Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The scientific “unit” we call the decibel

lcamtuf.substack.com

Post reply on HN
Print view View original

301–310 of 511 posts

Re: The scientific “unit” we call the decibel

#301

Post by drob518 »

sanderjd wrote: post #200
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…

> In every context where decibels are used, either the unit they qualify is explicitly specified, or the unit is implicity known from the context. The author's whole point is that this is not true. To adapt your analogy, it's not like being mad at the number three, it's like being mad about people not attaching any units to the number three, arguing that it's clear in context. It isn't!

Just because the author is ignorant of the context doesn’t mean that the engineers working in those fields are. They use it because it all makes sense in context.

Re: The scientific “unit” we call the decibel

#302

Post by viraptor »

calmbonsai wrote: post #65

If you're specifying decibels in written form you always include the basis or you're simply being incomplete with your units. I don't understand the complaint there. In casual conversation, the context implies the basis. Dealing with decibels is also another shorthand to know the domain has a wide enough value gamut such that logarithmic values (where addition is multiplication) makes sense. See also, the Richter sca…

> I don't understand the complaint there.

The problem is that almost nobody does. I can't remember the last time outside of HN comments here that I've seen dB(A) or similar in real world.

Re: The scientific “unit” we call the decibel

#304

Post by karmakaze »

The writing style is antagonistic like a clickbait title. I find it bothersome. I would have much preferred an organized breakdown of all the different ways dB are used and what they mean instead of a random rant. It complains about how unscientific 'the' unit is, knowing that it's not a single unit then adds little to sort it out.

Re: The scientific “unit” we call the decibel

#305

Post by drob518 »

viraptor wrote: post #243
klodolph wrote: post #234

Earlier quoted context omitted.

Sure, but the author is wrong. “How old is your son?” “He’s 3.” Clear in context. People write things like dB SPL (A-weighted) in spec sheets because spec sheets benefit from being unambiguous. Most of the time it’s really clear, like you’re talking about insertion loss or amplifier gain and there’s only one reasonable way to interpret it.

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…

Then your complaint is with the dropping of units, not dB.

Re: The scientific “unit” we call the decibel

#306

Post by pzo »

icehawk wrote: post #299
pzo wrote: post #288

Earlier quoted context omitted.

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.

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

Re: The scientific “unit” we call the decibel

#307

Post by jampekka »

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…

> For instance, in the case of loudness of noise to human ears in air, the unit can be taken to be dBA (in all but rare cases which will be specified) measured with an appropriate A-weighted sensor, relative to the standard reference power level.

This was covered in the article. But also it was discussed why things aren't this simple.

> People who assume that everyone is an idiot but themselves are rarely correct.

Indeed.

Re: The scientific “unit” we call the decibel

#308

Post by sanderjd »

rusk wrote: post #217
sanderjd wrote: post #205

Earlier quoted context omitted.

I'm sorry, but did you read the article? This is not the complaint. If decibels were used only to measure sound relative to "experienced loudness" there would be no complaint. The complaint is that it is used in many other ways, often without distinguishing what the base unit is.

The issue is that it’s not “well defined” that it’s somehow subjective. But the whole point with a logarithmic scale is the small values don’t matter.

This isn't what the article is about!

Re: The scientific “unit” we call the decibel

#309

Post by 49pctber »

timerol wrote: post #296
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.

Yeah, that's a better way of thinking about it. That way you don't have any phantom bookkeeping like the way I was taught. The units are still right there.

Re: The scientific “unit” we call the decibel

#310

Post by davrosthedalek »

skrebbel wrote: post #207
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…

To be frank, your comment just reads to me as a "stockholm syndrome" type reaction to a needlessly complex unit that you're intimately familiar with. You see the same in HN threads where people complain that eg Git or Rust are needlessly complex, there's a swath of people who are so emotionally invested in how well they understand the ins and outs of Git resp Rust that any suggestion that maybe things could be better…

Ok, I bite. Please come up with a mapping of 0 to 100 to -inf dB to 0 dB attenuation.

And then put two in series. Is there a simple formula to calculate the total attenuation?

This works flawlessly with dB. Just add. And it doesn't matter how you break it: -20dB and -20 dB in series is the same as -40dB and 0dB.

Post reply on HN