EEVblog #49 - Decibels (dB's) for Engineers - A Tutorial

[@mrex5769]

I'm literally 4 classes away from an electrical engineering degree and this video is the first time anyone's ever explained to me what db actually are

[@Alitar1212]

Literally same😂

[@kartikeyak3425]

13 years old but still helping so many students. I'm so glad i came across your channel!!

[@ShizzleMyChizzle]

So passionate about teaching, absolute must watch channel for any electronic engineer.

[@selvakumarr6672]

Wow, I never imagined that I will get so real meaning of dBs. Thank you so much for this. Recently i came across working with dBs in my profession, I asked many of my friends on what is the real world meaning of dBs, Frankly nobody able to explain anything closer to this. Keep up your wonderful work.

[@AlienRelics]

Are you trying to use a plural of dB by adding an "s"? That doesn't really work, I don't think there is a plural for a symbol. I was thinking you were trying to say dBspl or dBm or something like that.

[@selvakumarr6672]

@@AlienRelics . Yup that was my mistake on adding 's.

[@retrobrw919]

I'm so glad I found the EEVBlog. It's such great supplement to my college studies in Electronics Engineering Technology!

[@HamedAdefuwa]

dave, ur approach is just genius, everytime I watch your videos I get filled with "dont worry about it, its easy to understand" - all other engineering videos fill me with despair, like I've got to go back and complete 50 physics text books before I can do EE.

[@EscapeMCP]

Should have included how to work out dB's inbetween decades e.g.: 20:1 is +6dB for x2 and +20dB for x10 = +26dB 1:50 is -40db for /100 and then +6dB for *2 = -34dB Such an elegant system. You can always get pretty accurate ballpark figures without any need for calculators.

[@aerohk]

Something my professor tried to hide from me.

[@jcx5750]

+Aerohk Loooooool yes same here

[@joshuaengay1350]

Something my professor so lazy to teach thats why im here teaching myself

[@IbrahimAli-kx9kp]

Same here :D

[@coyohti]

"Because it's nicer when things get more complex." This video has not only helped me understand dB better but the above quote has helped me understand why my dad (an electrical engineer) was the way he was. 😉

[@eighthourlunch]

Excellent explanation, thank you. I wish my college professors had been as competent at distilling ideas like these into something understandable.

[@HighestRank]

Here's the straight forward equation minus the derpworthy typos and readability issues: (V.out/V.in)·Log(20)=dB.V. (P.out/P.in)Log(10)=dBm. •Inverse formula: dB.V/20=V.out. dBm/10=P.out. •Here is the -3dB. that you hear so much about: 0-3.dBx./20=0.707. 0.707Log(20)=0-3dBx.

[@2013Aleksey2013]

I'm still not quite used to describing electrical quantities in terms of decibels. The input signal has an amplitude of 500mV while the output signal is 1 Volt, so the input signal gets amplified by a factor of 2 or +6.0206dB. I was curious as to how the equation dB = 20*(log Vout/Vin) could be rearranged to solve for Vout assuming dB and Vin are known. So, dB/20 = log Vout/Vin; Vout/Vin = 10^dB/20; Vout = Vin*(10^dB/20); Vout = Vin/10^-dB/20

[@forhadahmed4643]

this man is one of the best teacher on EE on youtube. Hats off

[@fuahuahuatime5196]

Thank you for the video! I learned about dB back in school but never grasped the idea, and it's always been my biggest weakness.

[@martinda7446]

That glass is -3dB down, it had PowerAde in it.

[@HighestRank]

*---* 3dB down is 3dB up.

[@martinda7446]

Rýán Túçk Haha ok.

[@JennyEverywhere]

If someone wants to really understand logarithms, they should study how to use a slide rule. It gets the concept of logs deep into how you calculate things. There's even dedicated rules designed with radio, electronics, or engineering in mind.

[@EdMatzenik]

Here's a formula I use to mix music. 1. mix it quick and rough. 2. round everything to the nearest round figure of dBs (-7.9 becomes 8.00). Now if you accidently bump a fader, you'll know. 3. Every time you listen to the music remix it in even dB terms to the following: 1 dB up or down is the difference when a musician played note a little different, 2 dB sounds like you turned it up or down a little bit, + or -3 db is a lot. Any more than 3... must have been ridiculous to start with.

[@kevinchau5336]

I'm about to graduate from college with an EE degree, I've learned more from your channel than the UofA has taught me.

