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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#161

Post by mousethatroared »

kazinator wrote: post #57

The confusing thing about decibels is not the Watts versus Volts thing. It is the following. If you mix two identical signals (same shape and amplitude) which are in phase, you double the voltage, and so quadruple the power, which is +6 dB. But if you mix two unrelated signals which are about the same in amplitude, their power levels merely add, doubling the power: +3 dB.

If they're identical and in phase, the addition is obviously a multiplication by 2 -> 6dB.

If they're unrelated the signals can also cancel out. So not 6bB. If not 6 dB then what is it? An integral that has already been solved for us :D

Re: The scientific “unit” we call the decibel

#162

Post by detourdog »

nomercy400 wrote: post #143
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…

Does that also work for showers, with mixing hot and cold water. I feel that a 1% change in the knob/balance goes from too cold to too hot.

Nothing to do with decibels but the thermostat on the water heater might be set too high. If one lowers the overall temperature the ratio of cold to hot will balance.

Re: The scientific “unit” we call the decibel

#164

Post by verzali »

Sharlin wrote: post #31
rebolek wrote: post #3

While the author is technically right, I must argue that in the area of sound work, decibels make sense. Zero is base level, -3db is half loudness, +3dB is double. There may be a better way to describe loudness, but decibel is good enough.

> -3db is half loudness Sure, perfect sense.

10*log10(0.5) = -3

That's the math of it.

Re: The scientific “unit” we call the decibel

#165

Post by jononor »

jfengel wrote: post #158
KeplerBoy wrote: post #108

Earlier quoted context omitted.

We have a unit for that. It's dBm and very easy to grasp. 0 dBm is 1 mW, every 10 dBm is an order of magnitude more (10 dBm = 10 mW). dB is only confusing if people omit which quantities they are relating. If it's clear like in the case of dBm which relate to 1 mW, it's an awesome tool.

Unfortunately, people omit the quantities all the time. Domain experts assume it when talking to each other, and non-experts repeat it without knowing that it refers to anything at all. (I still don't really know what it means for a sound to have "decibels".)

When referring to sound in the physical world, "decibel" mean dB SPL (sound pressure level). Which is defined as the ratio to the smallest perceivable sound pressure level. Unfortunately that is still a bit underspecified, it may be measured with a frequency weighting like A weighting. And then there is the integration time or other temporal aggregation, but that is separate from decibel/log.

When in analog audio, it usually means dbV, relative to a reference voltage.

And in digital audio, usually dBFS - relative to the maximum amplitude that can be represented.

Re: The scientific “unit” we call the decibel

#166

Post by rcxdude »

kristjank wrote: post #33

This seems exceedingly ignorant of the work decibels do in telecommunications, RF and fibre engineering. The voltage vs power relationship is something that exists and is a core memory of beginner blunders in the field, but it boils down to a simple 10 vs 20 division operation. Besides that, the decibel simplifies a lot of multiplying very small and very big numbers to summing of two-digit numbers that you can do in…

I work in a related field (lots of signal processing, but not necessarily RF-y or audio-y), and it's a constant source of confusion. I actively avoid using them in technical communication because they will be misinterpreted by someone, and when we have customers who use them they usually don't actually know enough context to disambiguate them.

Re: The scientific “unit” we call the decibel

#167

Post by mapt »

kristjank wrote: post #33

This seems exceedingly ignorant of the work decibels do in telecommunications, RF and fibre engineering. The voltage vs power relationship is something that exists and is a core memory of beginner blunders in the field, but it boils down to a simple 10 vs 20 division operation. Besides that, the decibel simplifies a lot of multiplying very small and very big numbers to summing of two-digit numbers that you can do in…

Having a logarithmic scale is a very different feature than having this one symbol to express all logarithmic scales with contextual meanings that sometimes need to be incorporated as two or three separate variations in a conversation.

Why wouldn't this work better broken out as half a dozen different units, with objective zero points and mathematical convertibility?

Re: The scientific “unit” we call the decibel

#168

Post by ajuc »

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…

Logarithmic scale aligns with human experience.

OP isn't criticizing logarithmic scale in general but dB in particular.

If dB in particular aligned well with human experience - volume knobs would be labeled with dB values instead of 1-11.

Re: The scientific “unit” we call the decibel

#169

Post by svara »

TheOtherHobbes wrote: post #119
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…

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 potential in Volt.

And then you've got the cases where it really just is a ratio (one of two possibilities).

You'll see all of these called "decibels".

You see why people are irritated?

Re: The scientific “unit” we call the decibel

#170

Post by losvedir »

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…

Nothing in the article and nobody in the comments takes issue with the fact that it's logarithmic. It's everything else that's the problem. (It's a ratio where the base value is situation dependent, and the base of the logarithm varies.)
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