“Look here,” Nash indicated three six-foot long prints. “This represents part of a single sound pronounced by Dorna Guiselle and Miss Wentworth. It was recorded by the ‘fulltone’ process having an effective response up to twenty thousand cycles per second. See the difference?”

(The perfect voice from 'Prima Donna 1980' by Bernard Brown)

The doctor nodded.

“Dorna Guiselle’s is more peaky. I suppose that is due to your precious harmonics?”

“Yes, yes of course. But don’t you see the significance?” Then as the doctor merely stared, “The full line is the fundamental wave and the dotted one the mean through the harmonic area above the fundamental. You must be blind, man, if you don’t see the dotted lines are similar and both reduce to the same curve! Plotted to a common base they show only difference due to experimental error.” His forefinger pointed out a lower curve under which was printed “Harmonic Indicator”. This curve can be derived from either the voice of Dorna Guiselle or Wentworth — it is common to them both. There, from either voice I am given a factor which will enable me to choose harmonics from records of the other.”

“You’ll have to explain further, I’m afraid,” remarked the doctor drily. He did not like the way Nash referred to Joyce Wentworth.

Nash almost danced in impatience.

“Harmonics are expression, emotion — joy, sorrow, hate, love, greed and all the rest of them. The curve of the harmonic indicator is the curve of emotion. Wentworth sings into the microphone. I filter off the harmonics, leaving the fundamentals below, say 1,200. The harmonics are automatically integrated by light before a photoelectric cell, which gives pulses proportional to emotion, expression or whatever you like to call it.

“These, after suitable amplification, are impressed as a modulator upon a very delicate oscillator having a range from 1,200 to 20,000 cycles per second, which thus differentiates the flat curve into its component fre- quencies. The resultant speech current is then added to the fundamental from Wentworth and the composite current goes to the main soundcast amplifiers.

“Aren’t you as badly off as you were at first?” asked the doctor with a puzzled frown. “You seem to have cut off the top of Miss Wentworth’s voice and then elaborately put it back again.”