[@BariumCobaltNitrog3n]

You just weren't paying attention. Also you can't pause and replay a college prof thousands of times.

[@salat]

@shodanxx: I'm a ham too and I it's easy to rembember: If you double the voltage in a circuit,the current doubles too and since P=I*U we get: 3 db(V) which leads to a an increase of 3db(W) e.g. with a 1 Ohm circuit: from 1V to 2Volts there's a ~6db(V) gain from 1W (1V * (1V/1Ohm)) to 4Watts (2V * (2V/1 Ohm)) we get 6b(W) gain that's the reason for 10*log(p1/p2) for power and 20*log(v1/v2) for voltage.. 73, DO9SAS

[@abberdakas6294]

Thanks Dave!! Some subjects in class leave me more confused than i was when I started, so I come home and watch your videos and it all becomes clear. Excellent video

[@garypoplin4599]

20:25 - For years, I’ve had the same answer to the “Is the glass half full or half empty?” rubbish: there’s not enough information to answer the question. The correct answer is “It depends!” Now had you started with a full glass and drank half of it before this shot, I would agree. However, if you started with an empty glass from the cupboard (which is more likely what happened here) and filled it it half way just for this shot, as an engineer, I would have to say it’s +6dB. btw, this video is the most concise explanation of dBs I’ve seen!

[@1SmokedTurkey1]

Better than my Communication Theory prof's explanation, which took more than 2 classes and I still didn't get it. Thanks!

[@patrickwall144]

Thanks. all I was looking for was what was being measured in respect dBm. After the last guys video what I had was 10log10 something over .001 = Powerin over Power out and he finally just gives the 6dB 20dB 30dB says thats what it works out to and informs you you understand dBM. I started out knowing the majority of it. found myself a little cobfused and simply wanted to know what I was measuring. I ended up knowing less than I did when I started. You answer the question in the first min. then bring some sanity and structure back to my thinking with the rest. Thank you.

[@PileOfEmptyTapes]

Since it seems to be a common question: dBs in sound are easy. dB SPL (sound pressure level) is dB relative to 20 µPa, a value close to the mid-frequency human hearing threshold. (It's AC, so probably an RMS value.) Now sound pressure is analogous to voltage, and sound particle velocity relates to current in the same way. Hence, it's "voltage dBs". A microphone will usually have a spec'd sensitivity in dBV / 1 Pa = dBV / 94 dB SPL. This directly links the sonic to the electrical side.

[@AndresMilioto]

I'm on the 4th year of engineering school (here on argentina the career is 5 years long), and I have to say you are totally ruining my education, because now all my teachers seem REALLY boring. THANK YOU!! YOUR BLOG IS THE BEST, I CAN'T GET ENOUGH OF THIS VIDEOS!!!

[@scottpelletier1370]

What are you working on now?

[@AndresMilioto]

@@scottpelletier1370 I ended up getting a PhD in Robotics. It was a wild 9 years lol

[@scottpelletier1370]

@@AndresMilioto haha that's awesome! Congrats and thanks for the quick reply.

[@RW1701]

This guy is so enthusiastic!! How can you not get excited about electronics listening to that voice!! This has really tickled me haha

[@sbrscoading801]

no one told me why to use DB in Bode Plot.... it's you sir who made me understand.. thanq

[@ri438j]

I was introduced to db's (analyzing filters) in my electronics class last semester, but now I have a much better understanding thanks to you Dave! Great Job!

[@hoofbags]

For some reason, as with quite a few amateur electronics hobbyists, I had a blind spot for dB. As usual, your explanation is hugely helpful. Many thanks. (o:

[@italicus84]

Remember that also dBi uses the 10* Log formula. dBi is a value for antenna gain. The gain is the power radiated per solid angle / power received from the transmitter per solid angle. When the ratio is 1, we have an isotropic radiator (which is ideal). Since it's a ratio between powers, the 10* Log formula shall be used.

[@dylan_king1870]

this was such a great explanation and your excitement made it really enjoyable. thanks.

[@oobihdahboobeeboppah]

Great tutorial on decibels for anyone getting started in technology; highly recommend this video for anyone studying for their Technician Amateur Radio license.

[@josediaz85]

Another engineering example: it is common practice to use Decibel scale to represent harmonics signals, for example in power quality when representing the fundamental voltage together with the harmonic content of a signal, normally the fundamental is much much bigger. Thank you Dave for your videos!!!

