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Constant spectrum melody

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Constant spectrum melody

 



A constant timbre at a constant pitch is characterized by a spectrum. Along a piece of music, the spectrum measured within a narrow time window varies with the melody and the possible effects of instruments. Therefore, it may seem paradoxical that a constant spectrum can be perceived as a melody rather than a stamp.

 


The paradox is that the ear is not an abstract spectrograph: it "calculates" the Fourier transform of the sound signal in a narrow time window, but the slower variations are seen as temporal evolution and not as pitch.

 


However, the example of paradoxical melody above contains no infrasound (i.e. pure tone of period slower than the time window) ! The second paradox is that when two pitches are very close, they create a beat. If the period of this beat is longer than the integration window, it is seen as a sinusoidal variation in the average rating: sin(2π(f+ε)t) + sin(2π(f-ε)t) = sin(2πft)cos(2πεt), where 1/ε is the slow period.

 


The present spectrum is made of multiple frequencies beating together, resulting in a superimposition of various pitches fading in and out at different moments and pace, thus forming the melody.

 

Constant spectrum melody



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Interesting how little it changes if you play it backwards ...
 

 ydolem murtceps tnatsnoC
 




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Look ... there in the corner of  your eye ... you can see Dog!!   Big Grin
 
 

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Interesting how little it changes if you play it backwards ...
 
It should be identical backwards;  the point of the illusion being that the ear-brain is where the action is (the brain's response to this continuous spectrum is a series of 'phantom' tones that aren't really there)

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Should be identical, but it's not.
 
Or is that an illusion, or am I just delusional?
 
 
 
 

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It's constructive and destructive interference of the sound waves. This is not 'perceived', it happens with all wave activity. 
 
What is perceived is the change in pitch.  The only thing that is changing is amplitude (volume), but your brain perceives it as change to the note (octave).

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It's constructive and destructive interference of the sound waves. This is not 'perceived', it happens with all wave activity. 
 
What is perceived is the change in pitch.  The only thing that is changing is amplitude (volume), but your brain perceives it as change to the note (octave).
 
Right on; I'd add that whether or not the beat frequency is inside or outside of the ear's integration window will determine if the sound at any given point along the scene is perceived as a phase change (outside the window) or a pitch change (inside the window)
 

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