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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

#371

Post by anthomtb »

baxtr wrote: post #247
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!

And before doing any of that, get it tattooed onto your own forearm.

Re: The scientific “unit” we call the decibel

#372

Post by seanhunter »

jayd16 wrote: post #351
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.

When you say 35 it would be strange for it to be anything but years. 3 days, weeks, months or years are ironically all common units when someone is "3".

No one actually says "my child is 3" meaning anything other than 3 years. They would say "3 days", "3 weeks" or "3 months" meaning the other lengths of time.

Re: The scientific “unit” we call the decibel

#373

Post by waffletower »

This is an armchair rant with a very narrow complaint. The decibel unit has objective utility in both analog and digital signal processing and the field of audio engineering. It is far from meaningless in filter design and a useful reference for software and hardware interfaces that employ them.

Re: The scientific “unit” we call the decibel

#374

Post by bsteinbach »

The power vs voltage thing I think comes from the historical connection of dB to sensing waves. Because you can change impedance to match any sensor, but power is conserved, power was just more often more important to discuss than voltage. I still have to look it up every time whether 10x is 10 or 20 dB.

Re: The scientific “unit” we call the decibel

#375

Post by klodolph »

viraptor wrote: post #334
klodolph wrote: post #265

Earlier quoted context omitted.

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.

Audio, the only gotcha I’ve seen is that -10 is -10 dBu and +4 is +4 dBV. That one is sloppy.

But this comment doesn’t illustrate your point, and I still don’t really understand where you’re seeing this.

Re: The scientific “unit” we call the decibel

#376

Post by marcosdumay »

thowawatp302 wrote: post #335
pzo wrote: post #306

Earlier quoted context omitted.

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.

As long as you construct a strawmen strict enough that can be no ambiguity, and refuses to acknowledge any context where it's not enough, yeah, it always make sense in context.

Re: The scientific “unit” we call the decibel

#377

Post by klodolph »

sanderjd wrote: post #315
klodolph wrote: post #265

Earlier quoted context omitted.

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.

The explanation and motivating examples are in the article.

The article only had bad examples in it, I was hoping for perspective from someone that made sense.

The voltage / power example doesn’t make sense. It’s always power or voltage squared, which are equivalent when the load is resistive.

Re: The scientific “unit” we call the decibel

#378

Post by jameshart »

regularjack wrote: post #241
skrebbel wrote: post #207

Earlier quoted context omitted.

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.

‘There is no such thing as zero volume’ - can you expand on that?

Surely constant unchanging air pressure has zero volume?

Volume is the range of variation in air pressure, right? That can surely go down to zero.

It can also only meaningfully go up to about double the absolute mean air pressure, before what you are talking about becomes shockwaves of overpressure.

Re: The scientific “unit” we call the decibel

#379

Post by perching_aix »

teknopaul wrote: post #369

"This is nuts: it’s akin to saying that the milli- prefix should have different meanings depending on whether we’re talking about meters or liters." Were were here recently with "mega": Sometimes mega is squared as in megapixels. Sometime not as in megabytes. No biggie. Db in audio is a relative scale and that makes perfect sense. If you mixer goes + or - 6db that makes sense but can't be measured as power, your mixe…

> Sometimes mega is squared as in megapixels.

Is that right? A pixel is a 2D object already. It's not like e.g. with centimeters, where it's a 1D unit, so it becomes centimeters squared to form a 2D unit.

Re: The scientific “unit” we call the decibel

#380

Post by StableAlkyne »

teknopaul wrote: post #369

"This is nuts: it’s akin to saying that the milli- prefix should have different meanings depending on whether we’re talking about meters or liters." Were were here recently with "mega": Sometimes mega is squared as in megapixels. Sometime not as in megabytes. No biggie. Db in audio is a relative scale and that makes perfect sense. If you mixer goes + or - 6db that makes sense but can't be measured as power, your mixe…

> Sometimes mega is squared as in megapixels. Sometime not as in megabytes.

Even worse is Mega in Megabytes could be 1,000,000 or 1,048,576 and it's more or less up to you to know what's what

(Yeah, there are formally megabytes/mebiibytes/MiB/MB, but I honestly cannot recall the last time I heard anyone use anything other than just "megabyte" for 2^20 bytes... Or even wanted to refer to exactly 1,000,000 bytes. Other than decades ago when disk manufacturers wanted to make their hardware seem higher capacity than it really was)

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