[@tushar8133]

9:11 - "It's less than the width of the one fibre on the tip of this pen" This shows the perspective of how an experienced person visualize 😊

[@rockydogsdad]

Have used dBohms before. Since I=E/R, then in log format, dBuA=dBuV-dBohms. Used to calculate current when measuring voltage with a current probe - probe cana correction factor vs. frequenct in dBohms! Nice and easy.

[@rockydogsdad]

Sorry about the typos. The current probe has a correction factor in dBOhms.

[@Daniel-p3g8q]

Episode 49! My how far you have come. Watched you for close to a decade now.

[@87knox]

Decibels were originally designed for power, so the formula for power is 10*log(a/b). However, power is proportional to the square of voltage. Therefore, if you double the voltage, the power will quadruple. Based on the algebraic rules for logarithms, if you take that power of two out of the argument, it will multiply the result. 10x2=20, so the formula for voltage is 20log(a/b).

[@kchididdy]

Correct me if I'm wrong Dave.... I generally don't like to memorize formulas. I would probably go one step further and state that power is proportional to the square of magnitude. In high school math, we learned that (assume log base 10): log (v^2) = 2 log(v). Since we are dealing with "deci" Bels, we multiply both sides by 10 to yield: 10 log (v^2) = 20 log (v). In other words, dB values are indeed ratios, but it's implied that the ratio is in terms of power/intensity.

[@zanfr123]

Thanks to this I finally understand (at my age lol) how dBs work and how they can come in handy.

[@2ndlars]

When you're talking percieved volume you're talking psycho acoustics. Twice the amplitude of sound will not sound twice as loud. That's (if I remember correctly) because it's not twice as far above your hearing threshold. AND it only holds true for what's called "normal hearing" because people with a hearing loss will have a smaller range of hearing.

[@ForViewingOnly]

Great video, very clearly explained. I've only watched 3 of these blog vids and I'm hooked! Dave's enthusiasm is infectious!

[@diogenes9991]

It's easy to get the idea, but I love the way him explaining. Congratulations and Electronics for all!!!!!!!!

[@andymouse]

13 years and still cool and relevant....cheers.

[@Richard_Broom_Photography]

An excellent video. Swept away years of misunderstanding.

[@teddyr101]

"-6dbr", the industry standard for half a rabbit?

[@CairosNaobum]

is "rabbit" a power or a magnitude ?

[@electra]

Great videos. Please continue to do these traditional electrical engineering topics/issues and ignore the people that request simpleton versions or projects and hacks. There's plenty of that junk on the internet already.

[@srira7910]

Wow, this was really helpful, great perspective. Gifted teacher.

[@marshallnmoonshine]

My great great great great great great (plus however many more) grandfather invented logarithms. Dig your channel, man! Thanks!

[@PileOfEmptyTapes]

Now if you want something *hairy*, try calculating the voltage and power gain of a unity gain buffer (with an actual source and load). Hint: You can express both in dB, but the value will not be the same. Why?

[@stevetobias4890]

Thanks Dave, loved the explanation. Helped heaps mate! 👨‍🎓 I can't go by rule of thumb, half of it is amputated, lol

[@ericjw7]

Thanks for all your videos, I've gotten something out of all of them

[@hynekboruvka8346]

Nicely explained, thanks a lot! Longer than other useless explanation videos, but short enough to be able to stay focused whole way.

[@JimmyTheShell]

This is just brilliant! You have a gift explaining things!!

[@xoox870]

The reason why voltage is 20 times the ratio compared to power which is 10 times the ratio; is because the derivative of V^2 (used to calculate power) is 2*V - - - there is significant confusion with dB, dBm, dBw, dBi, dBd, and others if you don't know the 'context of the application', especially with voltages or powers. 6dB is double for voltage , but 3dB is double for power !! it is better to use dBW or dBmW for watts and dBV or dBmV for volts to avoid confusion. - - - decades are relative to 10's of dBs not scales as mentioned. - - - negative decibels are simply the reciprocal of positive decibels. @ 19:45 he has it backwards !! - volts are a power since they are squared and watts are a magnitude since they are NOT squared. this is why for volts there is 20X the log since V^2 is used in power formulas. - - - FYI 555 timers are one of the worst crappy electronic parts there ever invented. - please research monostable multivibrators for much better parts ; at least they can produce a 50 % waveform; a 555 cannot since at 50% both comparators would trigger !!

