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The scientific “unit” we call the decibel

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Re: The scientific “unit” we call the decibel

#11

Post by rebolek »

readthenotes1 wrote: post #4
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.

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.

Again, technically, it is. But ear isn't scientific device, neither is your amplifier. What I was describing is more than an agreement than some precise measurement. 3dB is more or less double the volume but different frequencies have different responses so I really wouldn't want to have some "perfect" way of measuring loudness as it would be so needlessly complicated that it would be useless.

Re: The scientific “unit” we call the decibel

#12

Post by timewizard »

> 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. amplitude. This is the specific reason the dB is so useful in these systems.

> the value is meaningless unless we know the base unit and the reference point

No you just need to know if you have a power or a root-power quantity. Which should generally be obvious.

https://en.wikipedia.org/wiki/Power,_root-power,_and_field_q...

Re: The scientific “unit” we call the decibel

#13

Post by timewizard »

readthenotes1 wrote: post #4
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.

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.

Human hearing perception response is logarithmic. This is part of the reason we use the unit. Our senses naturally work in that domain.

Re: The scientific “unit” we call the decibel

#14

Post by ggm »

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.…

> No you just need to know if you have a power or a root-power quantity. Which should generally be obvious.

There has to be a Yogi Berra witticism about obvious things. Suffice to say fools like me work unadvisedly in spaces where this kind of axiom isn't obvious, because we're simpletons.

Re: The scientific “unit” we call the decibel

#15

Post by ggm »

Do a deep dive into audio vu Meters and how they got calibrated. Without being 100% sure, it's basically a totally subjective model, where back in the 1920s the BBC and some US company decided to assert "like us" and two models persist which have been retconned into some BIPM acceptable ground truth but it basically was "test it against the one we made which works"

The hysteresis in the coil-magnet meter response turned out to be a feature, not a bug.

Re: The scientific “unit” we call the decibel

#16

Post by esperent »

svara wrote: post #9

A pet peeve I share! An expanded version of this article should become the article on decibels on Wikipedia. I've read that article many times over my life and for the first couple times came back thinking I was too dim to understand. Transparently leading it with "Here's something ridiculously overcomplicated that makes no sense whatsoever..." wouldn't fit Wikipedia's serious voice but actually be pedagogically very…

There's often a Criticism of... section in Wikipedia pages.

Maybe this blog post could work as a source, although it would be better to find something more established.

Re: The scientific “unit” we call the decibel

#17

Post by svara »

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.

For practical day to day use in very narrow context, yes.

But, what you're saying is only approximately correct (the factor is a bit less than 2) and there are many related fields, even in areas that would be relevant to the physics of sound reproduction, in which the same notation "dB" means something different.

Re: The scientific “unit” we call the decibel

#18

Post by formerly_proven »

Decibels make sense and it’s usually only laymen who use only „dB“. I’d be surprised if you’d find „-45 dB“ as the specification for a microphone. Here’s two random examples:

Sensitivity at 1 kHz into 1 kohm: 23 mV/Pa ≙ –32.5 dBV ± 1 dB

Sensitivity: -56 dBV/Pa (1.85 mV)

Re: The scientific “unit” we call the decibel

#19

Post by masklinn »

readthenotes1 wrote: post #4
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.

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.

3dB is “twice as loud” in that it’s twice (or half) as much power.

Part of the reason why the bel is used is that human perception is closer to logarithmic than linear (weber-fechner law), so a logarithmic scale is a better approximation of “loudness” than a linear one.

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