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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#71

Post by badlibrarian »

Horsepower is a unit of measurement. There's hp and bhp and hpE and...

"Other names for the metric horsepower are the Italian cavallo vapore (cv), Dutch paardenkracht (pk), the French cheval-vapeur (ch), the Spanish caballo de vapor and Portuguese cavalo-vapor (cv), the Russian лошадиная сила (л. с.), the Swedish hästkraft (hk), the Finnish hevosvoima (hv), the Estonian hobujõud (hj), the Norwegian and Danish hestekraft (hk), the Hungarian lóerő (LE), the Czech koňská síla and Slovak konská sila (k or ks), the Serbo-Croatian konjska snaga (KS), the Bulgarian конска сила, the Macedonian коњска сила (KC), the Polish koń mechaniczny (KM) (lit. 'mechanical horse'), Slovenian konjska moč (KM), the Ukrainian кінська сила (к. с.), the Romanian cal-putere (CP), and the German Pferdestärke (PS)." [1]

Decibel is not a unit of measurement. Decibels are a relative measurement. It tells you how much louder or powerful something is relative to something else. And frankly far less ridiculous than horsepower, which has a hilarious Wiki article if you read it with a critical mindset.

Deriving some of the constants without Googling is a fun exercise to verify that you're not as smart as you think you are. "Hydraulic horsepower = pressure (pounds per square inch) * flow rate (gallons per minute) / 1714"

[1] https://en.wikipedia.org/wiki/Horsepower

Re: The scientific “unit” we call the decibel

#72

Post by rocqua »

neepi wrote: post #37
eru wrote: post #32

Earlier quoted context omitted.

Obviously there are better ways. The author mentioned several. Eg you could clean up the naming of the variants of the unit, and make it no less useful for RF work, and strictly better in general.

Sorry but no. Absolutely no one cares about the mathematical purity of a unit like the decibel. It's a hammer that turns log stuff into easy to work with linear stuff. It's x10 because that turns into reasonably easy to use numbers with enough precision to use casually. Otherwise it's just a log ratio. Any suffix is a log ratio to a reference value for the entire system (dBv / dBm etc). Say in a 50 ohm system I have…

Have you considered the world outside of your expertise? Or the legibility of your field to people adjacent to it?

dBs work well for RF once people get used to a few quirks. The problem arises when it gets applied to other fields as units, or when people from adjacent fields want to cooperate with people from the RF field.

Re: The scientific “unit” we call the decibel

#74

Post by rocqua »

atoav wrote: post #61
eru wrote: post #32

Earlier quoted context omitted.

Obviously there are better ways. The author mentioned several. Eg you could clean up the naming of the variants of the unit, and make it no less useful for RF work, and strictly better in general.

There are better ways, if you optimize for ease of understanding and not ease of use. dB-based units make working between parts of a circuit, different devices etc. a breeze because adding 6dB in one part and removing it in another will result in no change in level. This is something the totally uninitated use every day in audio applications (typically that would be dBFS). What other system do you propose? One where…

dBFS is mostly fine. It's not used to communicate about loudness to anyone beyond experts. Loudness of machines is just specified as dB, and that gives manufacturers soooo much wiggle room, as to be useless.

Re: The scientific “unit” we call the decibel

#75

Post by mikewarot »

rocqua wrote: post #66
atoav wrote: post #21

But dB is not a unit, it is a multiplier. dB on its own is unitless and if we say "X is reduced by 6 dB" you know that the value of X is half of what it was before (×0.5) if something is amplified by 6 dB it is double of what it was before (×2.0)¹ Note that the unit only starts to play a role when you reference your dB value to some absolute maximum, e.g.: dBV which is referenced to 1V RMS dBu which is referenced to…

> But dB is not a unit, it is a multiplier. dB on its own is unitless. The point of the article is exactly that this should be the case. But it ends up not being the case. Mostly because people use dB with reference to some assumed baseline. But also because a 20db change could be a 10x change conpared to baseline, or a 100x change compared to baseline, depending on what unit you are measuring in.

20 dB is always the same, actually. If you multiply voltage (and thus current as well) by 10:1 (20 db) the power is multiplied by 100:1 (also 20 dB)

Re: The scientific “unit” we call the decibel

#76

Post by severusdd »

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!

Re: The scientific “unit” we call the decibel

#77

Post by neuroticnews25 »

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…

I think the "whining" is just a stylistic choice and an excuse to talk about the things he finds worth noting. I didn't perceive the tone of the article as negative.

Re: The scientific “unit” we call the decibel

#78

Post by em3rgent0rdr »

> 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 out loud. For instance, the dynamic range of 16-bit audio (which is generally all the range that our ears care about) is 96 dB, while volume increments smaller than 1 dB aren't really noticeable, so decibel makes it easy to communicate volume levels without saying "point" or writing a "." or breaking out exponential notation. Even in fields other than audio the common ranges also conveniently will be around 1 dB for being on the verge of significance to around 100 dB or 200 dB for the upper range. (Also the whole power vs root-power caveat is simply something users of dB have to be cognizant of because we need to stick with one or the other to make consistent comparisons, and at the end of the day physical things hapen with power.) So while decibels may seem ridiculous, they actually are quite convenient for dealing with logarithmically-varying numbers in convient range from 1 dB to around 100 dB or so in many engineering fields.

Re: The scientific “unit” we call the decibel

#79

Post by ajuc »

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…

You can use logarithmic scale without making it a pseudo-unit that changes the factors depending on the application.

Additionally - attacking people you don't know for ignorance because they have different opinions is very narrowminded.

Re: The scientific “unit” we call the decibel

#80

Post by atoav »

rocqua wrote: post #66
atoav wrote: post #21

But dB is not a unit, it is a multiplier. dB on its own is unitless and if we say "X is reduced by 6 dB" you know that the value of X is half of what it was before (×0.5) if something is amplified by 6 dB it is double of what it was before (×2.0)¹ Note that the unit only starts to play a role when you reference your dB value to some absolute maximum, e.g.: dBV which is referenced to 1V RMS dBu which is referenced to…

> But dB is not a unit, it is a multiplier. dB on its own is unitless. The point of the article is exactly that this should be the case. But it ends up not being the case. Mostly because people use dB with reference to some assumed baseline. But also because a 20db change could be a 10x change conpared to baseline, or a 100x change compared to baseline, depending on what unit you are measuring in.

Yes but my conclusion would not be that Decibels are ridiculous, but that "People don't understand Decibels".

Decibels are okay. They are useful. They work. The problem is that people use referenced decibel values without adding anything that would allow us to understand which reference was used.

Maybe one could have come up with a better numeric way of doing the same thing (I am missing a proposal for this in the blog post), but then you'd have the XKCD-yet-another-standard problem. Everything uses dB for ages now, so dB it is or you need to convert between one and another all the time.

As an audio engineer I have no issue with dB as a unit. It is much better than using raw amplitude numbers.

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