The Sound Sweep by J. G. Ballard

The Sound Sweep by J. G. Ballard (Science Fantasy #39, February 1960) opens with Madame Gioconda, an ageing and out of work opera diva, suffering a headache which is worsened by the sounds of flyover traffic and then, later, by the phantom applause that comes from the auditorium around her apartment on the sound stage of a disused radio station—applause that later turns into boos and catcalls. At midnight a man called Magnon, a mute who can “hear” sound residues, arrives with his “sonovac”:

Understanding her, he first concentrated on sweeping the walls and ceiling clean, draining away the heavy depressing underlayer of traffic noises. Carefully he ran the long snout of the sonovac over the ancient scenic flats (relics of her previous roles at the Metropolitan Opera House) which screened-in Madame Gioconda’s makeshift home—the great collapsing Byzantine bed (Othello) mounted against the microphone turret; the huge framed mirrors with their peeling silverscreen (Orpheus) stacked in one corner by the bandstand; the stove (Trovatore) set up on the program director’s podium; the gilt-trimmed dressing table and wardrobe (Figaro) stuffed with newspaper and magazine cuttings. He swept them methodically, moving the sonovac’s nozzle in long strokes, drawing out the dead residues of sound that had accumulated during the day.
By the time he finished the air was clear again, the atmosphere lightened, its overtones of fatigue and irritation dissipated. Gradually Madame Gioconda recovered. Sitting up weakly, she smiled wanly at Mangon. Mangon grinned back encouragingly, slipped the kettle onto the stove for Russian tea, sweetened by the usual phenobarbitone chaser, switched off the sonovac and indicated to her that he was going outside to empty it.  p. 205 (The Year’s Best SF #5, edited by Judith Merril, 1961)

When Magnon empties the sonovac there is only the usual sound detritus, and it becomes obvious that the audience that Madame Gioconda claims to hear is only imaginary. But Magnon is an admirer of the singer and hopes to win her favour—he visits every day to clean the apartment of sound residues, serve her tea, and listen to her tales of a comeback and revenge—so he keeps this information to himself.
In the next part of the story we learn more about her obsolescence (normal music was replaced by ultrasonic music which can’t be heard by humans but has an emotional effect) and her plans to stage a comeback by blackmailing a wealthy producer called LeGrande who is going into politics (she drunkenly relates she has intimate photographs of them together as well as a “no holes barred” memoir).
The rest of the story follows quite an involved plot, which adds another character, Ray Alto, a client and friend of Magnon’s who is an ultrasonic composer, and Madame Gioconda’s discovery of the fact that Magnon can not only hear sound residue but can distinguish snatches of conversation. This latter ability eventually sees Magnon and Madame Gioconda go the “sound stockades”—a dumping ground for all the city’s sonic waste—and sieve through the detritus for fragments of conversation which will let them blackmail Le Grande. During this search Magnon recovers his powers of speech.
All of this eventually rolls towards a climax where (spoiler) Madame LeGrande is scheduled—after her blackmail attempt is successful—to sing alongside a debut performance of Alto’s ultrasonic Opus Zero, much to the composer’s fury. Alto then plots with Magnon (who has subsequently been brutally snubbed by Gioconda after she got what she wanted) to hide a sonovac at the performance to hoover up her voice before it gets to the mike (a voice which sounds like, according to Alto, a “cat being strangled” because “what time alone hasn’t done to her, cocaine and self-pity have.”) But, of course, during the performance Magnon (who has by now lost his voice again) decides to revenge himself by letting the world hear her:

Mangon listened to her numbly, hands gripping the barrell of the sonovac. The voice exploded in his brain, flooding every nexus of cells with its violence. It was grotesque, an insane parody of a classical soprano. Harmony, purity, cadence had gone. Rough and cracked, it jerked sharply from one high note to a lower, its breath intervals uncontrolled, sudden precipices of gasping silence which plunged through the volcanic torrent, dividing it into a loosely connected sequence of bravura passages.
He barely recognized what she was singing: the Toreador song from Carmen. Why she had picked this he could not imagine. Unable to reach its higher notes she fell back on the swinging rhythm of the refrain, hammering out the rolling phrases with tosses of her head. After a dozen bars her pace slackened, she slipped into an extempore humming, then broke out of this into a final climactic assault. Appalled, Mangon watched as two or three members of the orchestra stood up and disappeared into the wings. The others had stopped playing, were switching off their instruments and conferring with each other. The audience was obviously restive; Mangon could hear individual voices in the intervals when Madame Gioconda refilled her lungs.
[. . .]
Satisfied, he dropped the sonovac to the floor, listened for a moment to the caterwauling above, which was now being drowned by the mounting vocal opposition of the audience, then unlatched the door.  pp. 242-243 (The Year’s Best SF #5, edited by Judith Merril, 1961)

This is an original piece and a pretty good one too. I note, however, that it feels like early Ballard: not only does the sonovac and ultrasonic music subject matter feel more like something you would find in Barrington Bayley’s later work, but the story also has a conventional plot. That said, it does have Ballard’s distinctive style.
If the final scene had been clearer, and the miraculous speech recovery in the middle of the story less awkwardly placed, I would have probably rated this higher. That said, these are minor criticisms, and it is well worth a read.
I note in passing that there are a significant number of drug references for the time.
***+ (Good to very good). 14,500 words. Story link.