I Can Hear You Whisper by Lydia Denworth

“F.D.—Female, High-Pitched,” and the like, put their lips about three inches from the transmitter and intoned lists of vowel sounds—the “u” of “put,” for example—and words such as “seems” and “poor.” The results established some general characteristics of speech sounds. That the pitch of the voice varies with individuals, for instance. A “deep-voiced man” spoke vowels at about ninety cycles per second—or ninety hertz—and a “high shrill-voiced woman” (F.D. perhaps?) at about three hundred cycles per second. They also noticed that when that same man and woman spoke the “ah” sound in “father,” the wave pictures looked quite different, “yet the ear will identify them as the vowel ‘a’ more than 99 percent of the time.” Whereas two low-pitched male voices pronouncing “i” as in “tip” and “o” as in “ton” create much more similar pictures, “yet they are never confused by the ear.” The Bell team had tumbled to the fact that speech sounds carried some other important characteristic that didn’t show up in the waveform. Later, that characteristic was given a name: timbre.
    Even I, untrained in reading waveforms and spectrograms, could see that the separate sounds in a simple word like “farmers,” casually uttered in an instant, carried detailed and identifiable information that distinguished it from “alters” almost like the fingerprints that distinguish my right hand from my husband’s. The very high frequencies in the “f” and the “s” sounds at the beginning and end of “farmers” are so rapid they look like a nearly straight line. The “a,” “r,” and “m” sounds in the middle show up as peaks and valleys of varying sharpness and depth—the “r” spiking then rolling, spiking then rolling, and the “m” flatter but still undulating like a line of mesas in the desert. All three sounds hovered at the same frequency of 120 cycles per second. The “er” toward the end of the word brought a slight rise in pitch to 130 cycles. “Farmers,” I said out loud. Sure enough, I raised my voice in the second syllable, a fact I had never noticed before. From this work, I could draw a direct line to the audiogram chart Jessica O’Gara had given me, so I could see where the main frequencies of various phonemes in the English alphabet fell.
    Fletcher and his team spent particular time on vowels. Vowels are distinguished from consonants in the way they are formed in our vocal tracts. Critically, they are also at the heart of each syllable. Syllables, I was going to learn, are an essential ingredient in the recipe that allows us to hear and process spoken language. No wonder all languages require vowels. Expanding on Helmholtz’s and Bell’s investigations into the complexities of vowel sounds, the men of Bell Labs identified not just the fundamental frequencies of “ah” and “oo,” for instance, but also the accompanying harmonic frequencies that readily distinguish one sound from the other. From that, they generated tables showing two primary frequencies—one lower, one higher—for each vowel sound. For telephone engineers, such information “makes it possible to see quickly which frequencies must be transmitted by the systems to completely carry all the characteristics of speech.”After World War II, two more Bell researchers were able to use another pioneering device, the spectrograph, to create definitive specifications of vowel frequencies, known as formants. What none of those early researchers could possibly guess was that decades later, a different generation of engineers would use the formant information compiled at Bell Labs to figure out how to transmit the necessary frequencies through a cochlear implant