The scientific “unit” we call the decibel • Hacker News Board

Re: The scientific “unit” we call the decibel

#121

Post by Ekaros » Thu, May 22, 2025, 9:34 AM UTC

kqr wrote: post #115

Ekaros wrote: post #110

Earlier quoted context omitted.

Well 10 millimetres of rain is different that 10 millimetres thickness for say branch...

At first I was going to contradict you but then I realised 10 mm of rain is actually a measure of volume or mass, corresponding to 10 kg, right? And of course, people use it mainly as a rate, i.e. 10 kg per hour, or per four hours, or six hours, or 24 hours. And it gets worse when we start talking about snow, the density of which can vary a lot!

Well depending on area you are counting it on. So yes per square meter it would be 10 kg. Your rain gauge might for example not have 10mm spaced markings...

Re: The scientific “unit” we call the decibel

#122

Post by jpc0 » Thu, May 22, 2025, 9:37 AM UTC

cousin_it wrote: post #82

Yeah. And don't get me started on the folks who think "6dB/octave" is a reasonable thing to say. Which is, apparently, everyone who works with audio filters except me.

How else would you describe what occurs other than 6dB/octave?

Re: The scientific “unit” we call the decibel

#123

Post by pajko » Thu, May 22, 2025, 9:41 AM UTC

Loudness is not measured in dB, but in phon (https://en.wikipedia.org/wiki/Phon) or sone (https://en.wikipedia.org/wiki/Sone).

Re: The scientific “unit” we call the decibel

#124

Post by margalabargala » Thu, May 22, 2025, 9:48 AM UTC

mikewarot wrote: post #68

rocqua wrote: post #51

Earlier quoted context omitted.

Decibels in gain, those are fine. Though they use a silly base. dBm makes a decent amount of sense, given the RF background. The fact that decibels work differently for voltage and power is very weird, but understandable in isolation. But audio decibels are horribly underspecified. And any other use of a decibel as a dimensionful unit is horrible. I think the RF people know, and that's why they use dBm. Any system th…

Decibels aren't units... they are ratios. The ratio could be gain, or loss, or compared to the noise floor, or the signal of interest, or a standard unit, such as Watts, milliWatts, or microVolts into 50 ohms. >The fact that decibels work differently for voltage and power is very weird, but understandable in isolation. If you have a given load, increasing the voltage by a ratio of 10:1 (20 dB) is exactly the same as…

> If you have a given load, increasing the voltage by a ratio of 10:1 (20 dB) is exactly the same as increasing the power by a ratio of 100:1 (20 dB) (because increasing the voltage ALSO increases the current, and the power is the product of the two)

It's not that we don't understand this. We do understand this, and simply think it's ludicrous that the same nominal "unit" is used to refer to both, rather than calling the voltage one, say, "hemidecibels". Because we're not talking about power always, we're talking about, as you say, ratios.

Re: The scientific “unit” we call the decibel

#125

Post by margalabargala » Thu, May 22, 2025, 9:53 AM UTC

Ekaros wrote: post #110

dns_snek wrote: post #106

Earlier quoted context omitted.

You haven't addressed any points the author has made, we don't need to have "experience" in a field to know that ambiguous units are ridiculous and bad. When I'm buying a piece of string for my garden, I don't need to find an agricultural textbook to know whether "10 meters" in agriculture is the same as "10 meters" in engineering, and whether the definition of "meters" depends on whether the string is made out of co…

Well 10 millimetres of rain is different that 10 millimetres thickness for say branch...

Could you elaborate on this?

If 10mm rain falls, and you have an open collection container, then the depth of the water in that container would be more, less, or the same as the thickness of the branch?

Re: The scientific “unit” we call the decibel

#126

Post by dubcanada » Thu, May 22, 2025, 9:54 AM UTC

pajko wrote: post #123

Loudness is not measured in dB, but in phon ( https://en.wikipedia.org/wiki/Phon ) or sone ( https://en.wikipedia.org/wiki/Sone ).

Tell that to everyone on the planet who uses dB

Re: The scientific “unit” we call the decibel

#127

Post by cesaref » Thu, May 22, 2025, 9:54 AM UTC

Generally speaking, the db scale is very useful for many practical situations, and this is overlooked in this critique.

As have been pointed out, it's just a power ratio on a logarithmic scale, but this has many benefits, the main one being that chaining gain/attenuation in a system is just a case of adding the db values together. 'We're loosing 4db in this cable, and the gain through this amp is 6db, so the output is 2db hotter than the input'. Talk to any sound engineer and you'll do this sort of thing successfully without necessarily understanding the science, so that's a massive win.

Re: The scientific “unit” we call the decibel

#128

Post by margalabargala » Thu, May 22, 2025, 9:58 AM UTC

hashhar wrote: post #100

lifthrasiir wrote: post #40

The only thing you should know is that any use of bel and thus decibel should ideally have the reference level suffixed (usually in parentheses or subscript), not implied. The absolute sound pressure level is dB(SPL). The human-perceived loudness level is dB(A) and similar. The RMS voltage expressed in power is dB(u) (formerly dB(v), not same as capital dB(V)). And so on. And then each different instance of dB unit i…

This is exactly it. The people who get confused by decibels are treating it a unit in it's own right when it's really just a ratio of some unit.

Disagree.

The people who get confused by decibels, are exposed to other people treating it like it's a unit in its own right.

I agree that what the parent described, should be done. If it was what was done, this article wouldn't exist.

Re: The scientific “unit” we call the decibel

#129

Post by [deleted] » Thu, May 22, 2025, 10:02 AM UTC

neepi wrote: post #60

fouronnes3 wrote: post #53

Earlier quoted context omitted.

However you must concede that the perspective of an outsider can be refreshingly eye opening sometimes, even to experts. Especially when it reveals the arcane practices that make a field difficult to learn - for example here the point about the base being too implicit is very valid. The article is perhaps ignorant of a few things, but its criticism shouldn't be dismissed outright IMO. Accepting constructive criticism…

That would assume that the entire world hasn't already tried this a thousand times over. Measurements are standardised communication tools. If you start changing the definitions, things fall out of the sky and on your head.

[deleted]

Re: The scientific “unit” we call the decibel

#130

Post by lifthrasiir » Thu, May 22, 2025, 10:03 AM UTC

margalabargala wrote: post #128

hashhar wrote: post #100

Earlier quoted context omitted.

This is exactly it. The people who get confused by decibels are treating it a unit in it's own right when it's really just a ratio of some unit.

Disagree. The people who get confused by decibels, are exposed to other people treating it like it's a unit in its own right. I agree that what the parent described, should be done. If it was what was done, this article wouldn't exist.

As I've said in the other comment, I believe this should be ultimately addressed by the SI.