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 is simply distinct, only connected by the fact that it represents some ratio in the logarithmic fashion. Treat any new dB unit you haven't seen as an alien.
> 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. :)
people are often confused by decibels because the necessary disambiguation is more often than not absent (see: spec sheets of some kind of appliance talking about noise)
That is of course not true. dB without reference is perfectly fine to use for gain and attenuation. dBm or any of the variants would be flat out wrong.
But we used to use the same unit for the absolute measure and the relative measure, like degrees Celcius/Fahrenheit. (Okay, % vs. %p is different but is probably an exception.) I see no particular reason to avoid suffixes in such situations.
When I worked on a radar project, my fellow radar engineers (I'm software) used dB a lot. A lot of them would actually agree with the article, but historical sometimes wins even when you're aware of its shortcomings. Aren't we the same in software anyway? The email protocol, terminal escape sequences, the UX of git command line, etc... Each of those could have an "X is ridiculous" blog post (and I would enjoy every single one).
One upside of dB not touched in the article is that it changes multiplication into addition. So you can do math of gains and attenuations in your head a bit more conveniently. Why this would be useful in the age of computers is confusing, but on some radio projects both gains and losses are actually enormous exponents when expressed linearly, so I sort of see why you would switch to logs (aka decibels). Kinda like how you switch to adding logs instead of multiplying a lot of small floats for numerical computing.
As a European if somebody tells me the diagonal size of a display in cm or meter, I'm simply not able to "grasp" it. I need to whip out the calculator and divide by 2.54, turning it into inches. It's just how monitors are measured in my head at this point.
Statistics once got me off-guard because that historical baggage. I thought I knew the probability theory pretty well to carry it to Statistics, but man, Statistics is a very different beast because it developed independently of Mathematics.
While I thoroughly enjoyed reading this piece of internet-rant, I've to argue that dB is still probably the best we have on this!
In RF engineering, expressing signal levels in dBm or gains in dB means you can add values instead of multiplying, which definitely appeared like a huge convenience for my college assignments! A filter with -3 dB loss and an amplifier with +20 dB gain? Just add. You can also use this short notation to represent a variety of things, such as power, gain, attenuation, SPL, etc.
I guess, engineers don’t use dB because they’re masochists (though many of them surely are). They use it because in the messy world of signals, it works. And because nobody knows anything that might work better!
There's nothing wrong with using a logarithmic system, that's not the complaint here. The complaint is that using decibels instead of bels is weird, and also that it's a scale and not a unit but people use it as if it was a unit without specifying a reference point, and also that the scale changes for different base units. Crazy how many people here are missing the point.
dBm is fully defined. Its reference is 1 mW into 50 ohms. I agree that using dB as a unit and not as a comparison (10 dB more power) is confusing, though.
A pet peeve I share! An expanded version of this article should become the article on decibels on Wikipedia.
I've read that article many times over my life and for the first couple times came back thinking I was too dim to understand.
Transparently leading it with "Here's something ridiculously overcomplicated that makes no sense whatsoever..." wouldn't fit Wikipedia's serious voice but actually be pedagogically very helpful.
Abbreviation confusability is relative to { in fact one might say measured by ;-) - number? entropy? etc. } the listener/reader's knowledge/exposure, much as sound levels need a reference distance.
I have heard "bare K" refer to a great many different things, not just kilobits (transmission) or kilobytes (storage) or kilograms (drug trade) or kilometers (foot races) and on & on, but pages or items or etc.
The fundamental problem is that some humans like to abbreviate while others get caught and annoyed by the necessary ambiguity of such abbreviation. Sometimes this can be the very same human in different contexts. ;-)
In fact, there even seems to be some effect where "in the know people" do this intentionally - like kids with their slang - as a token of in-group membership. And yes, this membership is at direct odds with broader communication, by definition/construction. To me this article seems to be just complaining about "how people are". So it goes!
This is the primary complaint. The secondary one about voltage and power and the ambiguity of the prefix itself was addressed in another comment (https://news.ycombinator.com/item?id=44059611).
> I have heard "bare K" refer to a great many different things
The worst of the worst is when it refers to kilometres. Like, "I'm selling my car on the used market and its odometer is 150k", where they mean "150k km", but stacked prefixes are not allowed in metric, so the correct notation is "150 Mm" or "150 megametres".
I get immense pushback whenever I point this out - the response is usually along the lines of "but you know what I meant", and it inherently assumes that km is the universal unit for talking about distance traveled by car.
I point out that this is as ridiculous as saying "the hard drive is 4k GB" because they grew up with gigabytes; no, the correct notation is either "4000 GB" or "4 TB".
Also regarding bare k or kilo (especially キロ in Japanese), you can say something ridiculously ambiguous like "My scooter goes up to 30k for 90k and weighs 20k" (respectively km/h, km, and kg).
In 3D printing, I often catch people talking acceleration in kilo-milli-meter/second². Written and pronounced "16k accel". Instead of writing "16m/s²" and pronouncing "16 accel".
I have nightmares of 150km meaning kilo-miles instead of kilo-metre. And when I say that my car has 260 mega-meter on the odometer, even people born metric look at me funny.
And don't get me started on MB vs MiB. I have seen so many stupid production outages because of people miss-allocating resources by confusing SI and IEC bytes.
Here's another related one that always bothers me: When you say something's loudness in decibels, you also need to specify a measurement distance.
