I have always believed that the harmonic profile as viewed on the vintage swept-tuned spectrum analyzers like the HP 3580A or the modern day PC based FFT analyzers, gives us an analytical view into, "how things sound" and in the case of this video, documents the nuances between different tubes of the same class. Furthermore, every since I have gotten into spectral analysis, I believe we can analytically capture the nuances between virtually everything we hear from the voice of a child, a woman, a man and even the meow of different cats. Very subtle differences in the harmonic profile can alter the sound significantly. These tubes documented could appeal to different styles of musician depending on their musical creation and volume level. Hope you find it interesting and valuable.