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Natural Science Forum / Physics / Acoustics / September 2006loudness and dBs
Hi, I think I'm right in saying that a 16-bit audio CD has a max amplitude of around 93dBs. If I play a sine wave a this amplitude, then suddenly drop its amplitude to 83dBs, am I right in saying that the result is a sine wave that sounds half as loud as the first dine wave. Thanks, Aine. First the sound level your hear from of your loudspeakers is dependent on their capablity, the power provided, the distance you are from them, the environment you are in and probably some other factors including where you have controls set. What is recorded on the CD just influences how that sound changes. The CD has no control on the absolute level. The 93 dB you are referring to is probably the dynamic range or signal to noise capabiltiy of the CD, that is the difference between the noise floor of the CD where you hear hiss and the loudest sound possible on the CD. Now, if you play a 1000 Hz tone at a measured level of 93 dB and then decrease the level by 10 dB, it would sound approximately half as loud. The actual amount of sound would be 10% of the original. That is, if you want to make something sound half as loud, you have to eliminate 90% of the sound, or if you want it to sound twice as loud, you need 10 times as much sound. > Hi, > [quoted text clipped - 6 lines] > > Aine. > Now, if you play a 1000 Hz tone at a measured level of 93 dB and then > decrease the level by 10 dB, it would sound approximately half as > loud. The actual amount of sound would be 10% of the original. That > is, if you want to make something sound half as loud, you have to > eliminate 90% of the sound, or if you want it to sound twice as loud, > you need 10 times as much sound. It is difficult with psycho acoustics. Ask a musician with a fiddle to play a melody. Then ask him to play double as loud and then half as loud. He will not unterstand you. Because there is not such an exact thing as double the loudness. You can only make a guess. Ask someone who drinks a cup of hot coffee to add cool water that it tastes half as hot. What is half as hot and compare it to half as loud. Not easy! Now tell the world that it is "10 dB" difference :-) Cheers Jens > It is difficult with psycho acoustics. Ask a musician with a fiddle to > play a melody. > Then ask him to play double as loud and then half as loud. He will not > unterstand pp, p, -, f, ff? How about 3 dB (acoustical noise "JND") per such step? I count four commas, so there must be at least a 12 dB range... Or do we use the astronmical 'magnitude' step (4 dB), whence 16 dB. Anyone? Angelo Campanella >> It is difficult with psycho acoustics. Ask a musician with a fiddle >> to play a melody. >> Then ask him to play double as loud and then half as loud. He >> will not unterstand > pp, p, -, f, ff? > How about 3 dB (acoustical noise "JND") per such step? > I count four commas, so there must be at least a 12 dB range... > Or do we use the astronmical 'magnitude' step (4 dB), whence 16 dB. p is louder than pp, f is louder than p, but there is no fixed step in between. There is no yardstick given by musicians. Only psycho-acousticians are telling us, that they are shure what doubling really is: It's about 10 dBs. Cheers Jens >>> It is difficult with psycho acoustics. Ask a musician with a fiddle >>> to play a melody. [quoted text clipped - 12 lines] > >Cheers Jens It all depends on the question you ask. Play two sounds and ask "How much louder than B is A?" and you will get blank looks. If, on the other hand you ask "Is A twice as loud as B?", there will be a range of variation over which many people will say yes. That will average somewhere around 10dB for a western population. I suspect this to be a very culturally-based thing, though, and you might get a different response elsewhere. I don't know what research has been carried out around the world. d  SignaturePearce Consulting http://www.pearce.uk.com > First the sound level your hear from of your loudspeakers is dependent on > their capablity, the power provided, the distance you are from them, the [quoted text clipped - 11 lines] > the sound, or if you want it to sound twice as loud, you need 10 times as > much sound. Not necessarily, it depends on the frequency of the tone as well as the amplitude. Our hearing is nonlinear both in amplitude and frequency. Depending on the frequency, as little as 4 to 6 dB difference will result in an apparent doubling of halfing of the perceived volume. It is also dependent on the initial level as well. > Not necessarily, it depends on the frequency of the tone as well > as the amplitude. Our hearing is nonlinear both in amplitude and > frequency. Depending on the frequency, as little as 4 to 6 dB > difference will result in an apparent doubling of halfing of the > perceived volume. It is also dependent on the initial level as well. That's interesting. Can you turn the volume of your radio set to the point where it's double as loud? Than you are no musician. :-) >> Not necessarily, it depends on the frequency of the tone as well >> as the amplitude. Our hearing is nonlinear both in amplitude and [quoted text clipped - 4 lines] > That's interesting. Can you turn the volume of your radio set to > the point where it's double as loud? Than you are no musician. :-) The point here is perceived loudness, you most certainly can turn your radio up to the point that it seems twice as loud, assuming that your radio has enough power output. It has absloutely nothing to do with whether you're a musician or not. >> First the sound level your hear from of your loudspeakers is dependent on >> their capablity, the power provided, the distance you are from them, the [quoted text clipped - 17 lines] > in an apparent doubling of halfing of the perceived volume. It is also > dependent on the initial level as well. Correct. I did specify 1000 Hz and say "approximately." >> First the sound level your hear from of your loudspeakers is dependent on >> their