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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#411

Post by perching_aix »

davrosthedalek wrote: post #396
perching_aix wrote: post #379

Earlier quoted context omitted.

> Sometimes mega is squared as in megapixels. Is that right? A pixel is a 2D object already. It's not like e.g. with centimeters, where it's a 1D unit, so it becomes centimeters squared to form a 2D unit.

it's (cm)^2, not c(m^2). If there would be the one-dimensional equivalent to pixels, say pix, then 1pixel = 1pix^2, and then 1 megapixel = (kpix)^2

After putting significantly more effort than perhaps socially acceptable into this, I completely agree so far, but I'm still horribly confused about GP's point about "mega" being a "squared unit in megapixels".

That to me implies that "mega" in "megapixels" is a planar ("[pre?-]squared") scaling factor, but it's... not really? Are those even a thing?

I think this is what the debate is about at least. Mega does line up with kilo squared, but that's not because mega becomes a planar scaling factor, but because it just so happens that 1000 times 1000 is 1 million. It's kind of a coincidence? Like it's literally 1 million pixels, that's what's being meant. Just like with cm squared, the ohhhhhhhhhhhhhhhhhhhhhhhhh

Re: The scientific “unit” we call the decibel

#412

Post by JadeNB »

drob518 wrote: post #343
viraptor wrote: post #340

Earlier quoted context omitted.

There are two paths: "it was weird but then I got used to it, you're just ignorant" or "it was weird, I got used to it, but we should improve the situation". I know which side I want to be on. Even if it takes decades like the data SI prefixes.

You’re discounting familiarity as being stupid. The real path is “it was weird but once I spent some time with it, it made perfect sense.”

> You’re discounting familiarity as being stupid. The real path is “it was weird but once I spent some time with it, it made perfect sense.”

I don't think either of your parent's paths say that:

> There are two paths: "it was weird but then I got used to it, you're just ignorant" or "it was weird, I got used to it, but we should improve the situation". I know which side I want to be on. Even if it takes decades like the data SI prefixes.

I believe that they're saying that, yes, experts get used to it, after which it makes complete sense (as would any arbitrary but consistent convention, once you got used to it), but, in any living field, there will constantly be non-experts looking to become experts. If there is a way to make the process easier for them while not introducing any lack of precision that would hamper experts, then why not?

Re: The scientific “unit” we call the decibel

#413

Post by davrosthedalek »

perching_aix wrote: post #411
davrosthedalek wrote: post #396

Earlier quoted context omitted.

it's (cm)^2, not c(m^2). If there would be the one-dimensional equivalent to pixels, say pix, then 1pixel = 1pix^2, and then 1 megapixel = (kpix)^2

After putting significantly more effort than perhaps socially acceptable into this, I completely agree so far, but I'm still horribly confused about GP's point about "mega" being a "squared unit in megapixels". That to me implies that "mega" in "megapixels" is a planar ("[pre?-]squared") scaling factor, but it's... not really? Are those even a thing? I think this is what the debate is about at least. Mega does line u…

I believe the point is that in "centimeters squared" you also square the cm. So it's 1/100 of a meter, then squared. While the mega in megapixels applies to the area. So presumably there are two length multiplied to be a pixel, and then you have a million of those.

I don't think it's a very deep point, and I would say the mega is not squared, but the centi is squared.

Re: The scientific “unit” we call the decibel

#414

Post by beloch »

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!

Many scientific measurements are entirely contextual. e.g. What is 0 V? Ground? Is ground across the globe always at the same potential? Nope. What's ground on a space station? Ground potential is whatever we want it to be. You don't need to define what ground potential is in, say, a computer, relative to some global standard for things to work.

How about velocity? What's 0 m/s? What does it mean to be absolutely still? All motion is relative, and being still is entirely a matter of perspective. You might be sitting still on a train, but traveling very quickly relative to a cow standing still while you blow by.

Bels are a relative measure that confuse some because they pop up in different contexts that seem unrelated. However, they are useful when dealing with quantities for which most pertinent relationships are exponential. e.g. They work for sound because humans perceive exponential increases in volume in a linear fashion. Something that is 3dB louder is twice as loud in terms of pressure levels, but we only perceive it as a little bit louder. Sound pressure levels are both relative measures and an attempt to reflect human perception . That makes them, necessarily, a bit odd.

Re: The scientific “unit” we call the decibel

#415

Post by klodolph »

viraptor wrote: post #340
drob518 wrote: post #323

Earlier quoted context omitted.

