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The scientific “unit” we call the decibel

lcamtuf.substack.com

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Re: The scientific “unit” we call the decibel

#291

Post by lxgr »

fouronnes3 wrote: post #36

When I worked on a radar project, my fellow radar engineers (I'm software) used dB a lot. A lot of them would actually agree with the article, but historical sometimes wins even when you're aware of its shortcomings. Aren't we the same in software anyway? The email protocol, terminal escape sequences, the UX of git command line, etc... Each of those could have an "X is ridiculous" blog post (and I would enjoy every s…

> A lot of them would actually agree with the article, but historical sometimes wins

Indeed – as evidenced by some parts of the world still using non-metric units in daily life or even engineering :)

Re: The scientific “unit” we call the decibel

#292

Post by lxgr »

hgomersall wrote: post #273
lxgr wrote: post #257

Earlier quoted context omitted.

Yes, but that, i.e. putting the burden of disambiguating some meaning from context on the receiver instead of the sender, is just bad communication.

What? Blaming a bad communicator for bad communication is fine. Blaming their words because they used them badly is not.

What about blaming a common but confusing usage of some words pervasive in some fields?

Re: The scientific “unit” we call the decibel

#293

Post by etskinner »

Here's another related one that always bothers me: When you say something's loudness in decibels, you also need to specify a measurement distance.

The author of this article even accidentally makes this omission:

> It’s 94 dB, roughly the loudness of a gas-powered lawnmower

And that distance is very important; the actual sound pressure measured is proportional to distance^2. So for a lawnmower measuring 94dB, let's say we assume that we're measuring at 1m. At 2m away, the sound is actually 91dB.

And don't get me started about the fact that a halving in power is 3dB, that's just wacky. I wish we used base 2.

Re: The scientific “unit” we call the decibel

#294

Post by viraptor »

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.

Glad we never changed them and still drink in hogshead, use the original foot reference, and never resolved what base is a megabyte. ;)

Re: The scientific “unit” we call the decibel

#295

Post by hgomersall »

lxgr wrote: post #281
hgomersall wrote: post #274

Earlier quoted context omitted.

In which case they're misusing it, which is hardly a problem with the notation.

As I read it, the criticism of TFA is directed at how people actually use the notation, not how it ought to be used in an ideal universe.

But people misuse words and notation all the time without anyone arguing they're ridiculous. I use dBs on a daily basis with plenty of other people and never have any trouble. Indeed, we'd struggle if we had to use something else.

Re: The scientific “unit” we call the decibel

#296

Post by timerol »

49pctber wrote: post #284

The idea that helped make decibels click for me is that they're a way to quickly do both dimensional analysis and gain/attenuation calculations at the same time. "Plain" decibels are simply (power) ratios. These can describe multiplicative changes in power. These are positive for gains (like in a power amplifier) or negative for attenuations (like path loss). They are unitless quantities. Decibels add. A ten 10 dB ga…

> 2 mW / 1 mW = 2 = 10^(3/10) = 3 dBm

It's worth noting that this is wrong, in exactly the way that makes decibels confusing. 3 dBm is an absolute power figure (about 2 mW). 2 mW / 1 mW is a ratio of 2 (about 3 dB).

2 mW / 1 mW = 2 = 10^(3/10) = 3 dB.

2 mW = 2 * 1 mW = 10^(3/10) * 1 mW = 3 dB (1 mW) = 3 dBm.

Re: The scientific “unit” we call the decibel

#298

Post by seba_dos1 »

viraptor wrote: post #258
nyeah wrote: post #239

Earlier quoted context omitted.

It makes perfect sense that the sliders start at 0dB and go down to -inf. Maybe you don't understand it, but it definitely makes sense. Everyone who uses dB has also tried a % scale with 100% as 0dB, and then later made a conscious choice to figure out how dB work. Maybe they're all in a conspiracy to make things needlessly complex. But that's not the only possibility.

> and then later made a conscious choice to figure out how dB work. You're just projecting your ideas here. I've not made that choice, it's just the only option in a lot of software - I'd like my % slider back.

% slider sounds like a good idea until you actually have to use it.

Re: The scientific “unit” we call the decibel

#299

Post by icehawk »

pzo wrote: post #288
klodolph wrote: post #262

Earlier quoted context omitted.

It’s understood in context, that’s the point.

no it's not - it's assumed by maybe taking the most likely unit (year). But if the conversation is in hospital with your kid having emergency I guess doctor would appreciate to know if they will have to do surgery on 3 months child or 3 years kid.

A 3 month old kid looks very different to a 3 year old kid.

Re: The scientific “unit” we call the decibel

#300

Post by _kb »

lxgr wrote: post #287
_kb wrote: post #279

Earlier quoted context omitted.

> volume sliders start at 0 dB and then go down to negative $MUCHO, until complete silence at -Infinity. And then this same unit is also used to measure how loud my coffee machine is. They're not the same unit, at all. The audio software is a skeuomorphism from an analogue mixing console that is applying a change to a signal. 0 is unity gain and deviation from this describes an amplitude variation. This is important,…

> They're not the same unit, at all. Exactly, so why label two different things using the exact same letters in a potentially ambiguous context.

Because it’s not ambiguous.

If I pay for something in Australia and the bill comes to $50 this has meaning within that context.

I receive a bill in Zimbabwe for $50 this also has meaning within that context.

These values are not equivalent.

Ditto if I were to say it’s 30 degrees out. You may interpret that as either a good day for the beach, nice weather for ice skating, or we need to bear north-northeast depending on what context we share.

Language is messy.

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