On 07/21/2010 07:24 PM, Fons Adriaensen-2 wrote: > On Thu, Jul 22, 2010 at 01:05:01AM +0200, Philipp Überbacher wrote: > > > I think the word loudness is a problem here. Afaik it usually refers to > > how it is perceived, and twice the amplitude doesn't mean twice the > > perceived loudness. It may mean twice the sound pressure level, energy, > > or intensity (if we ignore analogue anomalies, as you wrote in some > other > > answer). > > Subjective loudness is a very complex thing, depending on the > spectrum, duration, and other aspects of the sound, and also > on circumstances not related to the sound itself. > > For mid frequencies and a duraion of one second, the average > subjective impression of 'twice as loud' seems to correspond > to an SPL difference of around +10 dB. > > I often wondered what criterion we use to determine which > objective SPL difference sounds as 'twice as loud'. We don't > have any conscious numerical value (there may be unconscious > ones such as the amount of auditory nerve pulses, or the amount > of neural activity), so what it this impression based on ? > > The only thing I could imagine is some link with the subjective > impression of a variable number of identical sources. For example > two people talking could be considered to be 'twice as loud' as > one. But that is not the case, the results don't fit at all (it > would mean 3 dB instead of 10). >
Hi Fons, I'm a fool to even try to answer this question. But I couldn't resist... Let's suppose we have two sounds A and B, and sound B has been measured as being twice as loud as A, by somebody. In order to be able to say that, that person needs some kind of reference measurement unit, the equivalent of a measurement stick. That unit has to satisfy two requirements. It has to be big enough, so that people can agree some difference is being measured, and it has to be small enough, so that a multiples of that unit fit into a realistic range. There is a requirement of maximum precision (the smallest value we can measure), and a requirement of minimum precision. The question is, what kind of measurement stick is being used by that person. First of all, we can assume that the length of that stick will be depend on the range of possible input values that we observe, and that we want to measure. If we want to measure the size of a road, we will probably use kilometers, instead of meters. In the same way, when our ears want to measure the amplitude of a sound, our ears will use smaller or bigger units, depending on the ranges observed. What are the ranges we observe? Let's assume that humans are perfect, and observe everything that we can observe with SPL meters. We could do a statistical investigation on a number of people, and make charts of everything they hear. In these charts we would see what frequencies they are exposed to, and what the minimum and maximum SPL's are for that frequencies. After more analyses, we would have one chart that could be representative for most people. >From that chart we could get an estimate of the size of the measurement unit. Frequencies with with bigger SPL variations would be measured with bigger units, and visa versa. And from this we could deduce what the minimum precision is for a certain frequency, when we say it is twice as loud. To satisfy the requirement of maximum precision, we should take into account the smallest observable differences for every frequency in the spectrum. now you can kill me :-) Greetings, Lieven
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