gregorio
Headphoneus Supremus
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The general question is "Do A and B sound different?" and how we go about answering that. Let's assume they are definitely different signals.
OK, we'll assume that for the sake of taking the argument further, even though it's not an assumption we should generally make because there are many circumstances where identical signals can be perceived as different.
Originally Posted by johncarm /img/forum/go_quote.gif
What calculations do you use to reduce that continuous signal to a single number, -100 dB?
As I've mentioned (twice now), a null test. Assuming the signals are not identical, the result of a null test will be the difference between the signals. We can now record and then measure this resultant signal as we can any other. Which, also for the sake of argument, we'll say is -100dBFS.
You said that the differences might be audible if the difference is greater than that, depending on the part of the spectrum. That sounds like you are referring to theories about thresholds of audibility, correct?
No, we can just as easily turn the argument on it's head and arrive at the answer that way. For example, to be able to identify a signal, the signal obviously needs to be at or above the level of any background noise. If the level of background noise in the average sitting room is say 50dBSPL then the level of our (difference/null result) signal needs to be at least 50dBSPL. If our difference signal is at 50dBSPL and peaks at -100dBFS, the peak (0dBFS) level of our original signal/recording would therefore be 100dB higher, at 150dBSPL. Few, if any, consumers have a system capable of at least 100dB of dynamic range and a peak output of 150dBSPL at the listening position but even if they did, 150dBSPL would cause physical damage to some of the structures in the human ear. Models of the threshold of audibility are therefore unnecessary in this example, knowledge of sound science and human ear physiology are enough to arrive at the "truth", without recourse to any type of listening test which at best would only provide a certain probability of arriving at the "truth"!
G