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On 07/21/2010 07:24 PM, Fons Adriaensen-2 wrote:
<blockquote
cite="mid:tag:old.nabble.com,2006:post-29232177@localhost.localdomain"
type="cite"><base
href="http://old.nabble.com/Floating-point-processing-and-high-dynamic-range-audio-tp29226792p29232177.html">
<title>Re: Floating point processing and high dynamic range audio</title>
<base href="http://old.nabble.com/linux-audio-dev-f13235.xml"> On
Thu, Jul 22, 2010 at 01:05:01AM +0200, Philipp Überbacher wrote: <br>
<br>
> I think the word loudness is a problem here. Afaik it usually
refers to <br>
> how it is perceived, and twice the amplitude doesn't mean twice
the <br>
> perceived loudness. It may mean twice the sound pressure level,
energy, <br>
> or intensity (if we ignore analogue anomalies, as you wrote in
some other <br>
> answer). <br>
<br>
Subjective loudness is a very complex thing, depending on the <br>
spectrum, duration, and other aspects of the sound, and also <br>
on circumstances not related to the sound itself. <br>
<br>
For mid frequencies and a duraion of one second, the average <br>
subjective impression of 'twice as loud' seems to correspond <br>
to an SPL difference of around +10 dB. <br>
<br>
I often wondered what criterion we use to determine which <br>
objective SPL difference sounds as 'twice as loud'. We don't <br>
have any conscious numerical value (there may be unconscious <br>
ones such as the amount of auditory nerve pulses, or the amount <br>
of neural activity), so what it this impression based on ? <br>
</blockquote>
Sorry to post this twice, but I think the mail got truncated.<br>
<br>
Hi Fons, I'm a fool to even try to answer this question.<br>
But I couldn't resist...<br>
<br>
Let's suppose we have two sounds A and B, <br>
and sound B has been measured as being twice as loud as A,<br>
by somebody. In order to be able to say that, that person needs <br>
some kind of reference measurement unit, the equivalent of a <br>
measurement stick. That unit has to satisfy two requirements. <br>
It has to be big enough, so that people can agree some difference <br>
is being measured, and it has to be small enough, so that a multiples<br>
of that unit fit into a realistic range. There is a requirement of
maximum <br>
precision (the smallest value we can measure), and a requirement of <br>
minimum precision. The question is, what kind of measurement stick <br>
is being used by that person.<br>
<br>
First of all, we can assume that the length of that stick will be
depend <br>
on the range of possible input values that we observe, and that we want
<br>
to measure. If we want to measure the size of a road, we will probably <br>
use kilometers, instead of meters. In the same way, when our ears want<br>
to measure the amplitude of a sound, our ears will use smaller or bigger<br>
units, depending on the ranges observed. What are the ranges we observe?<br>
Let's assume that humans are perfect, and observe everything that we <br>
can observe with SPL meters. We could do a statistical investigation<br>
on a number of people, and make charts of everything they hear.<br>
In these charts we would see what frequencies they are exposed to, <br>
and what the minimum and maximum SPL's are for that frequencies.<br>
After more analyses, we would have one chart that could be <br>
representative for most people.<br>
<br>
>From that chart we could get an estimate of the size of the measurement
<br>
unit. Frequencies with with bigger SPL variations would be measured <br>
with bigger units, and visa versa. And from this we could deduce what <br>
the minimum precision is for a certain frequency, when we say it is
twice <br>
as loud. To satisfy the requirement of maximum precision, we should<br>
take into account the smallest observable differences for every
frequency<br>
in the spectrum.<br>
<br>
now you can kill me :-)<br>
<br>
Greetings,<br>
<br>
Lieven<br>
<br>
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