That’s because you’re a casual observer. If you’re an audio engineer, recording things, designing microphones, amps, or speakers, then you’d know it. Trust me. I’m a digital electrical engineer (computer engineering, basically). I thought that dBs were weird, too. My dad worked in microwave communications systems for his career and dBs are perfectly natural for him. Ditto my daughter who is an audio engineer. Droppin…

There are two paths: "it was weird but then I got used to it, you're just ignorant" or "it was weird, I got used to it, but we should improve the situation". I know which side I want to be on. Even if it takes decades like the data SI prefixes.

What’s to improve? I think the situation works well for people who work in the fields that use dB.

Re: The scientific “unit” we call the decibel

#416

Post by klodolph »

viraptor wrote: post #336
drob518 wrote: post #325

Earlier quoted context omitted.

But it’s not. He’s raging against dB.

Yes. He's complaining against dB with no reference, not against dB(A) for example. (Apart from the naming of some of them being silly)

dB(A) is a weighting. It’s not a reference and it’s not units. I think some of the confusion here comes from people not actually understanding units.

A-weighting describes how different frequencies are summed up. It’s like saying “RMS”. RMS is not units, A-weighting is not units. You can apply A weighting to voltage, digital signals, or audio. They all have different units but can all be A-weighted.

You could invent a new unit for A-weighted audio, but you would need several.

Re: The scientific “unit” we call the decibel

#417

Post by mystified5016 »

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…

Exactly, the log(x) function is stupid and useless! It's the log of what? 6? Pi? Little-g? Same for logn(x). Who the hell is n?!

Re: The scientific “unit” we call the decibel

#418

Post by perching_aix »

davrosthedalek wrote: post #413
perching_aix wrote: post #411

Earlier quoted context omitted.

After putting significantly more effort than perhaps socially acceptable into this, I completely agree so far, but I'm still horribly confused about GP's point about "mega" being a "squared unit in megapixels". That to me implies that "mega" in "megapixels" is a planar ("[pre?-]squared") scaling factor, but it's... not really? Are those even a thing? I think this is what the debate is about at least. Mega does line u…

I believe the point is that in "centimeters squared" you also square the cm. So it's 1/100 of a meter, then squared. While the mega in megapixels applies to the area. So presumably there are two length multiplied to be a pixel, and then you have a million of those. I don't think it's a very deep point, and I would say the mega is not squared, but the centi is squared.

What finally clicked it into place for me was trying to perform a unit conversion. It's kind of annoying cause we don't really use mega with anything squared usually (I don't recall anything at the moment at least), which added to the confusion.

When one converts from square kilometers (km2) to square meters (m2), one needs to undo the kilo (x1000) not once, but twice, accounting for both dimensions. So as you say, it's actually here where the scaling factor is secretly squared, it's k2, just not written out. Hence despite kilo being a 1000x bump, you need to divide by 1 million, because it's actually squared in kilometers squared.

So if mega in megapixels was behaving "normally", that would imply similar semantics, so to convert into kilopixels, you'd divide by 1000 not just once, but twice. But no, 1 megapixels is 1000 kilopixels. I guess the idea is that instead of being "secretly" squared it's "explicitly" already "square" as a result? So instead of resolving to mega2 pixels2, it's just mega pixels, since pixels is 2D, and so squaring it is unnecessary.

I think I get it now at least, but yeah, I agree with your sentiment. It actually reminds me, when I first learned converting between units of area in primary school, I had quite the troubles with wrapping my head around it exactly because of this.

Re: The scientific “unit” we call the decibel

#419

Post by crazygringo »

regularjack wrote: post #241
skrebbel wrote: post #207

Earlier quoted context omitted.

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…

There is no such thing as full volume, and there is not such thing as zero volume.

I don't know what you're talking about. Both of those exist.

Zero volume is when a speaker's diaphragm is still. On an 8-bit PCM audio file, it corresponds to a value of zero.

In the context of a signal, full volume corresponds to the 127 value in an 8-but PCM audio file (or arguably -128). In the context of a speaker, those values should push the diaphragm no further than how far it can travel linearly without distortion. Obviously the user may want to turn down the volume from this full volume.

I hope you understand that even when using an audio editor that displays values in dB, the underlying values are integers (or floats) that absolutely have zero and "full volume" meanings, and conventionally map respectively to -∞ dB and 0 dB.

Re: The scientific “unit” we call the decibel

#420

Post by [deleted] »

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…

[deleted]
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