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

Re: The scientific “unit” we call the decibel

#261

Post by DonHopkins » Thu, May 22, 2025, 1:37 PM UTC

Almost as annoying as Euler angles, which force you to choose an arbitrary ordering (XYZ, ZYX, ZXZ, …), while each choice is equally valid yet mutually incompatible, so there is no canonical “true” yaw-pitch-roll.

Not to mention gimbal-lock singularities, wrapping discontinuously at +/-PI, mapping one orientation to many triples, and forcing you to juggle trig identities just to compose two spins.

To pure mathematicians obsessed with elegant unambiguous coordinate-free clarity, Euler’s pick-any-order gimmick is like hammering tacky street signs onto the cosmos: a slapdash, brittle hack that smothers the true geometry while quaternions and rotation matrices sail by in elegant, unambiguous splendor.

Re: The scientific “unit” we call the decibel

#262

Post by klodolph » Thu, May 22, 2025, 1:37 PM UTC

RichardLake wrote: post #255

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 depends, the dropped unit could be either a year or a month.

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

Re: The scientific “unit” we call the decibel

#263

Post by viraptor » Thu, May 22, 2025, 1:38 PM UTC

UncleMeat wrote: post #245

xeonmc wrote: post #206

Earlier quoted context omitted.

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.

And yet, on the internet without the extra context, I can't tell if you're going slowly in km/h or the usual in mph. With dB that depends on whether you're taking to a person familiar with the context-specific conventions or not.

Re: The scientific “unit” we call the decibel

#264

Post by Aachen » Thu, May 22, 2025, 1:38 PM UTC

sgarland wrote: post #238

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…

> The units are implied by the context. This is the absurd part. There do exist other ratios that masquerade as units, e.g. specific gravity, and its meaning also changes depending on what you’re using it for - liquids are compared to pure water at 4 C, gases are compared to air at 20 C. As the parent comment points out, you can get used to things with experience. That doesn’t make them any less absurd. Look at Fahre…

Coulomb? In a discussion about units, leaving out the degree word or symbol made me initially try to parse it as that you must mean it literally, though context quickly makes clear that isn't the case ^^'

Re: The scientific “unit” we call the decibel

#265

Post by klodolph » Thu, May 22, 2025, 1:39 PM UTC

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…

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.

Re: The scientific “unit” we call the decibel

#266

Post by viraptor » Thu, May 22, 2025, 1:39 PM UTC

dotancohen wrote: post #212

xeonmc wrote: post #206

Earlier quoted context omitted.

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

KSP measures funds in some unitless value, it drives me nuts. Everything else is almost (but not quite) perfect.

Just pretend it's a Jane Austen novel and you're earning 500. Pounds? Pieces of gold? Sheep? Who knows really ;)

Re: The scientific “unit” we call the decibel

#267

Post by remram » Thu, May 22, 2025, 1:43 PM UTC

cesaref wrote: post #127

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 i…

I didn't get that reading the article. The author acknowledge that ratios are useful, but that there are specific problems in how we use this unit and how we picked and express the reference scales.

> On the face of it, the idea makes sense.

Your specific example is a pure ratio so there's no problem with it (there is no reference). Apart from the fact that I have to guess whether you are measuring volts or watts through your cables, of course...

Re: The scientific “unit” we call the decibel

#268

Post by viraptor » Thu, May 22, 2025, 1:43 PM UTC

kristjank wrote: post #33

This seems exceedingly ignorant of the work decibels do in telecommunications, RF and fibre engineering. The voltage vs power relationship is something that exists and is a core memory of beginner blunders in the field, but it boils down to a simple 10 vs 20 division operation. Besides that, the decibel simplifies a lot of multiplying very small and very big numbers to summing of two-digit numbers that you can do in…

> and is a core memory of beginner blunders in the field

Are you into creating artificial issues to make understanding things harder? If not... what's your point?

> doubt that the OP has any practical experience

One quick search would save you from writing a very silly thing.

Re: The scientific “unit” we call the decibel

#269

Post by [deleted] » Thu, May 22, 2025, 1:44 PM UTC

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…

[deleted]

Re: The scientific “unit” we call the decibel

#270

Post by Aachen » Thu, May 22, 2025, 1:45 PM UTC

cesaref wrote: post #127

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 i…

> 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'.

I'm not a sound engineer, so to check my understanding: would this not be the case for any other scale indicator?

If you have a cable that loses 4m and you're sending 6m into it, you'd not get 2m out?

(The m being milli here, as in millivolts or whatever unit would be useful here — leaving it unspecified to keep the comparison to dB as close as possible)