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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#111

Post by em3rgent0rdr »

jeroenhd wrote: post #70
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…

The same can be said of any unit. "If you just learn to work with it regardless of its weirdness, it's completely normal" doesn't mean the standard isn't ridiculous. I don't think anyone has stated that a logarithmic scale is bad. The type of logarithmic scale changing depending on the field it's being used in, and the non-standard notation (dBm being used instead of dBmW for instance), is just inconsistent for no re…

> I don't see a practical reason why dB's normal use can't have been covered by normal prefixes

Because instead of numbers going like 1, 10, 100, 1k, 10k, 100k, 1M, 10M, 100M, 1G, and so on when using prefixes, we get a much more smoother numbers of 0 dB, 10 dB, 20 dB, 30 dB, 40 dB, 50 dB, 60 dB, 70 dB, 80 dB, 90 dB. You can see the the number for the dB get bigger, while when using prefixes the numbers get bigger two times in a row and then go back to smaller. With dB you usually just see a number from 0 to around +/- 100 or so. You can plot dB nicely as an axis of a chart and then see the slope of a curve in so many dB per decade.

Re: The scientific “unit” we call the decibel

#112

Post by yxhuvud »

neepi wrote: post #60
fouronnes3 wrote: post #53

Earlier quoted context omitted.

However you must concede that the perspective of an outsider can be refreshingly eye opening sometimes, even to experts. Especially when it reveals the arcane practices that make a field difficult to learn - for example here the point about the base being too implicit is very valid. The article is perhaps ignorant of a few things, but its criticism shouldn't be dismissed outright IMO. Accepting constructive criticism…

That would assume that the entire world hasn't already tried this a thousand times over. Measurements are standardised communication tools. If you start changing the definitions, things fall out of the sky and on your head.

No, changing definitions was exactly how we ended up with SI units. That was a very good (and necessary) thing and definitely not the sky falling down.

Re: The scientific “unit” we call the decibel

#113

Post by dj3l4l »

kazinator wrote: post #49

> This means that if you’re talking about watts, +1 bel is an increase of 10×; but if you’re talking about volts, it’s an increase of √10×. 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. Well no, because even if you are focusing on a signal measured in volts, the bel continues to be related to power and not voltage. As…

The Bel is a unitless quantity. Yes, by convention, in certain fields, it applies to the logarithm of the ratio of powers. But in other fields (for example, quantifying a change in the degree of evidence for a hypothesis, as in Bayesian probability theory) it is applied to a ratio of different quantities (in the Bayesian case, a ratio of probabilities). There is no reason why dB can't be used for any unit, and its meaning is incomplete until the denominator of the ratio within the logarithm is known.

This is the gripe that is being conveyed in this article. Mathematically, the Bel is unitless. It is only by additional context that one can understand the value of the denominator in the logarithm.

Re: The scientific “unit” we call the decibel

#114

Post by qmmmur »

neepi wrote: post #45
coolcase wrote: post #39

Earlier quoted context omitted.

They are units too. When you have regulations relating to sound they will say how many dB the limit is.

No. dB is not a unit. If it's quoted as a unit, then the person using it doesn't know what they are doing. dBx where x is some reference value is a unit and that means dB relative to the reference unit. So dBm/dBv etc are units. dB is not. Mathematically, dB is the ratio between two unit values and for example if you divide metres by metres you cancel the units.

Exactly. If someone says that "this plane is about 130dB" what they mean is in reference to 0dB given 0dB is the threshold of human hearing. It seems most people are confused by dB because they don't understand it provides a logarithmically scaled unit compared to a reference which happens to be quite useful for something like audio where our perceptual models are stacked with these types of curves.

Re: The scientific “unit” we call the decibel

#115

Post by kqr »

Ekaros wrote: post #110
dns_snek wrote: post #106

Earlier quoted context omitted.

You haven't addressed any points the author has made, we don't need to have "experience" in a field to know that ambiguous units are ridiculous and bad. When I'm buying a piece of string for my garden, I don't need to find an agricultural textbook to know whether "10 meters" in agriculture is the same as "10 meters" in engineering, and whether the definition of "meters" depends on whether the string is made out of co…

Well 10 millimetres of rain is different that 10 millimetres thickness for say branch...

At first I was going to contradict you but then I realised 10 mm of rain is actually a measure of volume or mass, corresponding to 10 kg, right?

And of course, people use it mainly as a rate, i.e. 10 kg per hour, or per four hours, or six hours, or 24 hours.

And it gets worse when we start talking about snow, the density of which can vary a lot!

Re: The scientific “unit” we call the decibel

#116

Post by em3rgent0rdr »

em3rgent0rdr wrote: post #78

> For some reason, the bel — again, what started as a sensible 10× increment — was soon deemed too big to use. I don’t quite know why: in other aspects of life, decimal notation suits us just fine. Decimal notation can be a tad cumbersome to write and speak. Meanwhile, decibel usage commonly results in nice simple numbers that range between 0 and 100, with the fractional digits often being too insignificant to say ou…

Its like why we use percent from 0% to 100% instead of speaking of ratios from 0 point something to 1.

Re: The scientific “unit” we call the decibel

#117

Post by iLoveOncall »

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…

Doesn't OP addres that multiple times in the article? He constantly reminds that the unit means vastly different things based on the domain, and focuses on acoustics after that, which is what every laymen would think about given the mention of decibels.

Re: The scientific “unit” we call the decibel

#119

Post by TheOtherHobbes »

svara wrote: post #62
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…

> makes me really doubt that the OP has any practical experience about the things they're talking about. Maybe not, but you can get used to many odd things given enough experience. I totally share the authors view. I don't usually have trouble grasping the definition of a unit, but dBs are just hilariously overloaded. The same symbol can literally mean one of two dimensionless numbers, or one of who knows how many ph…

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 useful in their own way, none of which are directly comparable, all of which are understandable in context.

dB is the same. It's a ratio split into convenient steps - more convenient than Bels would be - that compares two quantities. The quantities can be measured in different units. The units are implied by the context.

The only mild confusion is the relationship between voltage and power ratios. But that's a minor wrinkle, not a showstopping intellectual challenge.

Re: The scientific “unit” we call the decibel

#120

Post by metalman »

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…

sound IS funny, db does work, and for people building the things that produce or record sound. Useing db is just another unit used in engineering. Now if someone wants to get into the (very facinating), psychoacoustic side of sound, where another unit has been tried, "phons", prounounced fonz ;) , then it becomes clear that determining sound pressure levels is a tricky thing, as at the low end of perceptable sound the real world power of the actual sound is miniscule when converted into heat or mechanical power, and at the othete end a amp/speaker set up that was 100% efficient would only need 5 or 10 watts of electricity to power a stadium concert. we work with what we have, in a past lifeI got a degree in sound engineering, but barely practiced it, found myself way more into enjoying the products that have been built to be used, but am always greatfull to the people who make it possible, who on occasion are entertained by the sometimes exotic ways that I abuse the equipment, as the good ones take pride in having thought of and planed for such things, but do like confermation from the field. STC ratings anyone?
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