capablity, the power provided, the distance you are from them, the [quoted text clipped - 17 lines] >an apparent doubling of halfing of the perceived volume. It is also >dependent on the initial level as well. Thats interesting. Less than doubling the amplitude will sound like doubling the amplitude. Sure, there are errors in our judjment. greg >>> First the sound level your hear from of your loudspeakers is dependent >>> on [quoted text clipped - 26 lines] > doubling the amplitude. > Sure, there are errors in our judjment. Not exactly, even 4dB is more than doubling amplitude, 6dB is quadrupling the amplitude. Because of the ninlinearity in our hearing, doubling the amplitude won't cause an apparent doubling of the volume. Typically, apparent doubling of the volume requires from four to ten times the amplitude of the original signal, depending on frequency and amplitude of the original. >>>> First the sound level your hear from of your loudspeakers is dependent >>>> on [quoted text clipped - 33 lines] >amplitude of the original signal, depending on frequency and amplitude of >the original. I would have to dissagree. 6 dB is quadrupling the power. Power varies as voltage or amplitude squared. greg >>>>> First the sound level your hear from of your loudspeakers is dependent >>>>> on [quoted text clipped - 45 lines] > I would have to dissagree. 6 dB is quadrupling the power. Power varies > as voltage or amplitude squared. Since the discussion was about sound level or volume, the references would be dB SPL (Sound Pressure Level), not voltage or amperage. Thus the amplitude would be expressed in dB SPL. > Not exactly, even 4dB is more than doubling amplitude, 6dB is > quadrupling the amplitude. Because of the ninlinearity in our hearing, > doubling the amplitude won't cause an apparent doubling of the volume. > Typically, apparent doubling of the volume requires from four to ten > times the amplitude of the original signal, depending on frequency and > amplitude of the original. +6dB means always doubling (!) the sound pressure amplitude. Interesting that you can decide when your sound is double as loud. I know when it's louder, but I have no meter in my brain to know when it's exactly twice as loud. I also do not know when my coffee will be double as warm. Cheers Jens > Interesting that you can decide when your sound is > double as loud. I know when it's louder, but I have no > meter in my brain to know when it's exactly twice as loud. > I also do not know when my coffee will be double as > warm. I totally agree. The brain has no "meter scale" from which to read the response as a number of ANY of our senses, hearing included. I have no concept of "exactly N times as loud". Or hot, bright, heavy, whatever. I have had this argument on usenet before, years ago, and people insisted I must be somehow disabled or something for not being able to judge "exactly twice as loud". I am tempted to say that people who claim to be able to do it are deluding themselves or attempting to delude others. At best, with practice, it might be possible to kind of "learn", but that would be very much a practice-related skill. It is NOT an inherent skill or ability we have, IMNSHO. Martin SignatureM.A.Poyser Tel.: 07967 110890 Manchester, U.K. http://www.livejournal.com/userinfo.bml?user=fleetie >> Interesting that you can decide when your sound is >> double as loud. I know when it's louder, but I have no [quoted text clipped - 11 lines] > insisted I must be somehow disabled or something for not being able > to judge "exactly twice as loud". The scientists who came up with this surveyed many people to get what the "average" person would consider to be a doubling or halving of perceived volume. I'm not aware of any use of the word "exactly" in connection with this work, after all it was concerning the apparent perception of volume level. > I am tempted to say that people who claim to be able to do it are > deluding themselves or attempting to delude others. If they were using the word "exactly" in their discription, I would be inclined to agree. However, people are individuals and have different perceptions of volume level. The research was conducted with many different people, and the conclusions were based on the majority opinion. That is another reason why the range is 4 to 10 dB. > At best, with practice, it might be possible to kind of "learn", but that > would be very much a practice-related skill. It is NOT an inherent skill > or ability we have, IMNSHO. The people being surveyed were not, for the most part, trained listeners, the whole thing was based on what the average person would perceive as being twice as loud or half as loud. Perception is how we get an idea of what is going on around us, and I believe it is indeed based in inherent ability to perceive. I'm sure that much of how we describe what we perceive is learned, just as we learn to talk, read, and every other thing we do that requires perception of what is around us. If you leave out the word "exactly", your argument has no merit. Simply put, the majority of people can discern what, to them, is a doubling or halving or apparent volume. If you can't then you're not a member of that majority. Was there some other point that you were trying to make? >> Not exactly, even 4dB is more than doubling amplitude, 6dB is >> quadrupling the amplitude. Because of the ninlinearity in our hearing, [quoted text clipped - 12 lines] > > Cheers Jens A 6 dB increase in SPL would be a quadrupling in acoustic power, not a doubling. A 10 dB increase would require ten times the acoustic power. Since we were talking about the apparent doubling in loudness as perceived by a person, I don't see what you're getting at. >>> Not exactly, even 4dB is more than doubling amplitude, 6dB is >>> quadrupling the amplitude. Because of the ninlinearity in our hearing, [quoted text clipped - 17 lines] > Since we were talking about the apparent doubling in loudness as perceived > by a person, I don't see what you're getting at. I think he is taking