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I understand what a decibel is, the spirit of the question is different: why do we still use decibels (and with at least two different, context-specific definitions), if we have the feat of scientific notation? I dare to claim that the change of 5e-1 (which is a half) is much more readable than 3dB (voltage? power?). 1e6 is more clear than 120dB, etc. Just for the joy of adding? 3dB + 7dB is 10dB, but 2e5+3e6 is errrm... I see many new datasheets from the top vendors (LTC, for example) use the V/V convention, which is closer to the scientific notation than to the decibels. An upcoming paradigm change?

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    \$\begingroup\$ Is that 5e-1 voltage or 5e-1 power? Why is 5e-1 more readable than 0.5? \$\endgroup\$ Commented Jan 31, 2018 at 23:38
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    \$\begingroup\$ Uhmmm, why are we still using Roman numerals? \$\endgroup\$
    – Transistor
    Commented Jan 31, 2018 at 23:40
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    \$\begingroup\$ Because it's the twenty-oneth century apparently. \$\endgroup\$
    – Ian Bland
    Commented Jan 31, 2018 at 23:41
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    \$\begingroup\$ What's wrong with saying: "I went on a date with a girl -3dB of my age." \$\endgroup\$ Commented Jan 31, 2018 at 23:48
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    \$\begingroup\$ dB or not dB? That is the question? (With a nod to WS.) \$\endgroup\$
    – Transistor
    Commented Feb 1, 2018 at 0:09

3 Answers 3

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You use dB because you can add together logarithmic numbers which is much easier than carrying around scientific notation. It also lets you compare numbers regardless of scale.

\$50dB+1dB=51dB\$
is easy to do in your head

\$3.1622e2*1.122e0\$
not so easy to do in your head because you have to find which part of the scale your on.

With graphing it also becomes very handy because it lets you know that the scale is logarithmic. If we threw away dB we would be restricted to using the chart above instead of the chart below. The linear chart loses meaning in the upper frequencies range because the larger frequencies swamp them out. In the plot below, we can see there is a second pole in the system that could not be seen below. enter image description here

I fully support dB units.

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    \$\begingroup\$ Your second equation should have a multiplication sign instead of a plus sign if you want to compare it to decibels summing. Then advantage of decibels is even clearer. \$\endgroup\$ Commented Feb 1, 2018 at 5:55
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No offense Peter, but your question seems a bit absurd. Decibels do express a good way to judge sound level and noise ratios, but an op-amp datasheet also has ppm for drifts and V/V for gain, and the roll-off point for frequency response is -3 dB at frequency 'f'.

Roman numerals are not normally on data sheets but are good for dating movies that may be shown in many countries, some who still use roman numerals. I understand them very well.

The point is that we use whatever codex/radix or descriptive scheme works best for a given set of numbers. Some refer to absolute values while others are ratios. Why is hexadecimal and binary still used in programming when we have such advanced languages to use?

EDIT: I noticed the OP cleaned up his question to delete remarks about Roman numerals, and mostly wanted an answer about decibels and why they are used so much...sigh.

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  • \$\begingroup\$ No offence taken, a good remark with the ppm, which is multiplicative in nature and, being a ratio from the very beginning, fully deserves to be decibelized. But we don't do it, a ppm/1e-6 is considered to be better. Just an internalized convention or something deeper? The additivity of logarithms is a huge benefit, indeed. \$\endgroup\$
    – peter
    Commented Feb 1, 2018 at 0:11
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LTC uses V/mV for linear gain which changes alot at low voltage and is load dependent. So does max output swing.

So many others such as scattering parameters, PSSR, CMRR are still done in dB.

To assume all ratios should be expressed in dB is progress may be incomplete logic as in 1+1=0 when we all know 0 dB = 1 for gain.

' as you were'
carry on....

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