I'm only young...

[android]

I've just received my copy of AoE 3rd edition (it was a gift, honest) and I'm learning fast. After reading about decibels on page 15 (specifically footnote 19) ...

I'm only 17.5 dBY, so can someone give me an oscilloscope? 

[codeboy2k]

I've just received my copy of AoE 3rd edition (it was a gift, honest) and I'm learning fast. After reading about decibels on page 15 (specifically footnote 19) ...

I'm only 17.5 dBY, so can someone give me an oscilloscope? 

No scope for you! Get out ! 

You don't get decibels yet.  It needs to be a ratio, relative to something else. So if your average life expectancy is 78.7 years, let's call that a Full Life (FL), and you are 17.5 years, then you are going to be



or 13dB below a full life You have plenty of time !

So keep reading ... it's a great book to own.

(PS: if you don't get the "get out" reference, then search the Soup Nazi)

[EEVblog]

You don't get decibels yet.  It needs to be a ratio, relative to something else. So if your average life expectancy is 78.7 years, let's call that a Full Life (FL), and you are 17.5 years, then you are going to be

Careful, you'll start a war over whether to use 20 Log or 10 Log there 

[MatthewEveritt]

You don't get decibels yet.  It needs to be a ratio, relative to something else. So if your average life expectancy is 78.7 years, let's call that a Full Life (FL), and you are 17.5 years, then you are going to be

Careful, you'll start a war over whether to use 20 Log or 10 Log there 

You have no idea how incensed I am right now.

On a minusculy  more serious note, 17.5 dBY (relative to one year) would make android either 7.5 or 56 years old, not 17.5

[onlooker]

Careful, you'll start a war over whether to use 20 Log or 10 Log there 

It all depends on if his years are powerful or powerless.

[Howardlong]

I don't think most people really "get" the dB properly until they use it practically and reasoanbly often. Without the practical use of dB it will remain a difficult concept to grasp, focussing too much on calculating backwards and forwards between dB and absolute units, rather than using and thinking in dB directly, at least that has been my experience particularly from an RF perspective.

[MatthewEveritt]

I don't think most people really "get" the dB properly until they use it practically and reasoanbly often. Without the practical use of dB it will remain a difficult concept to grasp, focussing too much on calculating backwards and forwards between dB and absolute units, rather than using and thinking in dB directly, at least that has been my experience particularly from an RF perspective.

Agreed, although a good understanding of the maths is pretty important too. Once you know what the dB is actually doing it becomes hugely more useful. If only I could remember how it was explained to me the first time!

Just don't get me started on 'antilog'... 

[TimFox]

If you use dB to compare two sums of money (denominated in dollars or other currency), be sure to use the factor 10, not 20, because money is power.

[android]

Oops...I forgot to mention my ratio reference which was indeed 1 (earth) year.

I propose that dBY henceforth becomes a new standard of age relative to 1 year. This would make the age of the universe a much more manageable 71.37 ... small enough to fit on an LCD 

I wonder who can claim to be the oldest (and youngest) forum member...in dBY? There can't be many of us over 20.

[TimFox]

As linear transformations for my old age:
At 32, I started converting my age to Celsius.
At 40, I started converting to degrees Réaumur.
A few year ago, I started converting to radians.

[codeboy2k]

Careful, you'll start a war over whether to use 20 Log or 10 Log there 

I hate war   A Bel is a power ratio, it always has been.  The bastardization of the Bel in a voltage ratio and even a current ratio has caused the 20 log confusion. I'm going to stick with my choice of 20 log here because that's how voltages (and currents) are done, and I was trying to think it through as if the person's current age could be considered as a potential difference between his birth age and his death age, like a voltage is from GND to some full-scale voltage. So I decided it would be more similar to a  voltage, and not a power -- thus 20 log...

As a review for the young players .. the 20 log part comes into play when comparing output and input voltages;  the voltage is squared when converting from a power (as others have said). Here's the derivation (you could also use P = I²R for comparing output to input currents.

[SL4P]

But doesn't his height come into play?   

[Howardlong]

As a review for the young players .. the 20 log part comes into play when comparing output and input voltages;  the voltage is squared when converting from a power (as others have said). Here's the derivation (you could also use P = I²R for comparing output to input currents.

Somehow, I am not sure how much that's going to help many of the the young players!

[LabSpokane]

As a review for the young players .. the 20 log part comes into play when comparing output and input voltages;  the voltage is squared when converting from a power (as others have said). Here's the derivation (you could also use P = I²R for comparing output to input currents.

Somehow, I am not sure how much that's going to help many of the the young players!

Why not?  That's the definition and about as simple as it gets.

[codeboy2k]

Oops...I forgot to mention my ratio reference which was indeed 1 (earth) year.

I assumed you made a mistake and were actually 17.5 years old since you said you were young...
However, if you did the math right and you are indeed 17.5 dBY (relative to 1 year) then Matthew is correct...

On a minusculy  more serious note, 17.5 dBY (relative to one year) would make android either 7.5 or 56 years old, not 17.5

so you are either 7.5 or 56 years old



You're older than me, using the 10 log form . I'm just 17 dBY ...

[TimFox]

Yes, the Bel, and therefore the deciBel (dB) are defined as power ratios.
As a calculation aid, assuming that the impedance at both measurements is the same, the factor of 20 can be used to calculate that ratio in dB, since P = V^2/R and log(V^2) = 2 log (V).
Where this gets really tricky to keep track is in optoelectronics, where the output current of a photosensor is proportional to the optical power incident on the sensor.  Therefore, if you attenuate the optical power by 3 dB, you must increase the gain of the amplifier after the sensor by 6 dB to get the same output.