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The scientific “unit” we call the decibel

lcamtuf.substack.com

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Re: The scientific “unit” we call the decibel

#451

Post by sanderjd »

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.”

No, it doesn't make perfect sense. It's a bad practice to leave off units. You just got used to it and seem to have developed pride in being in the in-crowd of people comfortable with an unclear jargon, and that has now blinded you to a bad status quo. Many such cases!

Re: The scientific “unit” we call the decibel

#452

Post by sanderjd »

klodolph wrote: post #415
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.

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

The improvement would be to specify the units you're working with, as is well known best practice in all science and engineering disciplines.

Re: The scientific “unit” we call the decibel

#453

Post by sanderjd »

davrosthedalek wrote: post #385
viraptor wrote: post #336

Earlier quoted context omitted.

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)

But dB without reference makes sense in many many occasions. Either because the reference is implicit (not ideal, but we have many implicit assumptions in communication), or because it's genuinely a ratio. Attenuation, gain. If you every find an "official" written document that uses dB not as attenuation/gain and is not specifying the reference (at least in a footnote), it's written either by idiots or for idiots, or…

No it doesn't. It's always bad for the actual unit to be implicit.

Re: The scientific “unit” we call the decibel

#454

Post by sanderjd »

beloch wrote: post #414
sanderjd wrote: post #200

Earlier quoted context omitted.

> 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 sti…

None of these other examples are contextual in the same way.

Re: The scientific “unit” we call the decibel

#455

Post by mitthrowaway2 »

davrosthedalek wrote: post #391
lifthrasiir wrote: post #40

The only thing you should know is that any use of bel and thus decibel should ideally have the reference level suffixed (usually in parentheses or subscript), not implied. The absolute sound pressure level is dB(SPL). The human-perceived loudness level is dB(A) and similar. The RMS voltage expressed in power is dB(u) (formerly dB(v), not same as capital dB(V)). And so on. And then each different instance of dB unit i…

That is of course not true. dB without reference is perfectly fine to use for gain and attenuation. dBm or any of the variants would be flat out wrong.

Even then, you'll get different results if it's 10 dB of voltage gain or 10 dB of power gain. You need to know what the actual units are.

Re: The scientific “unit” we call the decibel

#456

Post by creeble »

globular-toast wrote: post #64
kazinator wrote: post #26

Earlier quoted context omitted.

But, no! -3dB is half power, not half loudness. -3dB down is just slightly less loud.

Exactly. There's no way +3dB is perceptibly twice as loud. That's easy to test for yourself. +10dB is roughly twice as loud.

The BBC used to teach +6dB for twice as loud for music sources, but they've always been a bit conservative.

Re: The scientific “unit” we call the decibel

#457

Post by creeble »

relaxing wrote: post #432
davrosthedalek wrote: post #346

Earlier quoted context omitted.

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.

For music, they hear about 10dB is half/twice as loud.

Re: The scientific “unit” we call the decibel

#459

Post by BlueTemplar »

kazinator wrote: post #407
paipa wrote: post #216

Earlier quoted context omitted.

The denominator isn't the issue. The context-dependent base of the logarithm is, which makes 1 Bel = 10x for some things and 1 Bel = 3.16x for others. I've never heard of decibels used in probability theory. Did they adopt it with the same baked-in bastardizations? Please tell me +10dB(stdev) = +10dB(variance) isn't a thing.

(Funny you should mention that because while writing my grandparent comment above I vaguely ruminated about some kind of example involving standard deviation and variance, due to those being linked by squaring.) Even if there isn't a +10dB(stddev), logarithmic graphs are a thing, in many disciplines. You just refer to the axes as "log ". Any time you are dealing with data which has a wide dynamic range, especially wi…

One parallel comment mentions 'octaves' being used for that.

Re: The scientific “unit” we call the decibel

#460

Post by mcnamaratw »

mitthrowaway2 wrote: post #455
davrosthedalek wrote: post #391

Earlier quoted context omitted.

That is of course not true. dB without reference is perfectly fine to use for gain and attenuation. dBm or any of the variants would be flat out wrong.

Even then, you'll get different results if it's 10 dB of voltage gain or 10 dB of power gain. You need to know what the actual units are.

No, dB are always power gain.
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