the position that the "amplitude" refers to the amplitude of the actual pressure wave which does double when the power or pressure squared quadruples. Since Sound Pressure Level (SPL) is based on pressure squared (a powerlike quantity), then a 6 dB increase in SPL or power corresponds to a doubling of the pressure amplitude though it is a quadrupling of the sound power. >>>> Not exactly, even 4dB is more than doubling amplitude, 6dB is >>>> quadrupling the amplitude. Because of the ninlinearity in our hearing, [quoted text clipped - 24 lines] > power corresponds to a doubling of the pressure amplitude though it is a > quadrupling of the sound power. Sound pressure level is expressed in dB SPL and those are the "dB's" we're referring to when we're talking about differences in perceived volume, we are talking about relative power levels, not the amplitude of the pressure wave, so for the sake of clarity, I think we should stick with power. :-) >>>> Not exactly, even 4dB is more than doubling amplitude, 6dB is >>>> quadrupling the amplitude. Because of the ninlinearity in our hearing, [quoted text clipped - 24 lines] >power corresponds to a doubling of the pressure amplitude though it is a >quadrupling of the sound power. You get the same effect when you place two speakers side by side. With both on, the sound level doubles. It like quadrupling the power level of one speaker. Someone else mentioned this doubling or 10 db effect is level dependant. greg > You get the same effect when you place two speakers side by side. > With both on, the sound level doubles. It like quadrupling the power > level of one speaker. That is a very troulesome example because of the phase coherence between speakers positioned that way: If you played different media at the same power pevel through the second speaker, then the difference heard would be certainly 3 dB. But if you drive the second speaker with the same signal as used for the first speaker, that phase coherence (array effect) will produce identical sound from two different positions, and the directivity afforded by such will cause the sound amplitude to double on a line that is the perpendicular bisector of the line joining the speakers, while 90 degrees from that, being on the extended line between the speakers, a lesser sound level will be heard since patrial cancellation occurs. Even more perlexing is the the degree to which the sound level increases when the speakers are very close together. The way I have rationalized this dual-speaker conundrum is that only by intgrating the pressure squared over the entire hemisphere or sphere surface containing the speakers will one have a predicable result; the sound power so determined will be the sum of the sound powers emitted by each sppeaker. Such secondary speakers are not usually used next to one another unless an "array" effect in a specific direction is desired. Secondary speakers are usually placed at different locations (aka "slave" speakers) to send sound to other parts of a room where the sound level from the distant first speaker is indufficient. Angelo Campanella > > You get the same effect when you place two speakers side by side. >> With both on, the sound level doubles. It like quadrupling the power [quoted text clipped - 26 lines] >sound to other parts of a room where the sound level from the distant >first speaker is indufficient. I fully agree. We would never be able to achieve concert levels with speakers unless they summed and increased overall efficiency. Using the two speaker example shows a couple of neat things. Of course, when designing speakers, using multiple drivers in one cabnet will have predictable outputs. If you don't know the rules, things will just not work out right. greg > Not exactly, even 4dB is more than doubling amplitude, TILT! Bad terminology. Amplitude squared is energy. 3dB is a doubling of energy; a 40.4% increase in amplitude. > 6dB is quadrupling the amplitude. TILT! again. > Because of the ninlinearity in our hearing, doubling the > amplitude won't cause an apparent doubling of the volume. Typically, > apparent doubling of the volume requires from four to ten times the > amplitude of the original signal, depending on frequency and amplitude of > the original. Change all your "amplitude"s to "energy". Angelo Campanella >> Not exactly, even 4dB is more than doubling amplitude, > [quoted text clipped - 16 lines] > > Angelo Campanella You're right Angelo, the term "amplitude" isn't the best term, "energy" is much better. Of course, I was referring to the "amplitude" of the power level. :-) > You're right Angelo, the term "amplitude" isn't the best term, > "energy" is much better. Of course, I was referring to the > "amplitude" of the power level. :-) I am not quite sure. The power (intensity) cannot be sensed by a simple microphone nor by our ears. Really! And it would not be valuable in music recording if it could. So I have another feeling of amplitude. :-) Cheers Jens >>> Not exactly, even 4dB is more than doubling amplitude, >> [quoted text clipped - 17 lines] >> >> Angelo Campanella > You're right Angelo, the term "amplitude" isn't the best term, It's not that "amplitude" isn't the best term, it's that it's a technically incorrect term. > "energy" is much better. Of course, No, "energy" isn't much better, it's technically correct. I was referring to the "amplitude" of the power level. :-) There is no such thing, and you are in serious need of both a technical education and a technical dictionary. Obviously things are slow in alt.music.home-studio, so you come here pretending to be knowledgeable, but all you do with your unbounded technical ignorance is confuse those seeking truth. Your technical ignorance and your reputation as a technically-inept bulshitter is well known outside this newsgroup. In fact, Jim Carr created a web page in your honor. http://www.azwebpages.com/porky.htm No doubt, "Porky on dBs" will be a welcome and informative addition to "The Porky Page." |
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