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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#231

Post by anilakar »

numpad0 wrote: post #179

I just can't understand why "[specialized domain] uses these stupid wrong units, it should be [unit that no educated smart SMEs use]" types don't do their researches to understand why those are used at all. This type of weird non-SI units appear when means of measurement and unit is related to one another and has downstream dependencies. Just look at aviation. An airplane's: - speed is measured in knots, or minute of…

Wait until you hear about unit conversions in aeronautical mental math. 1 NM across ground corresponds to 1000 or 100 feet of altitude in many conversion formulas. For small angles, sines and tangents are approximated by degrees of azimuth × distance in NM = 60.

Re: The scientific “unit” we call the decibel

#232

Post by detourdog »

rusk wrote: post #218
detourdog wrote: post #162

Earlier quoted context omitted.

Nothing to do with decibels but the thermostat on the water heater might be set too high. If one lowers the overall temperature the ratio of cold to hot will balance.

You are bounded by a minimum floor for the hot water. Below a certain point you can get legionnaires. To me it seems like one of two things: external pressure between hot and cold is mismatched so a small change to one side overwhelms the weaker flow. Alternatively it might just be a broken or poor quality mixer that isn’t providing the appropriate ‘nuance’ of control, and that may indeed be expressed as some sort of…

The thermostat could still be set too high. I think you might be overstating the dangers of legionnaires.

It also a simple thing to check and would be the first step in my troubleshooting routine for this complaint.

Here is a link describing the dangers.

https://www.heatgeek.com/hot-water-temperature-scalding-and-...

Re: The scientific “unit” we call the decibel

#233

Post by ants_a »

megous wrote: post #177
gwd wrote: post #148

Earlier quoted context omitted.

> Aspect ratio is a ratio. Right, but in this case they only give you one of the two numbers. Imagine being told that your TV had an aspect ration of ":16", and you just have to magically know what the other number means in the context. And sometimes ":16" actually means ":4", because quadratic mumble mumble, and sometimes the number is scaled according to some other "how big it seems to humans" factor; all of which…

Ratio is just a single number. 4:3 can be expressed as 1.3333~ and it just says how much bigger one number is compared to another. RE: Yes, I was able to read and understand the article. I also have 8 years of EE. Ratio is still a single number in the end. You can have an actual size of a monitor 1600 x 1200 and the ratio of sides is 1600/1200, which is just a single number. You can express it in multiple ways. You s…

So my display aspect ratio is 2.5dB. Or is it 5dB because it's not measuring power?

Re: The scientific “unit” we call the decibel

#234

Post by klodolph »

sanderjd wrote: post #200
lambdaone wrote: post #187

It's a bit like hating numbers, and saying "What do you mean by 'three'; what is it - three volts, three amps, three metres? Clearly 'three' is meaningless, and we should stop using it and all the other numbers besides." decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity. In every context where decibels are used, either the unit they qualify is explicitly speci…

> 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.

Re: The scientific “unit” we call the decibel

#235

Post by [deleted] »

sanderjd wrote: post #200
lambdaone wrote: post #187

It's a bit like hating numbers, and saying "What do you mean by 'three'; what is it - three volts, three amps, three metres? Clearly 'three' is meaningless, and we should stop using it and all the other numbers besides." decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity. In every context where decibels are used, either the unit they qualify is explicitly speci…

> 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!

[deleted]

Re: The scientific “unit” we call the decibel

#236

Post by klodolph »

hgomersall wrote: post #201
weinzierl wrote: post #193

Earlier quoted context omitted.

"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 w…

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.

Re: The scientific “unit” we call the decibel

#237

Post by colejohnson66 »

HPsquared wrote: post #220

It's a bit like "percent". A shorthand for dealing with ratios, often with hidden assumptions.

Sure, but you never say "the production is at 50%". 50% of what? Peak possible output? Typical output? That's what the author's complaint is: dB, while arguably useful, is annoying because people leave out the part that it's relative to. And then people, when talking about dB, assume the other party has knowledge of what their ratio is relative to. dBm, dbSPL, etc.

Re: The scientific “unit” we call the decibel

#238

Post by sgarland »

TheOtherHobbes wrote: post #119
svara wrote: post #62

Earlier quoted context omitted.

> 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 usef…

> The units are implied by the context.

This is the absurd part. There do exist other ratios that masquerade as units, e.g. specific gravity, and its meaning also changes depending on what you’re using it for - liquids are compared to pure water at 4 C, gases are compared to air at 20 C. As the parent comment points out, you can get used to things with experience. That doesn’t make them any less absurd. Look at Fahrenheit, for example. I’m American, and I still think it’s absurd, but because I’m extremely used to it, it feels natural.

Re: The scientific “unit” we call the decibel

#239

Post by nyeah »

skrebbel wrote: post #207
lambdaone wrote: post #187

It's a bit like hating numbers, and saying "What do you mean by 'three'; what is it - three volts, three amps, three metres? Clearly 'three' is meaningless, and we should stop using it and all the other numbers besides." decibels are simply a dimensionless ratio, used as a multiplier for some known value of some known quantity. In every context where decibels are used, either the unit they qualify is explicitly speci…

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…

It makes perfect sense that the sliders start at 0dB and go down to -inf. Maybe you don't understand it, but it definitely makes sense. Everyone who uses dB has also tried a % scale with 100% as 0dB, and then later made a conscious choice to figure out how dB work.

Maybe they're all in a conspiracy to make things needlessly complex. But that's not the only possibility.

Re: The scientific “unit” we call the decibel

#240

Post by weinzierl »

hgomersall wrote: post #201
weinzierl wrote: post #193

Earlier quoted context omitted.

"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 w…

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.

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.
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