Originally Posted by: hifistan 
"These are what I understand (and I have been known to make errors) are the current thinking with regard to hearing . Firstly all of us have an individual and unique physical hearing system . No two head shapes , ear shapes and inner ear shapes are identical . Secondly how the sound we hear is routed and then differentiated by the brain is again unique for each individual . So when you say this sounds different to me you are completely correct it does . it is also therefore equally true that no one and I do mean no one can tell you what you hear only you can tell other people what you hear."
When I was doing my PhD research in the early 70s the distinction between retinal images and perceptions was well known. If we ask if two people "see" the same thing we must distinguish between whether we mean that the same pattern of photons form on their retina or that the brains of the two interpret them in the same way. In the first case they do "see" the same thing; in the second they do not. A whole chain of processes exist between the raw image and the perception. The same thing would seem to apply to hearing. The sound waves hitting the eardrum may be identical/very similar but they undergo extensive processing before we "hear" the sound.
In a totally different direction I wonder to what degree designers employ blind testing in developing their products. And at what stage do they use it? I actually knew a speaker maker who used no testing whatsoever; if it was right in theory it had to be right in practice. But that is another story entirely.
I can't speak for others but when I was designing active speakers we definitely did do blind testing. And by designing the test properly one can show that some "perceptions" are all in the imagination and some are real. And in general, amplifier design is so much an established art that any competent designer working in this field can produce an amplifier whose deviations from accuracy are so small that they are literally imperceptible. When designing active speakers it is easier than normal to carry out proper blind testing simply because the amplifiers themselves are completely invisible to the listener.
As you say, in general, when we say we "hear" something we actually mean we "think we can hear" something. And when we want to compare audio products it is self-evident that the actual identities of the compared items MUST be hidden from the listener, and also that listening levels MUST be standardised (Fletcher-Munson etc having shown that the perception of tonal balance depends critically on level). Otherwise we are just describing how the interactions of a host of inputs to the mental process, including price, appearance, manufacturer's name, claimed design techniques, pre-existing beliefs, knowledge of any modifications and the claimed benefits/demerits of those modifications, etc etc are processed with the actual stimulus to the ear to produce a "perception" of audio quality.
And this is just the minimum condition for a valid test - quite evidentally a single comparison could produce a perception of difference which is purely due to chance, especially when the listener already holds the belief that there will be a difference, and statistically valid repeat techniques will have to be used to see if it is genuine. In fact there are far better techniques which apply uniquely to amplifiers (both pre and power) where you amplify the error between input and output with the same electrical-to-acoustic gain as the original stimulus and show that the error is completely inaudible, regardless of its measured level.
Equally you can show that an amplifier's response to mechanical vibration is (or isn't) totally inaudible. With the particular amplifiers I carried out these tests on - a thing I was initially worried about due to the high vibrational levels with amplifiers actually mounted within speakers - I was able to show that this response was both measurably and audibly imperceptible. A thing I can confirm with my later work with electronic systems mounted directly on oil-rig drill-heads, high-speed gas pumps etc. If tests on things like anti-vibrational feet for HiFi amplifiers produce audible results on reviews then this is the stimulus for producing condemnation of the amplifier designer for his failure to have grasped the most basic requirements for an audio amplifier, not praise for the designer of the feet - especially when you read the advertising puff for these feet, with in virtually all cases a complete lack of grasp of even the most basic theory of mechanical design.
