" Now the biologists just need to find another physiological system that turns music into biological energy and we might have audiosynthesis :-) I don't really know how photosynthesis works so I am a little hazy how audiosynthesis might work. Nice idea, though, gaining sustenance from music. Not sure I'd agree with your idea in Earthsong that the PTB would try to get rid of it however."
Audiosynthesis -- which is the idea that human beings could get all their nourishment from sound in a fashion analogous to plants getting their nourishment from light -- was a major plot element in Earthsong. I got the idea from four things that came my way, serendipitously, one after another, over the course of a few months.
First I listened to an audiotape -- the name and author of which I no longer remember -- presenting the hypothesis that human beings would eventually evolve into organisms that would live by photosynthesis the way plants do. It was interesting, but struck me as improbable given the dangers of extensive exposure to sunlight for humankind.
Then I read an account of the famous episode of Paris doctor Alfred Tomatis and the monks of the Benedictine Abbey of Bec-Hellouin (at Solemne, France). Sometime in the 1960s a new administrator at the abbey made what he thought would be a positive change in the monks' regime. They had all been doing 8 hours a day of Gregorian chant, spread out over the day; he thought that was a waste of time and ordered the practice discontinued. Within a short time, the monks began to slip into a severe "failure to thrive" state; they were weak and listless and depressed and exhausted. Various doctors were called, and found no explanation for the problem; they explained to the administrator that good health for those monks was impossible on the the energy balance in their regime -- that is, the monks were expected to do more work than was possible given the amount of food that was being provided to them. But when the doctors were reminded that the regime had been working perfectly well for many many years, they couldn't explain that either. All very difficult -- until Dr. Tomatis was called in, and he ordered the 8 hours a day of chant restored, after which all the monks gradually recovered and went on about their business. [So far as I can tell, googling this today just gets you lots of pages on "The Tomatis Method" with only an occasional sentence or two about this episode, so I won't try to provide a link.]
The third thing was all the stories about religious personages from various faiths who are alleged to have lived most of their lives in good health on almost no food at all ..... only the wafers taken at Communion, for example, or only one tiny bowl of plain rice each day. Ordinarily, the figures in these stories lived in situations where there was a whole lot of chanting and/or singing going on.
Finally, there was the fact that the "epidemic" of obesity in the United States coincided with the arrival of technology that made music available inexpensively to almost anyone, in abundance .... cheap radios, cheap tape players, and the like. Suddenly you didn't have to be rich to listen to hour after hour of music. I put all this together, and got audiosynthesis.
I'm convinced that the Powers That Be would do everything possible to stamp out audiosynthesis if such a thing were ever proposed in the real world. The economic consequences of human beings no longer needing "mouthfood" would be unthinkable. No more agricultural industry. No more food industries. No more agencies regulating food. No more need for stoves and garbage disposals and dishes and pots and pans and cutlery. No more restaurants. Vast reduction in the need for trucks to haul things. It would be an economic catastrophe. It's the sort of situation that leads to scenes in novels where somebody in charge orders the scientist(s) killed and every trace of their discovery destroyed. (With genteel regret, of course.) I don't think that the PTBs would be able to stamp it out if -- as in Earthsong -- audiosynthesis were already widely practiced before they found out about it; hunger is highly motivating. But if they could nip it in the bud? I don't think they'd hesitate even long enough to pay lip service to the idea that ending human hunger would be good and noble.