| ▲ | sanderjd 2 days ago |
| > 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! |
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| ▲ | drob518 2 days ago | parent | next [-] |
| Just because the author is ignorant of the context doesn’t mean that the engineers working in those fields are. They use it because it all makes sense in context. |
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| ▲ | LastTrain 2 days ago | parent | next [-] | | Yeah hence his comment “If you know you know.” The author is far from ignorant on the subject, he’s pointing out the unit is often used without context. | | |
| ▲ | hulitu a day ago | parent [-] | | [flagged] | | |
| ▲ | marcosdumay a day ago | parent [-] | | You may have missed the short article explaining how it could mean 3 different things in an audio context, or 3 other different things in a radio context. Or how it doesn't actually mean anything by itself and yet people insist on using it that way. |
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| ▲ | Nevermark a day ago | parent | prev | next [-] | | The point of units is to indicate both what dimension, and relative magnitude in that dimension, is being talked about clearly. In virtually any other situation, leaving off units and counting on context to fill them in would be considered to be at the extreme end of unacceptable. The unit problems in question, are only accepted because they are an historically created anomaly. Not because they are a good idea, or anyone wanted that outcome. | |
| ▲ | sanderjd 2 days ago | parent | prev [-] | | This is literally the same as saying that you don't need to explicitly specify units in any field because "it all makes sense in context" to "engineers working in those fields". No. We've painstakingly figured out the right answer to this through the generations of doing science and engineering: You always specify units. | | |
| ▲ | drob518 2 days ago | parent [-] | | But obviously we don’t. So, there’s your counter proof. | | |
| ▲ | strbean 2 days ago | parent | next [-] | | Except the various disasters caused by assuming the wrong units (Mars Climate Orbiter, for example). | | |
| ▲ | monster_truck 2 days ago | parent | next [-] | | The team that wrote their code in English units instead of Metric defied specifications, that has nothing to do with this. > The Software Interface Specification (SIS), used to define the format of the AMD file, specifies the units associated with the impulse bit to be Newton-seconds (N-s). Newton seconds are the proper units for impulse (Force x Time) for metric units. The AMD software installed on the spacecraft used metric units for the computation and was correct. In the case of the ground software, the impulse bit reported to the AMD file was in English units of pounds (force)-seconds (lbf-s) rather than the metric units specified. From https://llis.nasa.gov/llis_lib/pdf/1009464main1_0641-mr.pdf | | |
| ▲ | seanhunter a day ago | parent [-] | | Hey don't blame the English for that. I would be prepared to wager you couldn't find a single English engineer who uses lbfs or anything similar. Everyone in physics or engineering uses metric for everything to do with forces even those who might use mph for a speed informally. | | |
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| ▲ | drob518 2 days ago | parent | prev [-] | | Which proves what? That misunderstandings happen? Yes they do. Get over it. But most amplifiers and recordings don’t crash and burn, so there’s your counter proof. Use units when they might be ambiguous. But in many fields they aren’t. | | |
| ▲ | Nevermark a day ago | parent | next [-] | | > But in many fields they aren’t. I am lost. What fields you are talking about? 1. I am unaware of any field operating within its own echo/context chamber using unit-less numeric notation for anything but actual unit-less quantities. Except for informal slap-dash arithmetic, on trivial calculations. 2. Units indicate the dimension being measured, not just the relative magnitude within that dimension. Nobody is going to know from any shared context, except in person, what a bare number measures. 3. Virtually every measurable quantity has multiple possible units of different relative magnitude, depending on micro context, so even people within a field, who agree on the dimension measured, still need units. Meters, light years, AU, angstroms? 4. You cannot apply standard formulas of physics, or anything else, without specific units. Formulas operate on dimensions, but to interpret and calculate any numbers, you need to know the specific unit being used for each dimension. (In any context, but a late night napkin argument between two well acquainted colleagues in a bar, units are universally used. And in that case, the opportunity for serious misunderstandings is more likely to be from missing units, than the quantity of scotch each has imbibed, or how much they have spilled on the napkin.) | | |
| ▲ | drob518 a day ago | parent [-] | | You’re arguing both sides. If nobody does it then it’s not a problem. |
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| ▲ | ashoeafoot a day ago | parent | prev [-] | | No, this are the sounds of underspecification. |
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| ▲ | sanderjd a day ago | parent | prev [-] | | The meaning of my last sentence is "You (should) always use units (or else there will inevitably be some mistake eventually due to confusion about the units)". |
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| ▲ | klodolph 2 days ago | parent | prev | next [-] |
| Sure, but the author is wrong. “How old is your son?” “He’s 3.” Clear in context. People write things like dB SPL (A-weighted) in spec sheets because spec sheets benefit from being unambiguous. Most of the time it’s really clear, like you’re talking about insertion loss or amplifier gain and there’s only one reasonable way to interpret it. |
