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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

#241

Post by regularjack »

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…

There is no such thing as full volume, and there is not such thing as zero volume.

Re: The scientific “unit” we call the decibel

#243

Post by viraptor »

klodolph wrote: post #234
sanderjd wrote: post #200

Earlier quoted context omitted.

> 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!

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 is like going to another planet and hearing "he's 3". Of course it's on a logarithmic scale, offset to -5 as starting point, counting the skin shedding events - clear in context and you should've known that.

Re: The scientific “unit” we call the decibel

#244

Post by twelvechairs »

hgomersall wrote: post #201
weinzierl wrote: post #193

Earlier quoted context omitted.

"decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity." Except they are not. 1 dB can sometimes mean a ratio of ~ 1.26 and other times it can mean a ratio of ~ 1.12. "In every context where decibels are used, either the unit they qualify is explicitly specified, or the unit is implicity known from the context." Maybe in university, but certainly not in the real w…

It's a power ratio. 1dB always means a power ratio of 1.26. That might mean a voltage or current ratio, say, of 1.12, but that is because the relationship between voltage ratios and power ratios is a simple square.

The other side of the authors discussion is the use of 'decibels' to describe 'loudness'. The big difficulty there is that 'loudness' is a sense perception that varies between people and in different contexts. The article touches on this 'weighted to mimic human hearing...' but doesnt mention the systems to do this - DB(A) and others, none of which achieve scientific perfection.

Our senses are all like this - for the same reason we have dozens of systems to describe color. And why perfume and wine makers can never agree descriptions.

Re: The scientific “unit” we call the decibel

#245

Post by UncleMeat »

xeonmc wrote: post #206
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…

Interviewer: "So what's the fastest you've gone on your bike?" Kid: "Thirty." Interviewer" "Thirty what?" Kid: "Umm..." Kid: "Speed." [0] https://www.youtube.com/watch?v=OYt1kqDNlMY

"I was doing 70 down the highway" is absolutely the sort of thing people say. From context (this conversation takes place in the US, most highways have a speed limit somewhere around 60-70mph) people understand that you are talking about miles per hour.

Re: The scientific “unit” we call the decibel

#246

Post by sgarland »

pwdisswordfishz wrote: post #157
TheOtherHobbes wrote: post #119

Earlier quoted context omitted.

This like arguing that aspect ratios are stupid and wrong because sometimes they apply to a screen which is really big and sometimes it's really small and sometimes they apply to a physical print or a photo or a billboard or a vintage TV and sometimes it's a jpg or a PNG. Aspect ratio is a ratio. It can be a ratio between pixel counts, or between print dimensions, or physical display dimensions. All of which are usef…

Why, you're right: aspect ratios are stupid because people often don't bother distinguishing between SAR, PAR and DAR, leading to lots of confusion. And sometimes even mistake the ratio of pixel densities for the pixel aspect ratio: https://trac.ffmpeg.org/ticket/11279 https://trac.ffmpeg.org/ticket/11284

Nothing better than spending hours encoding something, only to discover you got one of those wrong.

Re: The scientific “unit” we call the decibel

#247

Post by baxtr »

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…

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

Print this, frame this, put this up on walls in schools, offices, heck even outdoor on large billboards!

Re: The scientific “unit” we call the decibel

#248

Post by DonHopkins »

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…

Some people just hate certain numbers.

Many buildings don't have a 13th floor because superstitious people think it's unlucky.

Some people lose their shit at 8647 because paranoid delusional people think it's out to kill them.

Re: The scientific “unit” we call the decibel

#249

Post by hgomersall »

weinzierl wrote: post #240
hgomersall wrote: post #201

Earlier quoted context omitted.

It's a power ratio. 1dB always means a power ratio of 1.26. That might mean a voltage or current ratio, say, of 1.12, but that is because the relationship between voltage ratios and power ratios is a simple square.

I understand that and it just reinforces my point. What 1 dB essentially means is highly dependent on a most of the time silent context.

No, it always means a power ratio. That sometimes can imply something else, but that's on you to work that out.

Re: The scientific “unit” we call the decibel

#250

Post by jancsika »

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…

> The human-perceived loudness level is dB(A) and similar.

But db(A) doesn't really measure that for anything but sounds that could cause hearing damage, or test tones. You've essentially taken a newcomer's problem of underspecification and carried it into the given domain.

I feel like it'd be better to say dB(A) measures flaunkis, which is defined by the human frequency response. Then the newcomer's next question will be something like, "how do I use flaunkis to compute the loudness of a music recording?" And that's the right question to ask, because the answer is: it's complicated. :)

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