ASC President and TubeTrap Inventor, Art Noxon, PE shares his knowledge on the subject. (Originally posted on AVS forum, Dec 2013).
Do Audio Measurements Correlate with Sound Quality?
Sometimes yes, but usually not, depending on the kind or version of the Audio Measurement being made. My primary experience with audio measurement is in the realm of room acoustics so this will be the context of my response to this question.
For 30 years…
…I’ve been seeing that very acceptable acoustic upgrades in a listening room projects might only measure ½ dB reduction in peaks of the frequency response curve, which seems hardly worthy of such an investment. These small reductions in the strength of the peaks in the frequency response curve lie well below the 1 dB threshold of sound level difference and A/B double-blind frequency response listening tests prove inconclusive. If the listener can’t differentiate between the frequency response curve of the room before compared to after the acoustic upgrade….all the while being able to easily differentiate between the musicality of the room before compared to after the acoustic upgrade, then what the listener values in audio performance cannot be can’t really be defined by the frequency response curve in the room.
In other words, if we assume that our golden ear listener is right, that acoustic upgrade did audibly improve the musicality of the sound system in the room but the audio test being used to prove that the room sounds better gives inconclusive results, then the audiophile is not wrong, instead, it is the audio measurement that is wrong.
There is an old adage in statistical measurements: Correlation does not imply causation. Just because two things happen together does not mean one causes the other. When they don’t then these two things remain correlated, in that they do happen at the same time, but only as a coincidence. For example, at noon it is warmer than at midnight. This is a dependable correlation, when one exists the other exists. But the temperature of the day does not cause the clock hands to move and the clock hand movement does not cause the temperature to change. These are coincidentally correlated but not causally correlated. Coincidence does not mean correlation. The goal in correlation measurements is to sort out and find the cause and effect correlation from the coincidence correlations and this is usually not easy, nor obvious.
…we choose and invest in an upgrade and we hope to be able to sit back and enjoy the fruits of our investment. But for some reason, the enjoyment of our upgrade always seems a little sweeter if we can perform an audio test that proves our upgrade can be physically documented. It’s as if we want to hang a plaque on the wall which certifies that our room is better than before, despite that all the while, we know it is better than before. If we want good results, those that correlate with our perception of improved sound quality, we’d better choose a test that correlates with our version of sound quality.