Post by thread:[OT]: How to read dB?

Hi! What is dB? what is the relativeship of value in dB with voltage (caculation formula)? If for volume, 20dB, 0dB,-10dB and -50dB which is bigger? Coz I am totally blind in reading value in dB.... T.Q. regards, William -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

> >If for volume, 20dB, 0dB,-10dB and -50dB which is bigger? Coz I am >totally blind in >reading value in dB.... Decibels (literally, 10ths of a Bell) are relative power units. You can only correlate them to voltage if you already know the impedance. A gain or loss of 3dB is half or twice power When you express power in dB, you must give it as dB relative to something. 3dB is literally saying "twice as much power" If you want to say an absolute amount of power in dB, you relate it like dBm (dB milliwatt) or dBW (dB watt) -50dB is MUCH smaller than +10dB. In fact, it's 60dB down from 10dB, or 1/1000000th the power. 30dB is a factor of 1000. My audiologist once told me that at a specific freq, I had a "minor" hearing loss of 60dB. I asked her how she'd like a "minor" paycut of 60dB. She'd be making about $0.10 that year. I got a new audiologist now. :) -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to FINDU here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

dB has no units. dB is a relationship between two values. Speaking of voltage: dB=10*log(V1/V2)=10*(logV1-logV2) for example, if you want to know the gain in dB for an amplifier you take Vin and Vout and apply the formula: Vin=0.5v Vout=10v 10*log(Vout/Vin)=10*log(10/0.5)=13dB 0dB is when the relationship between the two numbers is 1, for example: 10*log(1/1)=0dB Another way of seeing this relationship is as 'gain' or 'loss'. When you have a negative value in dB it means that the relationship between the numbers is less than 1, for example: 10*log(1/5)= -7dB (aprox) One common reference used when dealing with power is 1 mW, so if you have 1mW of power out of something compared to the reference you have 0dB. But if you have, for example, an amplifier that gives out 100W of output for each mW of input, you then have an amplifier with a gain of: 10*log(100/0.001)=50dB Bye Calvin {Original Message removed}

Hi, ----- Original Message ----- From: David VanHorn <spam_OUTdvanhornTakeThisOuTCEDAR.NET> | > | >If for volume, 20dB, 0dB,-10dB and -50dB which is bigger? Coz I am | >totally blind in | >reading value in dB.... | | Decibels (literally, 10ths of a Bell) are relative power units. | You can only correlate them to voltage if you already know the impedance. It's a little bit of math. Relative power, in dB: 10*log(Po/Pi). OK, but since P=(V^2)/Z, the voltage *gain* in dB is directly: 20*log(Vo/Vi), taking the same reference impedances. For voltage expressed directly in dB, ussually (if no otherwise specified) it's implicitly considered a 600 Ohms impedance (from telephone lines...). | 30dB is a factor of 1000. That's for power relations. For voltage relations, 30 dB is a factor of aprox 31.6 (between Vo & Vi: Vo/Vi) . Best Regards, S.- -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam@spam@mitvma.mit.edu with SET PICList DIGEST in the body

> >That's for power relations. For voltage relations, 30 dB is a factor of >aprox 31.6 (between Vo & Vi: Vo/Vi) . Right, but as I said, you can't get an absolute voltage without a reference, and an impedance. You can get the ratio of Vo/Vi, but not the absolute. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to FINDU here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email listservKILLspammitvma.mit.edu with SET PICList DIGEST in the body

You do not require resistance to define an "absolute"voltage. ie. dbV = 20 log (V2/Vref). You can define the standard you are referring to. eg. dBuV = 20 log (V2(uV)/ 1uV) You may need resistance for POWER measurements if you want to state it in terms of Voltage or current ratio. ie. dbW = 10 log (P2/P1) = 10 log ((V2^2/R2) / ((Vref^2/Rref)) Regards David Huisman -- http://www.piclist.com#nomail Going offline? Don't AutoReply us! email .....listservKILLspam.....mitvma.mit.edu with SET PICList DIGEST in the body

I know this is an old post but I had some time to think about it. ----- Original Message ----- From: David VanHorn <EraseMEdvanhornspam_OUTTakeThisOuTCEDAR.NET> {Quote hidden}> -50dB is MUCH smaller than +10dB. In fact, it's 60dB down from 10dB, or > 1/1000000th the power. > > 30dB is a factor of 1000. > > My audiologist once told me that at a specific freq, I had a "minor" > hearing loss of 60dB. > I asked her how she'd like a "minor" paycut of 60dB. She'd be making about > $0.10 that year. > > I got a new audiologist now. Did she tell you how to do your work? Why should you tell her how to do her work? That was not something worth switching professionals. Auditory perception works on a different scale, AND she's saying relatively speaking, compared to people that have it much worse and still manage to live life hearing. Generally 10x real power means only about 2x percieved loudness difference. So your 60dB difference would be 2^6 ~= 1/64th the percieved power. It's still a big drop but it's actually quite workable. Jeff -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

> > > I got a new audiologist now. > >Did she tell you how to do your work? Why should you tell her how to do her >work? Because she's working for me. My new audiologist agrees too. > That was not something worth switching professionals. Auditory >perception works on a different scale, AND she's saying relatively speaking, >compared to people that have it much worse and still manage to live life >hearing. I thought she wasn't paying adequate attention to my condition. I went elsewhere. You have a problem with that? >Generally 10x real power means only about 2x percieved loudness difference. >So your 60dB difference would be 2^6 ~= 1/64th the percieved power. It's >still a big drop but it's actually quite workable. You try it. -- Dave's Engineering Page: http://www.dvanhorn.org I would have a link to FINDU here in my signature line, but due to the inability of sysadmins at TELOCITY to differentiate a signature line from the text of an email, I am forbidden to have it. -- http://www.piclist.com hint: The list server can filter out subtopics (like ads or off topics) for you. See http://www.piclist.com/#topics

At 08:32 PM 6/2/01 -0400, Jeff DeMaagd wrote: >Generally 10x real power means only about 2x percieved loudness difference. >So your 60dB difference would be 2^6 ~= 1/64th the percieved power. It's >still a big drop but it's actually quite workable. Sorry - not right! 60 dB is a voltage ratio of 1000 to 1. Lets put it this way: the hiss level on your car cassette deck is about 45 dB below peak level. 60 dB is 15 dB quieter than that. A good quality studio grade open reel tape deck (Ampex, Studer) is about 60 dB dynamic range. The best I've ever seen in a cassette deck is about 50 dB. Note: all of these tape noise figures are with NO noise reduction (which is how you align tape decks). So, yes, a hearing loss of 60 dB is QUITE something to be worried about! dwayne Dwayne Reid <dwaynerspam_OUTplanet.eon.net> Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 17 years of Engineering Innovation (1984 - 2001) * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.

----- Original Message ----- From: David VanHorn <@spam@dvanhornKILLspamCEDAR.NET> > > > I got a new audiologist now. > > > >Did she tell you how to do your work? Why should you tell her how to do her > >work? > > Because she's working for me. > My new audiologist agrees too. OK then. > I thought she wasn't paying adequate attention to my condition. > I went elsewhere. You have a problem with that? So the audiologist putting things in relative perspective made the situation such that you weren't recieving proper care? I guess I don't know enough specifics. > >Generally 10x real power means only about 2x percieved loudness difference. > >So your 60dB difference would be 2^6 ~= 1/64th the percieved power. It's > >still a big drop but it's actually quite workable. > > You try it. Actually I have all my life, I have hearing aids. Human hearing simply does not scale directly to electrical engineering and they are both analyzed from different perspectives. Jeff -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.