Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

The scientific “unit” we call the decibel

lcamtuf.substack.com

Post reply on HN
Print view View original

181–190 of 511 posts

Re: The scientific “unit” we call the decibel

#181

Post by rcxdude »

mikewarot wrote: post #75
rocqua wrote: post #66

Earlier quoted context omitted.

> But dB is not a unit, it is a multiplier. dB on its own is unitless. The point of the article is exactly that this should be the case. But it ends up not being the case. Mostly because people use dB with reference to some assumed baseline. But also because a 20db change could be a 10x change conpared to baseline, or a 100x change compared to baseline, depending on what unit you are measuring in.

20 dB is always the same, actually. If you multiply voltage (and thus current as well) by 10:1 (20 db) the power is multiplied by 100:1 (also 20 dB)

That's the point that's confusing. Especially in contexts where it's not obvious whether it's power-like or amplitude-like. It should be 40dB of power gain or 20dB of amplitude gain, with the context made explicit.

Re: The scientific “unit” we call the decibel

#182

Post by [deleted] »

stephen_g wrote: post #151
nabla9 wrote: post #109

Decibel is ridiculously overloaded concept. It can be used to express and calculate relative change in power, amplitude ratios, and absolute change. All of these are different units and should always use different notation, but sometimes it's skipped.

But a lot of them can be combined - like you can take dBm of a microwave signal going into a filter, subtract the dB figure of loss through a filter, add the dB figure of gain through an amplifier, then add the dBi of antenna gain, and get a meaningful number (equivalent isotopic radiated power or EIRP, in dBm) out the end! It’s quite amazing!

[deleted]

Re: The scientific “unit” we call the decibel

#183

Post by jononor »

coolcase wrote: post #39
hock_ads_ad_hoc wrote: post #20

The author seems confused. Decibels aren’t units. They’re a way to express a ratio between a reference value and some other value. They’re used where they are useful.

They are units too. When you have regulations relating to sound they will say how many dB the limit is.

No they will specify something like dB SPL, A-weighted with Fast time integration. Sometimes referred to as dB(A) SPL. And measured with a particular method, which specifies things like distance from sources, environmental conditions, etc.

Re: The scientific “unit” we call the decibel

#184

Post by Severian »

mattmanser wrote: post #105
rusk wrote: post #101

Earlier quoted context omitted.

No I’ve never had one of those LOL Pots do log and lin scales but they only have a limited angular range.

I've actually noticed this two days ago with some bluetooth headphones and my phone. The volume control on my android phone was acting just like this when my headphones were connected. When changing the volume with the phone only a small section of the bottom quarter of the volume control actually made a difference, but the volume controls on the headphone themselves were acting "normally". Usually the phone volume i…

I've had the same issues as you, and here are some things I've done or tried as a remedy.

Try going into Android "Developer options" and enable the option "Disable Absolute Volume". Some devices cannot handle the way Android maps the "master" volume of the system to Bluetooth. With the option enabled you will have a separate slider to adjust the Bluetooth volume, and the volume buttons will instead only control the "Media" volume.

An alternate thing to do is under the same Developer Options is instead of disabling Absolute control is to change the Bluetooth AVRCP version to at least v1.5. v1.5 AVRCP introduces the Absolute Volume control functionality.

But, it could also be what you may have are Bluetooth devices that do not support Absolute Volume, or lack AVRCP v1.5 compatibility. If none of this works, I suggest purchasing the "Precise Volume 2.0 + Equalizer" app. I use this as it gives you more fine-grained control over the number of steps in the volume slider (for example, I now have 100 steps). It also allows you to calibrate the number of steps to a specific device, so you can literally change how many steps from quiet to loud. It's worth all of the $10 it costs, and has other nice quality of life features as well.

Re: The scientific “unit” we call the decibel

#185

Post by tim333 »

The author gives the downsides but not the upside of why it is like that.

It's basically so it describes sound levels on an understandable scale with 0db being just audible and 100dB being very loud.

It also corresponds to the energy carried by the sound - 0 dB is 1 pW per square meter so it is kind of a scientific unit. It's probably easier to have a measure that is understandable by the public and let engineers do conversion calculations for signal levels in networks than the other way around.

Re: The scientific “unit” we call the decibel

#186

Post by cb321 »

Abbreviation confusability is relative to { in fact one might say measured by ;-) - number? entropy? etc. } the listener/reader's knowledge/exposure, much as sound levels need a reference distance.

I have heard "bare K" refer to a great many different things, not just kilobits (transmission) or kilobytes (storage) or kilograms (drug trade) or kilometers (foot races) and on & on, but pages or items or etc.

The fundamental problem is that some humans like to abbreviate while others get caught and annoyed by the necessary ambiguity of such abbreviation. Sometimes this can be the very same human in different contexts. ;-)

In fact, there even seems to be some effect where "in the know people" do this intentionally - like kids with their slang - as a token of in-group membership. And yes, this membership is at direct odds with broader communication, by definition/construction. To me this article seems to be just complaining about "how people are". So it goes!

This is the primary complaint. The secondary one about voltage and power and the ambiguity of the prefix itself was addressed in another comment (https://news.ycombinator.com/item?id=44059611).

Re: The scientific “unit” we call the decibel

#187

Post by lambdaone »

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 specified, or the unit is implicity known from the context. For instance, in the case of loudness of noise to human ears in air, the unit can be taken to be dBA (in all but rare cases which will be specified) measured with an appropriate A-weighted sensor, relative to the standard reference power level.

And similar (but different) principles apply to every other thing measured in dB; either theres an implicit convention, or the 0 dB point and measurement basis are specified.

People who assume that everyone is an idiot but themselves are rarely correct.

I look forward to the author discovering about (for example) the measurement of light, or colorimetry, and the many and various subtleties involved. The apparent excessive complexity is necessary, not invented to create confusion.

Re: The scientific “unit” we call the decibel

#188

Post by gwd »

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…

Sure, and 10db means "10x more power". But:

1. 10x more power than what? It changes, and you Just Have to Know.

2. It's 10x more power; so if you're measuring power, like pascals, then 10db means 10x more pascals. But if you're measuring something like voltage, then it's not 10x more voltage, it's something else.

3. And if you're talking about sound, you may be talking about objective power; or you might be talking about how much more powerful it seems to humans.

Re: The scientific “unit” we call the decibel

#189

Post by wisty »

svara wrote: post #169
TheOtherHobbes wrote: post #119

Earlier quoted context omitted.

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…

Respectfully, I'm not sure you fully understand how dB is used. The analogy to aspect ratios only works for one of multiple uses of decibel. dB SPL and dB(A) are not ratios, they're absolute. You can derive them from a ratio and a reference level, but the former can be expressed in Pascal and the latter relates to Pascals after applying a perceptual correction function. Similarly, dBm can be expressed as an absolute…

Yep you have dB for a ratio, and dB SPL as a physical unit. Just as the article says.

And yeah, the issue is when people forget to use physical units, like if they say it's 30 degrees outside amd not saying C F or K or latitude.

The historical context is a bit meaningless as well since the main application for the OG dB is 101 classes.

Re: The scientific “unit” we call the decibel

#190

Post by dagw »

gwd wrote: post #148
TheOtherHobbes wrote: post #119

Earlier quoted context omitted.

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…

> 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…

Imagine being told that your TV had an aspect ration of ":16"

We kind of have that with people talking about a screen or image being "2k" and then expect you to infer what the actual resolution and aspect ratio is from context.

Post reply on HN