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

91–100 of 511 posts

Re: The scientific “unit” we call the decibel

#91

Post by roelschroeven »

atoav wrote: post #21

But dB is not a unit, it is a multiplier. dB on its own is unitless and if we say "X is reduced by 6 dB" you know that the value of X is half of what it was before (×0.5) if something is amplified by 6 dB it is double of what it was before (×2.0)¹ Note that the unit only starts to play a role when you reference your dB value to some absolute maximum, e.g.: dBV which is referenced to 1V RMS dBu which is referenced to…

> If you use dB to describe the power of a signal that is slightly different (you use 10 instead of 20 as multiplier/divisor)

This is the part I don't get. This is the part where "dB is just a multiplier" falls short. It's there to "so that the related power and root-power levels change by the same value in linear systems" (that's how Wikipedia formulates it). Why is that even something you would want? Isn't it much more logical, intuitive, consistent and useful to reflect the fact of power being proportional to the square of the signal in it having double the dB value?

Re: The scientific “unit” we call the decibel

#93

Post by IsTom »

rusk wrote: post #84
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…

dB for sound in particular aligns with human experience. The (10 -) 1-10 on a volume knob typically aligns with a logarithmic scale because we hear differences in loudness at an order of magnitude. A linear volume knob would be frustratingly useless as you would have to crank it many many many times the higher up you want to go. Presumably hundreds of times. A traditional pot couldn’t do that of course but maybe you…

You could have log Watts or something, it doesn't have to be dB to be logarithmic.

Re: The scientific “unit” we call the decibel

#94

Post by taneq »

rusk wrote: post #84
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…

dB for sound in particular aligns with human experience. The (10 -) 1-10 on a volume knob typically aligns with a logarithmic scale because we hear differences in loudness at an order of magnitude. A linear volume knob would be frustratingly useless as you would have to crank it many many many times the higher up you want to go. Presumably hundreds of times. A traditional pot couldn’t do that of course but maybe you…

Ever have a cheap set of external speakers that got super loud in the first quarter turn of the volume knob but were pretty much the same loudness after that? Yeah, linear pot for the volume knob.

No need for an encoder and software, though, logarithmic pots are readily available for precisely this reason. :)

Re: The scientific “unit” we call the decibel

#95

Post by IsTom »

mikewarot wrote: post #68
rocqua wrote: post #51

Earlier quoted context omitted.

Decibels in gain, those are fine. Though they use a silly base. dBm makes a decent amount of sense, given the RF background. The fact that decibels work differently for voltage and power is very weird, but understandable in isolation. But audio decibels are horribly underspecified. And any other use of a decibel as a dimensionful unit is horrible. I think the RF people know, and that's why they use dBm. Any system th…

Decibels aren't units... they are ratios. The ratio could be gain, or loss, or compared to the noise floor, or the signal of interest, or a standard unit, such as Watts, milliWatts, or microVolts into 50 ohms. >The fact that decibels work differently for voltage and power is very weird, but understandable in isolation. If you have a given load, increasing the voltage by a ratio of 10:1 (20 dB) is exactly the same as…

> Decibels aren't units... they are ratios.

Until they are a ratio to a specific arcane reference level as mentioned in the article.

Re: The scientific “unit” we call the decibel

#96

Post by rusk »

IsTom wrote: post #93
rusk wrote: post #84

Earlier quoted context omitted.

dB for sound in particular aligns with human experience. The (10 -) 1-10 on a volume knob typically aligns with a logarithmic scale because we hear differences in loudness at an order of magnitude. A linear volume knob would be frustratingly useless as you would have to crank it many many many times the higher up you want to go. Presumably hundreds of times. A traditional pot couldn’t do that of course but maybe you…

You could have log Watts or something, it doesn't have to be dB to be logarithmic.

That would be dishonest. You don’t adjust input power - you adjust attenuation

EDIT if you did let’s say approximate power, or measure and present the consumed power (as some systems do) you would still be in a situation about how to present this data. Do you present your users with a simple 1-10 (logarithmic) or a 10 digit display which sweeps over vast ranges of uninteresting values.

If you opted for a more compact scientific notation … well guess what that’s also logarithmic but in two parts LOL

Re: The scientific “unit” we call the decibel

#97

Post by timewizard »

bigiain wrote: post #23
timewizard wrote: post #12

> That said, I don’t know how to pronounce “3e5” "Three to the exponent of five." Or "Three Exponent Five." Or "Three Exp Five." > Seeing this, some madman decided that 1 bel should always describe a 10× increase in power, even if it’s applied to another base unit. This means that if you’re talking about watts, +1 bel is an increase of 10×; but if you’re talking about volts, it’s an increase of √10× This is power vs.…

> > That said, I don’t know how to pronounce “3e5” > "Three to the exponent of five." Or "Three Exponent Five." Or "Three Exp Five." Somehow, you need to distinguish between 3^5 (=243), 3 x e^5 (=~445.24), and 3 x 10^5 (=300,000). I'd pronounce "3e5" and "three times ten to the 5" in most cases.

> 3^5 (=243)

Three to the power of five.

> 3 x e^5

Three times the fifth power of e. Or Three times e's fifth power.

> 3 x 10^5 (=300,000).

Three to the exponent of five.

A calculator user once suggested "decapower." I think exponent and "EXP" are comfortable and easy to say and are ingrained to most old school calculator users. Which is also why I think "e's fifth power" can be a more natural sequence.

Re: The scientific “unit” we call the decibel

#98

Post by badlibrarian »

thaumasiotes wrote: post #87
badlibrarian wrote: post #71

Horsepower is a unit of measurement. There's hp and bhp and hpE and... "Other names for the metric horsepower are the Italian cavallo vapore (cv), Dutch paardenkracht (pk), the French cheval-vapeur (ch), the Spanish caballo de vapor and Portuguese cavalo-vapor (cv), the Russian лошадиная сила (л. с.), the Swedish hästkraft (hk), the Finnish hevosvoima (hv), the Estonian hobujõud (hj), the Norwegian and Danish hestekr…

> "Other names for the metric horsepower are [...]" I'm not clear on what point you think you're making. Is it interesting that the same thing might have different names in different languages? That subsection of the article, by the way, is obviously lying: > The various units used to indicate this definition (PS, KM, cv, hk, pk, k, ks and ch) all translate to horse power in English. cv and ch translate to steam hors…

That a unit of power has a dozen metric abbreviations and converts to watts at different values depending on what it is measuring (and when) is precisely the point.

Decibels aren't ridicluous or a unit of measure. Horsepower, however...

Re: The scientific “unit” we call the decibel

#100

Post by hashhar »

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…

This is exactly it. The people who get confused by decibels are treating it a unit in it's own right when it's really just a ratio of some unit.
Post reply on HN