The author of this article even accidentally makes this omission:
> It’s 94 dB, roughly the loudness of a gas-powered lawnmower
And that distance is very important; the actual sound pressure measured is proportional to distance^2. So for a lawnmower measuring 94dB, let's say we assume that we're measuring at 1m. At 2m away, the sound is actually 91dB.
And don't get me started about the fact that a halving in power is 3dB, that's just wacky. I wish we used base 2.
> And that distance is very important; the actual sound pressure measured is proportional to distance^2.
While we're sniping nerds, the inverse square law only applies in the far field (which is tautologically "far enough away for the source to behave as a point source and follow the inverse square law"). That's probably a good bit further than 1m for a lawnmower in the physical world. For loudpseakers you have to be about 2m away before the inverse square law kicks in, unless they've been designed to operate as line sources which decay linearly for a very long distance. For loud sound sources near barriers like the ground they behave like half point sources, which will eventually act like point sources but there's a good bit of distance before it is really measurable.
Do a deep dive into audio vu Meters and how they got calibrated. Without being 100% sure, it's basically a totally subjective model, where back in the 1920s the BBC and some US company decided to assert "like us" and two models persist which have been retconned into some BIPM acceptable ground truth but it basically was "test it against the one we made which works"
The hysteresis in the coil-magnet meter response turned out to be a feature, not a bug.
Readit News
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. :)
The people who get confused by decibels, are exposed to other people treating it like it's a unit in its own right.
I agree that what the parent described, should be done. If it was what was done, this article wouldn't exist.
One upside of dB not touched in the article is that it changes multiplication into addition. So you can do math of gains and attenuations in your head a bit more conveniently. Why this would be useful in the age of computers is confusing, but on some radio projects both gains and losses are actually enormous exponents when expressed linearly, so I sort of see why you would switch to logs (aka decibels). Kinda like how you switch to adding logs instead of multiplying a lot of small floats for numerical computing.
Indeed – as evidenced by some parts of the world still using non-metric units in daily life or even engineering :)
In RF engineering, expressing signal levels in dBm or gains in dB means you can add values instead of multiplying, which definitely appeared like a huge convenience for my college assignments! A filter with -3 dB loss and an amplifier with +20 dB gain? Just add. You can also use this short notation to represent a variety of things, such as power, gain, attenuation, SPL, etc.
I guess, engineers don’t use dB because they’re masochists (though many of them surely are). They use it because in the messy world of signals, it works. And because nobody knows anything that might work better!
I've read that article many times over my life and for the first couple times came back thinking I was too dim to understand.
Transparently leading it with "Here's something ridiculously overcomplicated that makes no sense whatsoever..." wouldn't fit Wikipedia's serious voice but actually be pedagogically very helpful.
Maybe this blog post could work as a source, although it would be better to find something more established.
I have heard "bare K" refer to a great many different things, not just kilobits (transmission) or kilobytes (storage) or kilograms (drug trade) or kilometers (foot races) and on & on, but pages or items or etc.
The fundamental problem is that some humans like to abbreviate while others get caught and annoyed by the necessary ambiguity of such abbreviation. Sometimes this can be the very same human in different contexts. ;-)
In fact, there even seems to be some effect where "in the know people" do this intentionally - like kids with their slang - as a token of in-group membership. And yes, this membership is at direct odds with broader communication, by definition/construction. To me this article seems to be just complaining about "how people are". So it goes!
This is the primary complaint. The secondary one about voltage and power and the ambiguity of the prefix itself was addressed in another comment (https://news.ycombinator.com/item?id=44059611).
The worst of the worst is when it refers to kilometres. Like, "I'm selling my car on the used market and its odometer is 150k", where they mean "150k km", but stacked prefixes are not allowed in metric, so the correct notation is "150 Mm" or "150 megametres".
I get immense pushback whenever I point this out - the response is usually along the lines of "but you know what I meant", and it inherently assumes that km is the universal unit for talking about distance traveled by car.
I point out that this is as ridiculous as saying "the hard drive is 4k GB" because they grew up with gigabytes; no, the correct notation is either "4000 GB" or "4 TB".
Also regarding bare k or kilo (especially キロ in Japanese), you can say something ridiculously ambiguous like "My scooter goes up to 30k for 90k and weighs 20k" (respectively km/h, km, and kg).
I have nightmares of 150km meaning kilo-miles instead of kilo-metre. And when I say that my car has 260 mega-meter on the odometer, even people born metric look at me funny.
And don't get me started on MB vs MiB. I have seen so many stupid production outages because of people miss-allocating resources by confusing SI and IEC bytes.
/rant
The author of this article even accidentally makes this omission:
> It’s 94 dB, roughly the loudness of a gas-powered lawnmower
And that distance is very important; the actual sound pressure measured is proportional to distance^2. So for a lawnmower measuring 94dB, let's say we assume that we're measuring at 1m. At 2m away, the sound is actually 91dB.
And don't get me started about the fact that a halving in power is 3dB, that's just wacky. I wish we used base 2.
While we're sniping nerds, the inverse square law only applies in the far field (which is tautologically "far enough away for the source to behave as a point source and follow the inverse square law"). That's probably a good bit further than 1m for a lawnmower in the physical world. For loudpseakers you have to be about 2m away before the inverse square law kicks in, unless they've been designed to operate as line sources which decay linearly for a very long distance. For loud sound sources near barriers like the ground they behave like half point sources, which will eventually act like point sources but there's a good bit of distance before it is really measurable.
The hysteresis in the coil-magnet meter response turned out to be a feature, not a bug.
This line killed me. I literally laughed out loud.