 1:39 pm

Decibels are not a linear scale. Imagine you have a fader on a mixing board, and you move that fader from the ’0′ position, to the ‘-6′ position. The psychoacoustic (how it sounds to the listener) level of the audio playing through that fader is now ‘half’ of what it sounded like before. Move it down another 6 decibels, you’re at -12. But you’re now at ‘half’ the volume you were at at -6 (a total of a quarter of the volume you were at at 0). -18 is another decrease by half – half of a half of a half, which is 1/8th.

However, if you wanted to get 1/8th the volume level in Max, using the *~ object (which uses LINEAR numbers, unlike the decibel scale), you’d put in .125 to get it to 1/8th the original input volume.


April 15, 2013 | 1:47 pm

Hmm, seems I was incorrect. It appears to be generally accepted that:

3db = doubling of ‘power’
6db = doubling of waveform amplitude
10db = doubling of perceived volume (which is highly subjective).


April 17, 2013 | 4:21 pm

Hello Dear

The Key point was Decibels are not a linear scale.

I am still full did not get that. but I know the definition.and it big picture will come to me.

Thanks.

Lu


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