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.
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.
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.
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.
"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. 😉
@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
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
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:
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.
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!
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!!!
Great tutorial on decibels for anyone getting started in technology; highly recommend this video for anyone studying for their Technician Amateur Radio license.
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.
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.
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
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.
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.
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!!!
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.
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.
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.
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.
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)
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.
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.
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.
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.
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!
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).
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
@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
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.
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!
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
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)
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?
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 !!
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!
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?
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.
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.