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| ▲ | timeinput a day ago | parent | next [-] | | But for insertion loss and amplifier gain it is "just" dB, it's the ratio of the input to the output. The amplifier has a gain of 35 dB means its output is 35 dB higher than the input. If the input is -30 dBm the output is +5 dBm, etc. The reference for an amplifier, or insertion loss is clear in context since you're talking about the gain / loss of a device, and isn't referenced to any fixed scale like db relative to 1 mW, SPL (A-weighted), or 1 volt. On detailed spec sheets they list the gain of amplifiers as xxx dB. | |
| ▲ | RichardLake 2 days ago | parent | prev | next [-] | | That depends, the dropped unit could be either a year or a month. | | |
| ▲ | jchw 2 days ago | parent | next [-] | | You don't drop the unit for months, so it's not ambiguous in context. | |
| ▲ | klodolph 2 days ago | parent | prev [-] | | It’s understood in context, that’s the point. | | |
| ▲ | pzo 2 days ago | parent [-] | | no it's not - it's assumed by maybe taking the most likely unit (year). But if the conversation is in hospital with your kid having emergency I guess doctor would appreciate to know if they will have to do surgery on 3 months child or 3 years kid. | | |
| ▲ | observationist 2 days ago | parent | next [-] | | If the doctor has trouble figuring out the difference between 3 months and years, there are bigger problems than specificity. There are places specificity is necessary, and there are places the implicit assumptions people make are specific, and only need additional specification if the implication is violated. That's how language works - shortcuts everywhere, even with really important things, because people figure it out. There are also lots of examples of this biting people in the ass - it doesn't always work, even if most of the time, it does. | |
| ▲ | icehawk 2 days ago | parent | prev [-] | | A 3 month old kid looks very different to a 3 year old kid. | | |
| ▲ | pzo 2 days ago | parent [-] | | and thats the exact point - you assume doctor see the kid instead of you calling doctor or doctor is getting briefed by emergency stuff. | | |
| ▲ | thowawatp302 2 days ago | parent [-] | | Exactly! It makes sense in context. | | |
| ▲ | marcosdumay a day ago | parent [-] | | As long as you construct a strawmen strict enough that can be no ambiguity, and refuses to acknowledge any context where it's not enough, yeah, it always make sense in context. | | |
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| ▲ | jayd16 2 days ago | parent | prev | next [-] | | When you say 35 it would be strange for it to be anything but years. 3 days, weeks, months or years are ironically all common units when someone is "3". | | |
| ▲ | seanhunter a day ago | parent | next [-] | | No one actually says "my child is 3" meaning anything other than 3 years. They would say "3 days", "3 weeks" or "3 months" meaning the other lengths of time. | |
| ▲ | MyOutfitIsVague a day ago | parent | prev | next [-] | | Not where I live. You'd never specify how old somebody is with a bare number and have it mean anything other than years in the US. "My kid is 3" is always 3 years. So is "How old is your Tammy?" "Three". That only ever means years. Every other unit is always explicit. In my decades as a parent and being around other parents of kids and newborns, I've never experienced an exception to this. | | |
| ▲ | sanderjd a day ago | parent [-] | | That's the point. If you are talking colloquially to someone where you live, sure, whatever, this doesn't matter. But if you are writing something down in some publication for a wide and unpredictable audience, you should use units. |
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| ▲ | bigstrat2003 a day ago | parent | prev [-] | | Most of the time if someone says "he's 3", it is a good bet that they mean 3 years. People usually specify if they mean days/weeks/months with respect to someone's age. Not always, of course, but it's definitely uncommon to drop the unit when it's anything except years. |
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| ▲ | viraptor 2 days ago | parent | prev | next [-] | | That only works if you're already familiar with the context and system and assume other people are too and don't care about anyone new to that area. (Good luck coming to the audio equipment datasheet with no experience and figuring out what the dB means in each case) "He's 3" works because of the previous question and because everyone had experience of talking about age. dB for anyone not already knowing the answer is like going to another planet and hearing "he's 3". Of course it's on a logarithmic scale, offset to -5 as starting point, counting the skin shedding events - clear in context and you should've known that. | | |
| ▲ | klodolph 2 days ago | parent | next [-] | | Maybe I just live on the planet, but I don’t have this problem with dB and to me, it sounds like you’re the alien. Maybe you could elaborate, or give a motivating example? I just don’t remember encountering the problem you’re describing, and it’s unfamiliar to me. There’s something about your experience that I don’t understand, but I don’t know what it is. | | |
| ▲ | viraptor 2 days ago | parent | next [-] | | Moving from EE to audio to radio is enough to go through a few iterations of "people just write dB but mean completely different things". I got used to it, but that doesn't stop me from saying it's a bad idea and we should improve things for the next person. | | |
| ▲ | klodolph a day ago | parent | next [-] | | Audio, the only gotcha I’ve seen is that -10 is -10 dBu and +4 is +4 dBV. That one is sloppy. But this comment doesn’t illustrate your point, and I still don’t really understand where you’re seeing this. | |
