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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

#311

Post by sanderjd »

drob518 wrote: post #301
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!

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.

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.

Re: The scientific “unit” we call the decibel

#312

Post by viraptor »

nyeah wrote: post #260
viraptor wrote: post #258

Earlier quoted context omitted.

> and then later made a conscious choice to figure out how dB work. You're just projecting your ideas here. I've not made that choice, it's just the only option in a lot of software - I'd like my % slider back.

Right. Decibels are my idea.

Projecting in that context means you claimed what other people think/do, because it's what you think/do. It's about describing the conscious choices of others (where my experience disagrees for example) not about decibels specifically.

Re: The scientific “unit” we call the decibel

#313

Post by sanderjd »

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.

If you were writing a research paper or engineering artifact rather than having a casual conversation, you should specify the units ("years old") for age as well.

Re: The scientific “unit” we call the decibel

#314

Post by timerol »

The one thing that really resonates with me from this article is also the silliest thing: Why decibels instead of bels? Everyone has multiplied in scientific notation before, and making a power ratio of 10^4 = 4 B would be so much more intuitive for conversion to absolute figures. It's a completely silly complaint, given that it's literally just a decimal point instead of a d, but it would make mental math of absolute conversions that much faster, especially for people who don't live and breathe amplifier chains all day.

I want to live in a world where a radio can be specified as a -10.2 Bm sensitivity. -9 is three SI prefixes down from 1 mW, so less than 0.1 pW.

Re: The scientific “unit” we call the decibel

#315

Post by sanderjd »

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.

The explanation and motivating examples are in the article.

Re: The scientific “unit” we call the decibel

#316

Post by sanderjd »

drob518 wrote: post #305
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…

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

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.

Re: The scientific “unit” we call the decibel

#317

Post by radiowave »

throwaway290 wrote: post #52
formerly_proven wrote: post #47

Earlier quoted context omitted.

That's hilarious, though they do seem to get it right on the other, more in-depth pages.

Yep, the NIOSH meter app they recommend uses dB(A).

Though that's still incomplete, because (more of the context stuff that you just have to know already) the "A" here refers to the frequency-weighting scheme used in the measurement, and not to the reference level (which is SPL).

It should probably be given as: dB(A) SPL, or dB SPL (A-weighted).

Re: The scientific “unit” we call the decibel

#318

Post by drob518 »

CamperBob2 wrote: post #225
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…

dB is always relative, even when it appears to be an absolute unit. The 0 dB marking at the top of the volume slider on pro audio gear (more likely +3 or +6 or something similar to leave some headroom) means "0 dB relative to the maximum rated power level." In pro gear this will be an absolute industry standard of some sort, likely one where the load impedance is also defined. 1 milliwatt into 600 ohms or something l…

Exactly. dB is just a way to apply a logarithmic scale on a quantity that would have orders of magnitude range if working with a linear scale. It allows an engineer to quickly add up all the amplification and attenuation through a series of amps and filters without having to do a lot of uglier math. It’s not really a physical unit. It’s a marker that says that we’re working in the domain of logarithmic quantities of some other units.

Re: The scientific “unit” we call the decibel

#319

Post by BenjiWiebe »

Aachen wrote: post #270
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…

It's a ratio, not a fixed amount. The amount you lose depends on the amount you send.

Re: The scientific “unit” we call the decibel

#320

Post by BenjiWiebe »

remram wrote: post #267
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 thr…

So what I learned today, via another comment and confirmed with a dictionary, is that decibels (unspecified reference) is NOT pure ratio - it's a _power_ ratio. So it will be Watts, not Volts.
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