The great lost debate between Koenig and Helmholtz on a continuous tone complex harmonic phase shift - it is audible or not? Threshold Shift

 The "Magic of the Senses" image I show on my blog is for a "continuous tone" phase shift - as explained in the book on sound and video production

So it was done by Helmholtz originally but Koenig claimed otherwise - that the phase shift could be heard.

This book explains the debate and a set of experiments to set the record straight 

And Helmoltz won the debate - via the experimental results.

What's interesting is that with the phase shift - the octave would sometimes disappear while the Perfect Fifth or third harmonic could always be heard.

The original "Phase shift" experiments were done by Lord Kelvin using tuning forks and then just adjusting the weights of the tuning forks.

But now more recent experiments claim Helmholtz really was wrong

 The issue is that they used head phones but claim if the sound was listened to in a room then the phase change probably would not be very noticeable...

So then Threshold Shift was introduced as a concept to resolve the debate.

So that experiment proved once again that as the octave is phase shifted then the fundamental frequency can be made to vanish. The key point of Helmholt - as shown in the "Magic of the Senses" phase shift is s that the perfect fifth is phase shifted as a Perfect Fourth that then becomes the NEW octave while the original octave cancels out the first fumdamental! So then you have the same Perfect Fifth remaining only it is an inverse as F to the octave C instead of  fundamental C to the G Perfect Fifth.

So Helmholtz's genius was to argue that it's in no way due to the phase change but rather due to the relation of the common overtones of the harmonics. This is precisely what the noncommutative phase claim is - that the time-frequency uncertainty arises from the noncommutative phase since the Perfect Fourth is never the natural overtone of the fundamental frequency.

The Fifth is a compound tone in which the second partial is the third partial of the fundamental compound tone; the Fourth is a compound tone in which the third partial is the same as the second of the Octave.

p. 255

On the Sensations of Tone as a Physiological Basis for the Theory of Music

Hermann von Helmholtz

Longmans, Green, 1912