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Comment by weinzierl | Hacker News Reader

"decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity."

Except they are not. 1 dB can sometimes mean a ratio of ~ 1.26 and other times it can mean a ratio of ~ 1.12.

"In every context where decibels are used, either the unit they qualify is explicitly specified, or the unit is implicity known from the context."

Maybe in university, but certainly not in the real world.

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It's a power ratio. 1dB always means a power ratio of 1.26. That might mean a voltage or current ratio, say, of 1.12, but that is because the relationship between voltage ratios and power ratios is a simple square.

Exactly. I’ve never seen it otherwise.

I understand that and it just reinforces my point. What 1 dB essentially means is highly dependent on a most of the time silent context.

No, it always means a power ratio. That sometimes can imply something else, but that's on you to work that out.

Yes, but that, i.e. putting the burden of disambiguating some meaning from context on the receiver instead of the sender, is just bad communication.

What? Blaming a bad communicator for bad communication is fine. Blaming their words because they used them badly is not.

What about blaming a common but confusing usage of some words pervasive in some fields?

The other side of the authors discussion is the use of 'decibels' to describe 'loudness'. The big difficulty there is that 'loudness' is a sense perception that varies between people and in different contexts. The article touches on this 'weighted to mimic human hearing...' but doesnt mention the systems to do this - DB(A) and others, none of which achieve scientific perfection.

Our senses are all like this - for the same reason we have dozens of systems to describe color. And why perfume and wine makers can never agree descriptions.

That’s maybe what it “is”, but not the only thing people use it for in many fields. Very often, it’s a ratio between a measured quantity and some (implied) base unit of the same quantity.

In which case they're misusing it, which is hardly a problem with the notation.

As I read it, the criticism of TFA is directed at how people actually use the notation, not how it ought to be used in an ideal universe.

But people misuse words and notation all the time without anyone arguing they're ridiculous. I use dBs on a daily basis with plenty of other people and never have any trouble. Indeed, we'd struggle if we had to use something else.

> But people misuse words and notation all the time without anyone arguing they're ridiculous.

That only indicates that you haven't found the many angry blog posts yet, not that they don't exist :)

The problem isn't really the ratio, but the use in arbitrary contexts that require a lot of pre-existing knowledge. The reference value is sometimes a rather arbitrary value in an arbitrary unit, neither of which is communicated by the "dB" unit suffix.

The SI way to write `10 dBm` is to write `10 dB (1mW)`, clearly communicating both the power level and the reference point and unit. This ensures that you do not have to just memorize a bunch of decibell suffixes and their magical reference values.

I have a feeling that a lot of people here haven't read the article. There's lots of "Its just a dimensionless ratio" comments

This sounds more like a problem with the 'real' world then.

In the "real world", techically competent people understand decibels just fine.

But this is not arcane knowledge only known by a priesthood. Since you are clearly confused about what a decibel is and how and why it is used, you can read

https://en.wikipedia.org/wiki/Decibel

and all will be revealed.

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