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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#331

Post by jwagenet »

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.

How about using kg for both mass and weight? At least as an American we learn lb is actually lb_f and lb_m or slug is used for mass. The weirdness is consistent with the rest of the system. In metric Newton exists as a separate and sane measure of force…

Re: The scientific “unit” we call the decibel

#332

Post by davrosthedalek »

lifthrasiir wrote: post #159
margalabargala wrote: post #141

Earlier quoted context omitted.

I would agree. Right now what we've got is basically "millis", and you just have to know whether the speaker is talking about length or mass. I like your proposal.

I actually want those suffixes mandatory, because there may be multiple plausible suffixes for each use. For example the loudness might be dB(A), dB(B), dB(C), dB(D) depending on the exact curve or even dB(SPL) if the sound pressure level is used as a proxy. So it is much more confusable than, say, "millis" when suffixes are implied.

There is a legitimate use of dB without a reference point. An attenuator attenuates by -20dB, not by -20dBm.

Re: The scientific “unit” we call the decibel

#333

Post by strbean »

drob518 wrote: post #324
sanderjd wrote: post #311

Earlier quoted context omitted.

This is literally the same as saying that you don't need to explicitly specify units in any field because "it all makes sense in context" to "engineers working in those fields". No. We've painstakingly figured out the right answer to this through the generations of doing science and engineering: You always specify units.

But obviously we don’t. So, there’s your counter proof.

Except the various disasters caused by assuming the wrong units (Mars Climate Orbiter, for example).

Re: The scientific “unit” we call the decibel

#334

Post by viraptor »

klodolph wrote: post #265
viraptor wrote: post #243

Earlier quoted context omitted.

That only works if you're already familiar with the context and system and assume other people are too and don't care about anyone new to that area. (Good luck coming to the audio equipment datasheet with no experience and figuring out what the dB means in each case) "He's 3" works because of the previous question and because everyone had experience of talking about age. dB for anyone not already knowing the answer i…

Maybe I just live on the planet, but I don’t have this problem with dB and to me, it sounds like you’re the alien. Maybe you could elaborate, or give a motivating example? I just don’t remember encountering the problem you’re describing, and it’s unfamiliar to me. There’s something about your experience that I don’t understand, but I don’t know what it is.

Moving from EE to audio to radio is enough to go through a few iterations of "people just write dB but mean completely different things". I got used to it, but that doesn't stop me from saying it's a bad idea and we should improve things for the next person.

Re: The scientific “unit” we call the decibel

#335

Post by thowawatp302 »

pzo wrote: post #306
icehawk wrote: post #299

Earlier quoted context omitted.

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

and thats the exact point - you assume doctor see the kid instead of you calling doctor or doctor is getting briefed by emergency stuff.

Exactly! It makes sense in context.

Re: The scientific “unit” we call the decibel

#336

Post by viraptor »

drob518 wrote: post #325
viraptor wrote: post #322

Earlier quoted context omitted.

Yes, that's what the whole article is about...

But it’s not. He’s raging against dB.

Yes. He's complaining against dB with no reference, not against dB(A) for example. (Apart from the naming of some of them being silly)

Re: The scientific “unit” we call the decibel

#337

Post by paipa »

dj3l4l wrote: post #230
paipa wrote: post #216

Earlier quoted context omitted.

The denominator isn't the issue. The context-dependent base of the logarithm is, which makes 1 Bel = 10x for some things and 1 Bel = 3.16x for others. I've never heard of decibels used in probability theory. Did they adopt it with the same baked-in bastardizations? Please tell me +10dB(stdev) = +10dB(variance) isn't a thing.

The problem stated in the article is that the unitless quantity of 1 Bel is effectively applied only to power ratios. It is of course true that one can transfer a scaling of powers into the base of the logarithm when we are trying to figure out what effective scaling of voltages corresponds to 1 Bel of power scaling, but it is ultimately more meaningful to state that a Bel is "only a scaling of power", which is a sta…

The puzzling thing is why they chose to adopt a term used to describe "only a scaling of power" to talk about log10 values. If 1 Bel simply meant 10x, I'd get it, but Bel has baggage and also means sqrt(10)x.

Is odds a power-like or amplitude-like quantity? If you can't tell, dB isn't the most fortunate choice. It's not like mathematicians need fake units to talk about unitless ratios and their logarithms.

Re: The scientific “unit” we call the decibel

#338

Post by observationist »

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.

If the doctor has trouble figuring out the difference between 3 months and years, there are bigger problems than specificity.

There are places specificity is necessary, and there are places the implicit assumptions people make are specific, and only need additional specification if the implication is violated. That's how language works - shortcuts everywhere, even with really important things, because people figure it out. There are also lots of examples of this biting people in the ass - it doesn't always work, even if most of the time, it does.

Re: The scientific “unit” we call the decibel

#339

Post by timerol »

lambdaone wrote: post #187

It's a bit like hating numbers, and saying "What do you mean by 'three'; what is it - three volts, three amps, three metres? Clearly 'three' is meaningless, and we should stop using it and all the other numbers besides." decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity. In every context where decibels are used, either the unit they qualify is explicitly speci…

> multiplier for some known value of some known quantity

Of course, unless it's a multiplier for an unknown value of a known quantity, like every amplifier, filter, and sensor specified in dB.

> For instance, in the case of loudness of noise to human ears in air, the unit can be taken to be dBA

Unless you're using dBB or dBC, but of course we all know exactly why you'd use dBC (more suitable for figuring out safety of high impulse, short events) or dBB (it's somewhere in between - you'll know it when you see it).

> The apparent excessive complexity is necessary, not invented to create confusion.

Wait, so writing dB instead of dBA is now necessary, not just convenient?

Re: The scientific “unit” we call the decibel

#340

Post by viraptor »

drob518 wrote: post #323
sanderjd wrote: post #316

Earlier quoted context omitted.

Yes. The point is that for some reason dB seems particularly susceptible to people dropping the units. For instance, I've heard loudness of sounds described in decibels for my whole life, and first saw the actual units people are describing when I read this article and thread today.

That’s because you’re a casual observer. If you’re an audio engineer, recording things, designing microphones, amps, or speakers, then you’d know it. Trust me. I’m a digital electrical engineer (computer engineering, basically). I thought that dBs were weird, too. My dad worked in microwave communications systems for his career and dBs are perfectly natural for him. Ditto my daughter who is an audio engineer. Droppin…

There are two paths: "it was weird but then I got used to it, you're just ignorant" or "it was weird, I got used to it, but we should improve the situation". I know which side I want to be on. Even if it takes decades like the data SI prefixes.
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