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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#431

Post by BlueTemplar »

StableAlkyne wrote: post #380
teknopaul wrote: post #369

"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." Were were here recently with "mega": Sometimes mega is squared as in megapixels. Sometime not as in megabytes. No biggie. Db in audio is a relative scale and that makes perfect sense. If you mixer goes + or - 6db that makes sense but can't be measured as power, your mixe…

> Sometimes mega is squared as in megapixels. Sometime not as in megabytes. Even worse is Mega in Megabytes could be 1,000,000 or 1,048,576 and it's more or less up to you to know what's what (Yeah, there are formally megabytes/mebiibytes/MiB/MB, but I honestly cannot recall the last time I heard anyone use anything other than just "megabyte" for 2^20 bytes... Or even wanted to refer to exactly 1,000,000 bytes. Other…

Wait, when did they stop ?!

Re: The scientific “unit” we call the decibel

#432

Post by relaxing »

davrosthedalek wrote: post #346
relaxing wrote: post #174

Earlier quoted context omitted.

You should have a legitimate question as to what dB’s the amp is referring to. What brand and model is it? First, is it actually specified as dB’s? Most amps I’ve seen display volume on an arbitrary scale, no units specified. Second, the amp has no way to know dB sound pressure, as that depends on the rest of signal chain. So is the displayed figure referring to dBu, dB mV, something else, or something totally bunk?

If 0 dB is its maximum, then -50dB is 50 dB down in power from its maximum (so 10^-5). No m V or other post-fix needed.

That’s true but not that helpful for determining what your ears actually hear.

Re: The scientific “unit” we call the decibel

#433

Post by lxgr »

perching_aix wrote: post #427
lxgr wrote: post #291

Earlier quoted context omitted.

> A lot of them would actually agree with the article, but historical sometimes wins Indeed – as evidenced by some parts of the world still using non-metric units in daily life or even engineering :)

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.

When the Euro was introduced, I've heard people say things like "older generations will never adapt to the new currency, they'll always refer to the old denominations in their head" – which turned out to be completely untrue.

Adapting to new units is very possible, but it needs a concerted effort. Absent a good inherent reason or anybody capable of artificially creating one, it won't happen on its own.

Re: The scientific “unit” we call the decibel

#434

Post by lxgr »

hgomersall wrote: post #295
lxgr wrote: post #281

Earlier quoted context omitted.

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 :)

Re: The scientific “unit” we call the decibel

#435

Post by vt240 »

I see dB scale units used without contextual issues in near uniformity. Unfortunately, I have to agree with the OP, that microphone capsule manufactures seem to be an edge case. I'm not sure where dBV/Pa became the standard. I can understand why given 94dBSPL@1000Hz calibration standards, and the measurement equipment of the time, but I've run into my own fair share of datasheets with lines such as 'Sensitivity -45dB' with no units or other call outs for the standard in use. Thankfully, it seems like most modern datasheets use mV/Pa which seems like a much better unit in my book.

Re: The scientific “unit” we call the decibel

#436

Post by blackguardx »

modeless wrote: post #326
severusdd wrote: post #76

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…

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.

Re: The scientific “unit” we call the decibel

#437

Post by nfriedly »

perching_aix wrote: post #427
lxgr wrote: post #291

Earlier quoted context omitted.

> A lot of them would actually agree with the article, but historical sometimes wins Indeed – as evidenced by some parts of the world still using non-metric units in daily life or even engineering :)

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.

Using the diagonal to measure the size of a display is also a bit weird because it doesn't compare well across aspect ratios. A 34 inch 21:9 ultrawide is actually smaller (in terms of area) than a 32 inch 16:9 display.

Re: The scientific “unit” we call the decibel

#438

Post by BlueTemplar »

HPsquared wrote: post #220

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

Insert mandatory complaint about percentages being misused : their point is the approximation : 1.02×1.03~1.05 +2%+3%~+5%, which only holds up to low tens +/-%.

Re: The scientific “unit” we call the decibel

#439

Post by djhn »

lxgr wrote: post #433
perching_aix wrote: post #427

Earlier quoted context omitted.

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.

When the Euro was introduced, I've heard people say things like "older generations will never adapt to the new currency, they'll always refer to the old denominations in their head" – which turned out to be completely untrue. Adapting to new units is very possible, but it needs a concerted effort. Absent a good inherent reason or anybody capable of artificially creating one, it won't happen on its own.

Did it? I feel like 60+ year olds (current age) mostly still convert (bonus points for not accounting for inflation)

Re: The scientific “unit” we call the decibel

#440

Post by nyeah »

lifthrasiir wrote: post #430
nyeah wrote: post #425

Earlier quoted context omitted.

...unless we're talking about a unitless ratio, like "this has 10dB less power than that". Which happens a lot.

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.

It's correct to use dB without a suffix to indicate a pure ratio. (It's ok if some people don't see why that's correct. That's acceptable.)

Nobody (I hope) says that 100mW is "10 dBm" more than 10mW. That would be wrong. Readers would be confused. Most people would cross their fingers and correct it to "10 dB", but who knows what it might mean?

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