The scientific “unit” we call the decibel • Hacker News Board

Re: The scientific “unit” we call the decibel

#341

Post by monster_truck » Thu, May 22, 2025, 3:01 PM UTC

strbean wrote: post #333

drob518 wrote: post #324

Earlier quoted context omitted.

But obviously we don’t. So, there’s your counter proof.

Except the various disasters caused by assuming the wrong units (Mars Climate Orbiter, for example).

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

Re: The scientific “unit” we call the decibel

#342

Post by davrosthedalek » Thu, May 22, 2025, 3:03 PM UTC

colejohnson66 wrote: post #237

HPsquared wrote: post #220

It's a bit like "percent". A shorthand for dealing with ratios, often with hidden assumptions.

Sure, but you never say "the production is at 50%". 50% of what ? Peak possible output? Typical output? That's what the author's complaint is: dB, while arguably useful, is annoying because people leave out the part that it's relative to . And then people, when talking about dB, assume the other party has knowledge of what their ratio is relative to. dBm, dbSPL, etc.

In every communication, the sender assumes that the other party has some knowledge. For example, I assume that you can read my badly worded English text. There is rarely confusion with the people in the fields that use dB a lot. That other people often get confused by dB is not a failure of dB, not even of its common use, the same way I can't blame English for not being Chinese, or for Americans use F instead of C, or K, for temperatures.

Re: The scientific “unit” we call the decibel

#343

Post by drob518 » Thu, May 22, 2025, 3:05 PM UTC

viraptor wrote: post #340

drob518 wrote: post #323

Earlier quoted context omitted.

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. Droppin…

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.”

Re: The scientific “unit” we call the decibel

#344

Post by davrosthedalek » Thu, May 22, 2025, 3:06 PM UTC

rocqua wrote: post #63

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.

That's great, but only if 'Base level' is clear to everyone involved. Besides the base level, you also need to define what exactly you are measuring. Including the frequency weighting. This makes a spec sheet that says "this machine produces X dB of sound" effectively useless.

Any reasonable spec sheet would not say that. I say reasonable, because in the audio world, people pay extra money for oxygen-free copper cables.

Re: The scientific “unit” we call the decibel

#345

Post by MegaDeKay » Thu, May 22, 2025, 3:07 PM UTC

holowoodman wrote: post #56

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…

Decibels are completely ridiculous. They are only useful if you are a cable monkey just adding and subtracting amplification/dampening factors. As soon as you need to do any kind of non-trivial conversion or computation, dB* is more of a hindrance to understanding and simplicity, because you will always need to look up in some strange table of dB weirdness. Integrate over a spectral power density in dB/Hz? You better…

I'd say the engineers I knew building satellites at companies like SS/L and Boeing deserved a better title than than "cable monkeys".

Re: The scientific “unit” we call the decibel

#346

Post by davrosthedalek » Thu, May 22, 2025, 3:08 PM UTC

relaxing wrote: post #174

readthenotes1 wrote: post #4

Earlier quoted context omitted.

So on my amplifier, 0db is the loudest and -50db, where I usually listen is what? -47db is definitely not twice as loud as -50db, of course.

You should have a legitimate question as to what dB’s the amp is referring to. What brand and model is it? First, is it actually specified as dB’s? Most amps I’ve seen display volume on an arbitrary scale, no units specified. Second, the amp has no way to know dB sound pressure, as that depends on the rest of signal chain. So is the displayed figure referring to dBu, dB mV, something else, or something totally bunk?

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.

Re: The scientific “unit” we call the decibel

#347

Post by detourdog » Thu, May 22, 2025, 3:08 PM UTC

GuB-42 wrote: post #259

rusk wrote: post #218

Earlier quoted context omitted.

You are bounded by a minimum floor for the hot water. Below a certain point you can get legionnaires. To me it seems like one of two things: external pressure between hot and cold is mismatched so a small change to one side overwhelms the weaker flow. Alternatively it might just be a broken or poor quality mixer that isn’t providing the appropriate ‘nuance’ of control, and that may indeed be expressed as some sort of…

> Below a certain point you can get legionnaires. I know you mean legionnaires' disease, but the idea of a bunch of soldiers getting to your house because you turned your boiler too low made me chuckle. Good thing the US have the third amendment to protect against this.

In this day and age I believe anything is possible.

Re: The scientific “unit” we call the decibel

#348

Post by nyeah » Thu, May 22, 2025, 3:10 PM UTC

viraptor wrote: post #312

nyeah wrote: post #260

Earlier quoted context omitted.

Right. Decibels are my idea.

Projecting in that context means you claimed what other people think/do, because it's what you think/do. It's about describing the conscious choices of others (where my experience disagrees for example) not about decibels specifically.

Agreed, you are using the word "projecting" fine. But you're ignoring the actual behavior of people using dB in the real world.

Re: The scientific “unit” we call the decibel

#349

Post by drob518 » Thu, May 22, 2025, 3:10 PM UTC

strbean wrote: post #333

drob518 wrote: post #324

Earlier quoted context omitted.

But obviously we don’t. So, there’s your counter proof.

Except the various disasters caused by assuming the wrong units (Mars Climate Orbiter, for example).

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.

Re: The scientific “unit” we call the decibel

#350

Post by davrosthedalek » Thu, May 22, 2025, 3:12 PM UTC

hashhar wrote: post #103

coldtea wrote: post #50

Earlier quoted context omitted.

> Human hearing perception response is logarithmic. It is, but -50db to -47db (+3db) is not double perceived loudness. It's double power. About +6 or even +10db would be double perceived loudness.

Going from -50dB to -44dB is a much louder change than going from -6dB to 0dB. Human hearing is logarithmic. The dB is measuring ratio of sound pressure level and it's accurate that +/-3dB is almost doubling/halving of the SPL.

That doesn't make sense. -50dB to -44dB and -6dB to 0dB is the same change in power, as a factor. If human hearing is logarithmic, the same factor produces the same increase in loudness.