Morricab,
1. It seems we have different understandings about noise floors. I don't believe for one second the noise floor is determined by the loudest noise source, nor have I ever heard of this definition before. Especially since there are audible noises scattered throughout the frequency spectrum, some which may be intentional, some that come and go, and others that remain constant. Moreover, I'm convinced that our sensitive electronics are or should be indiscriminate between audible noise and music, as it's all just info being processed - If that's even a point worth mentioning here. Regardless, some claim (and I agree) that the worst distortions (noise) that most greatly harm our playback systems are those distortions / noises which cannot be heard and according to some cannot be measured, yet these same inaudible distortions (noise) are perhaps the greatest contributor to determining the noise floor level.
2. In light of my response above (#1) and the claim that a signal cannot be measured below the noise floor. Supposedly tape hiss is somewhere in the range of 500Hz - 2500Hz. Hence, if I'm correctly understanding your claim that the loudest noise determines the noise floor level, then there's much music info in the lower regions that cannot be measured if tape hiss is present. That's just odd to me.
With regard to noise floor topic in general, I'm just gonna stick with Wikipedia's definition, which in my endeavors seems very consistent with the simple understanding I've developed over years from others I consider to be in-the-know about this subject.
3. Regarding Curl's admission. You were not present for any part of that lengthy discussion spanning several months. Hence you have no awareness of the context of the topic of discussion (the OP), nor do you have any awareness of the context for the given time/day for which Curl made this admission. As such I'm quite confident you took and continue to take Curl's admission completely out of context. I already tried once to correct you about this but you continue to respond without seemingly taking this in the limited context I tried to convey.
Try this out (see the link). As you can see, the highest noise in your system will determine approximately the noise floor. Even if you have 4 sources of noise at 30db each the combined noise will be 36db. If only one is at 30db and the rest are 10db or more lower then you have only about 31db...effectively the same loudness as the loudest noise.
http://www.snapfour.com/combinednoise_calculations.aspx
of course this is probably assuming white or pink noise that are more broadband.
From Noise (wikipedia):
"From a physics standpoint, noise is indistinguishable from sound, as both are vibrations through a medium, such as air or water. The difference arises when the brain receives and perceives a sound." Perception is the key.
"In audio engineering, noise can refer to the unwanted residual electronic noise signal that gives rise to acoustic noise heard as a hiss"
From Noise Floor (wikipedia)
"In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system, where noise is defined as any signal other than the one being monitored."
However, as I demonstrated with calculator up there, the addition is not linear so the loudest noise source has by far the biggest impact on the total noise level and is essentially the noise floor.
"If the dominant noise is generated within the measuring equipment (for example by a receiver with a poor noise figure) then this is an example of an instrumentation noise floor, as opposed to a physical noise floor."
"and the claim that a signal cannot be measured below the noise floor" I have searched Wikipedia and I do not find this claim anywhere.
In fact I find articles like this:
http://ieeexplore.ieee.org/document/882477/?reload=true
Believe what you want, the facts don't change based on your beliefs:
"Tape hiss is the high frequency noise present on analogue magnetic tape recordings caused by the size of the magnetic particles used to make the tape. Effectively it is the noise floor of the recording medium. It can be reduced by the use of finer magnetic particles or by increasing the amount of tape used per second to record a signal. It can also be reduced by increasing the track width of the recording. A 3 dB reduction in hiss occurs for every doubling of the track width." It doesn't matter so much about lower frequencies since your hearing sensitivity is lower. Tape hiss is right in the prime hearing region. Nevertheless, you can still hear sounds softer than that...even in that frequency range.
Well, I really don't care about Curl's admission to be honest...I never liked the sound of any of his gear designs anyway.
