What is the ideal High Freq extension?


I think for a world class system to sound like live music, a good smooth grain free silky (if music calls for) high freq extension is mendatory. But in my mind where the 'flatness' should roll off (at what db rate?)is a big unknown and not quite clear. Is it 10k HZ, 12.5k HZ, 15K HZ or the ideal 20k hz.

This assumes you already have excellent bass extension and mid range.

One would think at ideal 20k hz there will most likely excessive ambience and thinner sound.

What is your opinion?

Thanks.
nilthepill
I have heard speakers with purposed response to 50Khz.While you might not hear that high up,the over-tone structure may be more completely revealed.A lot has to do with the crossover and phase linearity.
You must remember when digital "brick-walled" everything above 20Khz.Thank goodness we got past that!
Nil, I borrowed a hand held spectral analyser with a microphone built in its "nose" cum pink noise generator in a wall wart type of thing. Can't remember the name of it, but it was US-made, if I recall right, had a lot of LEDs in its display. A nifty little thing.
I think spectral analyzer would be more accurate way to measure system system response at your listening position. I think the Ratshake sound meter may not be accurate the freq extremes even with so called corrections applied.

I measured my system response at about 7 ft away (my seating position) and it is RULAR flat ( with corrections applied) from 25 hz to 16 khz. with 2 db boost at 20 hz and 7 db down at 20 kHZ.