From the Etymotic website:
Target Curve Explained
Target curves on Etymotic frequency response accuracy graphs define 100% accuracy as the open ear diffuse-field response of the KEMAR manikin, modified to compensate for the high frequency boost added to high-quality recordings. This modification (approximately 5 dB at 10 kHz) is necessary to avoid earphones sounding too bright on commercial recordings. Commercial recordings have a high-frequency boost that compensates for the high frequency roll-off in studio monitor loudspeakers and high-quality stereo loudspeakers and earphones.
Perhaps I am reading/interpreting this wrong but I am confused in two regards.
1) If the curve goes up on the right side (as it does with ER4) isn't this boosting the high frequency? The point above leads me to think that commercial recordings are already high frequency boosted and the Ety "modification" is to tame it down some (5 dB). Is this correct?
2) If it is correct and Ety is taming down that natural high frequecy boost, how come they STILL reveal more high frequecies than any other IEM by a long shot?
Also I think the treble extension is good for an iem, particularly at that price point. But it's not better than, say my ck100. It's just more emphasized and colored, to the point that there's a high frequency glaze covering up the other frequencies. And there is no comparison between er-4 treble extension and that of a full-sized phone like the k701s or lambda.