| ▲ | sanderjd a day ago | parent | prev [-] | | Yeah exactly. Lots of people here can't seem to distinguish between "thing that I'm used to" and "thing that is good practice". But these are totally different. I'm used to and thus comfortable with lots of things that are nonetheless terrible! |
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| ▲ | 00N8 a day ago | parent | prev | next [-] | | I often see pop sci articles saying something like '400 dB would represent a sound strong enough to tear the world apart', or 'military sonar is X dB -- strong enough to liquefy your organs at Y distance'. It's rarely clear to me which of these usages of 'dB' are directly comparable. I think the dB measurement for sonar is a different scale/unit than the one for hearing damage thresholds in air, but I couldn't figure out how to convert between the two last time I spent a few minutes trying to look it up, so in my opinion it can be fairly confusing. | |
| ▲ | sanderjd 2 days ago | parent | prev [-] | | The explanation and motivating examples are in the article. | | |
| ▲ | klodolph a day ago | parent [-] | | The article only had bad examples in it, I was hoping for perspective from someone that made sense. The voltage / power example doesn’t make sense. It’s always power or voltage squared, which are equivalent when the load is resistive. | | |
| ▲ | sanderjd a day ago | parent [-] | | The articles examples were fine. You (and lots of others here) are being obtuse. |
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| ▲ | drob518 2 days ago | parent | prev | next [-] | | Then your complaint is with the dropping of units, not dB. | | |
| ▲ | sanderjd 2 days ago | parent | next [-] | | Yes. The point is that for some reason dB seems particularly susceptible to people dropping the units. For instance, I've heard loudness of sounds described in decibels for my whole life, and first saw the actual units people are describing when I read this article and thread today. | | |
| ▲ | drob518 2 days ago | parent [-] | | 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. Dropping units when you’re working in a particular field is quite common, as who wants to be needlessly wordy when it’s redundant and everyone in the industry understands it? IMO, this article is just the author raging about his own ignorance. | | |
| ▲ | sanderjd a day ago | parent | next [-] | | That's the whole point. You're failing to communicate clearly. You think it's fine because you're used to it. But it's bad. That you are used to and comfortable with something does not imply that it is not bad. | |
| ▲ | viraptor 2 days ago | parent | prev [-] | | 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. | | |
| ▲ | drob518 2 days ago | parent | next [-] | | 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.” | | |
| ▲ | sanderjd a day ago | parent | next [-] | | 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! | |
| ▲ | JadeNB a day ago | parent | prev [-] | | > 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? |
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| ▲ | klodolph a day ago | parent | prev [-] | | What’s to improve? I think the situation works well for people who work in the fields that use dB. | | |
| ▲ | sanderjd a day ago | parent [-] | | The improvement would be to specify the units you're working with, as is well known best practice in all science and engineering disciplines. |
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| ▲ | viraptor 2 days ago | parent | prev [-] | | Yes, that's what the whole article is about... | | |
| ▲ | drob518 2 days ago | parent [-] | | But it’s not. He’s raging against dB. | | |
| ▲ | viraptor 2 days ago | parent [-] | | 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) | | |
| ▲ | davrosthedalek a day ago | parent | next [-] | | 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 both. | | |
| ▲ | sanderjd a day ago | parent [-] | | No it doesn't. It's always bad for the actual unit to be implicit. | | |
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| ▲ | klodolph a day ago | parent | prev [-] | | 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. |
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| ▲ | formerly_proven 2 days ago | parent | prev [-] | | Can you show one of those audio equipment datasheets where it just says "<number> dB" a bunch of times and it's really unclear and confusing? |
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| ▲ | sanderjd 2 days ago | parent | prev [-] | | If you were writing a research paper or engineering artifact rather than having a casual conversation, you should specify the units ("years old") for age as well. |
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| ▲ | BobaFloutist a day ago | parent | prev | next [-] |
| I mean it's always a little bizarre when the default unit used to measure something is dimensionless. Why not set a default (like STP) that's assumed to be the baseline unless otherwise specified? It would be like if Celsius had no reference point and every time you said water boils at 100 degrees Celsius people came out of the word work to smugly correct you "Only if you first say 0 degrees C is when water freezes, which you can't assume. What if 0C is actually absolute 0?" |
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| ▲ | beloch a day ago | parent | prev | next [-] |
| 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. |
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| ▲ | sanderjd a day ago | parent [-] | | None of these other examples are contextual in the same way. |
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| ▲ | 2 days ago | parent | prev [-] |
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