There was an objection to CDV's recommendation for graphic 
equalisers, on the grounds that a good system should be perfectly flat.

That theory should be right providing that the listener is using 
headphones, or, if using loudspeakers is in an anechoic room (which I 
have heard is psychologically unsettling). Otherwise the most 
non-linear part of the system is the listening room - yes, that is 
part of the system!

Every part of a system has some distortion. Amplifiers introduce very 
little, transducers introduce much more. There is no way to eliminate 
all of it, but it can be minimised. What matters is not so much what 
can be measured by test instruments, but the subjective effect  on 
the listener. Intermodulation distortion can be painful, harmonic 
distortion less so, and some people like or at least tolerate systems 
with a lot of second harmonic distortion - a sort of acoustic octave 
coupler that brightens the sound.

Some people object to CDs because while their distortion is very low, 
it is of an unpleasant nature. LPs and their transducers have much 
higher levels of distortion, but are very much in favour, perhaps 
because the distortion is perceived as enhancing the sound.

So, to the slightly uneven responses of loudspeakers we have to add 
the much larger effect of the listening room resonances. When they 
are taken into account, the response at the listener's seat may be 
very uneven. Equalisers may help to bring the total effect closer to linearity.

Having said all of that, it is unrealistic to expect the result to be 
close to the original sound. What we are concerned with is whether 
the sound of an instrument recorded in its own acoustic can be 
matched by reproduced sound in another acoustic. Tests of 
loudspeakers and live performers behind curtains were once popular 
and blind testing can distinguish between what people hear and what 
they think that they can hear. It is certainly not possible to switch 
the listener blind between home and hall acoustics.

There is also the question of loudness. Do we play music at home at 
the same volume that we hear it at a concert? We know that the human 
ear has an irregular sensitivity at different frequencies 
(Fletcher-Munson and all that) and that changing the volume changes 
the perceived balance between frequencies. That was what the now 
unfashionable "loudness" controls tried to deal with. CDV's graphic 
equaliser can do better than that.

In the end, scientific accuracy is not the goal, but what the 
educated listener enjoys. Obsession with high fidelity can become an 
aim in itself with music used  only to demonstrate equipment. As 
George Ives advised his son Charles, " Don't pay too much attention 
to the sounds - for if you do, you may miss the music."

David

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