[@pvbinoyable]

@yeoldeengineer the value will be same. for calculating power in decibel you have to use 10 log (P2/P1) and for voltage 20log(V2/V1) . you might have used same formula for both. thank you

[@ddemon4406]

very helpful video. felt like you were going to poke my eye out with that marker.

[@aceboogiebooyah4278]

I hope this guy comes knocking on my door one day as a dB salesman, and I can thank him greatly for selling me on dB's long ago, and to sign me up for more! HaHA You rock guy! Power to the people!!! (dB's)

[@LuisFZ]

Your channel is awesome. there are few like you in the internet, and when I say "like you" I mean trustable people when it comes to scientific debate

[@simonndungu1196]

This guy has great sense of humour, nice explanation

[@rehmanzed]

this channel deserve million subscribers ...

[@bennyattar8862]

No one has ever explained this more clearly.

[@KostadinIVKostadinov]

Water is closer related to power than voltage. Filling with water requires potential energy, which can be achieved by power (voltage and current over time). According to that, your glass is (approximately) only 3dB down! (discuss)

[@markfinkbeiner3034]

Thank you. What a practical use of the log scale.

[@markuscwatson]

Aaaaaaaaaaahhhhhh.... using the dB scale on a FT allows you to view small and large signals on the same scale: good for seeing the noise floor. I always set the scale to Linear because it’s easier to understand. Now I will keep this video in mind.

[@bp968]

Interesting. I've always thought of dB's as a measurement of sound level. It's interesting in the gun world to see how confused people get when talking about dB sound levels. People see the sound level of a silenced/suppressed gunshot (136-138dB for a 5.56mm) and say "well that's not quiet, that's as loud as a jet engine!". Which is only partially true. The gunshot is an impulse sound and an extremely short one (microseconds I believe) while the jet or jackhammer is continuous. Once you see how the human ear "hears" you quickly grasp that the 136dB is actually pretty quiet. Especially when compared to the original sound level of 160-168dB!

[@krish2nasa]

Excellent explanation, Thanks Dave

[@PileOfEmptyTapes]

Oh, and: Nice tutorial, Dave! I'm not sure I could explain it that well, dBs have been with me since my teens. The problem below still had me scratching my head though. It's amazing how these supposedly basic things can still trip you up at times.

[@dannyleefye]

According to my Spectrum Analyzer it looks like you have a 50 Hz hum in your audio. When it is not obscured, I also see a signal at 100 Hz which is usually a bit stronger. So maybe you have a ground loop problem? I am not trying to be goofy or anything like that, I just wanted to let you know. Thanks much for the GREAT videos! P.S. I am in 60 Hz land, so I know it is not on my end.

[@WizzRacing]

Its funny how optical lenses work on the same principle. I think they called it rule of halves in photography class. One stop down is half, one stop up is twice as much.

[@jpmcbride]

The 20log and 10log formulas really confuse people. Its easy to explain though ... First, the dB is defined in terms of power as dB = 10 log (P1/P2) If you want to solve for voltage, you substitute into the above formula P=V^2/R to get, dB = 10 log [(V1^2/R) / (V2^2/R)] Now cancelling the R's above gives us, dB = 10 log (V1/V2)^2, And the rules of logarithms let us move the 2 down like this, dB = (2) 10 log (V1/V2) which gives us our dB formula for voltage, dB = 20 log (V1/V2)

[@vk3hau]

And don't forget dBi " decibel over isotropic Antenna"

[@mikedemoore6670]

Great Dave!!! Perhaps there would be more engineers around if we were taught by people like you?

[@yogishgajadur2513]

Perfect for measuring my stress level during exams

[@fardellp]

What an outstanding tutorial. I would say that Dave is unique in his ability to explain electronics. My only concern is for his health. He is so passionate about explaining concepts (especially BS) that I fear he might be heading for a stroke.

[@zilym]

Nice lecture. Makes sense. Hopefully I'll remember it next time I run into dB's.

[@stokes111111]

awesome video and I love your energy, thanks for this!

[@RecordingStudio9]

Wish I had you as my electronics teacher some 30 years ago! I would have lived at TAFE!

[@V109FM]

Thank you, very well done video and helped me understand it much better.

[@DianneStudio]

Very nice informative video!! Cant digest!! lolz! how to calculate the fan's sound! that's y I am here! I am like doped .. lolz!! DB in audibility ... thank you

[@josenieves5038]

Question -- Can you do a comparison of SPL meters like you did on the multimeters? Is a cheap meter reliable enough to an expensive meter? Certification standards? I've watched a few of your videos and always learn something. I really loved your Multimeter shootout and actually didn't watch it until after I purchased a Klein MM700 and CL700. I realized a year or so later I really wanted the CL800 for DC current (I had overlooked that difference) which I got and would have purchased originally if I watch your shootout.

[@LynkedVideos]

Why should we care about the "ancient" unit of Bel? In 1920, Bell Telephone created the Bel to represent the base10 log of a power ratio. The name of the new standard for measurement was a dedication to Alexander Graham Bell. Decibel was the recommended unit. Since the decibel is an exponential unit of power measurement, its use with potential is a derivation. Assuming that a change in potential results in a linear current response, then we can derive a measurement in decibels to describe the voltage change in this ideal system; however, the measurement still defines a power ratio. Thus, I suggest that we should care about the Bel and its creation. In regard to your glass of milk, I will assume that the vessel is a perfect cylinder. You now have more power than you need, because with only half the columnar height (potential), you will consume fluid at half of the rate (current) as full. Next time I suggest buying proper conical glassware so that you can supply power at a rate that is commensurate with its remaining potential. Do you like martinis? ;oP Party on, Dave!

[@HighestRank]

Use a straw.

[@Jamesrevelations]

Thanks a tone dave,,,,awesome information...i wonder if you can put up a lil more on the use of DB in sound ...loved it all,,,,God bless keep it coming

[@sonicelectronic7990]

Been "using" dBs for decades and never really understood. Now I get it! Thanks! P.S. I've always said the glass is both half full AND half empty, what does that make me?

[@VilleWitt]

Bipolar?

[@MrMexUniversal]

Hey brother, thanks for your passion and your time.

[@sidpryce]

best dB explanation on the Internet

[@garynorthtruro]

Thanks, this does make it a little better understood.

[@selinamutalimanja3660]

cool stuff learnt a lot,had problems with Dbs merci beaucoup

[@pgadams1]

Love it. So easy to learn this way.

[@tejeshwvardhan1165]

believe me if i ask my teacher "what is dB". in return i would get "very good question????????????"

[@khadijaqayyum8360]

haha.. ideed a very good question

[@dug86f]

This guy is the king!

[@pearsgr]

thanks can you add some details about decibels readings on a multimeter please

[@drdave1947]

We need an engineer to invent a decibel-controlled TV so that programs don't try to damage my hearing with loudness, AND so I can hear the soft sounds. About 7.0 would be great, but it needs to be adjustable.

[@mohammedfaizan6197]

Started loving db's

[@unitedelectrician4334]

Great Video clear my abstract thinking

[@sherifnegm9046]

thanks so much. Your tutorials are very useful to high school physics students too xD

[@fuahuahuatime5196]

Lol. Doubt you'd learn this in high school physics. You don't even learn it in college physics.

[@johnmanzang7272]

Thank you very much for a very good explanation!

[@Interdiffusion]

Brilliant presentation, really useful stuff!!!

[@abuzarramli2510]

I'm really loving the explanation. thank you mister. also enjoyed it as well :)

[@BigNate84]

I have a question pertaining to the 19:08 minute mark of the video. How come -3 dBm is = to 0.5 mW? Above that I am seeing -6 dBv also = to 0.5 v. Is this because orders of magnitudes use 20 Log and power uses 10 Log? Or is this an error in the white board math? The video covered the rules of thumb for magnitude which makes sense to me, I'm just wondering what the rules of thumb for power are if they are different? Thanks!

[@BigNate84]

I guess I was expecting -3 dBm to be = to 0.707 mW based on the rules of thumb you described in the video.

[@cbbuntz]

I'm replying 5 months after your comment. Anyway, my understanding is that power is expressed as 10*log10(x) while voltage or current is 20*log10(x) because watts = volts * amps. So 2 v * 2 A = 4 W or 0.5 v * 0.5 A = 0.25 W If both volts and amps increase / decrease by the same proportion, it's equivalent to the squared difference in power and dBv and dBm will change by the same amount. Multiplying a logarithm by 2 is the same as squaring 10*log(x*x) = 10*log(x^2) = 20*log(x) Therefore -3 dBm is 0.5 mW and -6 dBv is 0.5 v

[@tomcass240]

So if I buy an antenna and it says 3db gain, what is the "reference value" in that example?

[@garryjones2482]

Brilliant and enlightening.