“Throw the note over your shoulder!” Debbie Harry, Kathleen Hanna, Justin Vivian Bond and other singers recall Barbara Gustern, a beloved vocal coach who was killed last month at age 87.Barbara Maier Gustern, a 4-foot-11 woman from the tiny town of Boonville, Ind., exerted an improbable and little-known influence over New York’s overlapping music scenes, guiding cabaret performers, stage actors and rock stars to get the most out of their voices.Ms. Gustern, who died last month, had a gift for unusual metaphors that made her teachings stick. In the bedroom of her 17th-floor apartment in the Chelsea neighborhood of Manhattan, where she gave lessons almost every day deep into her 80s, she would ask her students to build theaters inside their heads. Your tongue, Ms. Gustern said, is the stage. Your soft palette is the fly space. You must sing from the very back of stage, projecting your voice into the fly space, through a blowhole at the top of your head.“Your blowhole — these weird little tips that you’re like, ‘That just changed my life,’” said Kathleen Hanna, the frontwoman of the bands Bikini Kill and Le Tigre, who credited Ms. Gustern with restoring her singing voice after medical issues so severe that she thought she might never sing again.The cabaret singer Justin Vivian Bond prepared for a performance at Carnegie Hall with Ms. Gustern’s help. “I filled that room effortlessly, because the inside of my head was basically an extension of the room,” Mx. Bond said.Another one of her students, Tammy Lang, who performs under the stage name Tammy Faye Starlite, said, “Everyone I knew in the downtown scene worked with her. She was the mother to us all.”Her friends and students recalled her as the grandmother who wore dominatrix gear to perform as a go-go dancer at a playwright’s birthday party; who left her friends in the dust as she ran to catch a subway; who danced on top of a table at the cabaret theater Joe’s Pub.Ms. Gustern with one of her star pupils, the performance artist and singer Taylor Mac.Jackie RudinShe had come to the city in the late 1950s with dreams of making it on Broadway. After realizing she wasn’t going to be a star of the stage, she stopped auditioning for parts and dedicated herself to the work that would bring her an unexpected kind of glory.In a recent Facebook post, she wrote that she wanted to die at age 127 by running across the street and accidentally colliding with a Dewar’s Scotch truck. The end came in what appeared to be a senseless act of violence, when someone shoved her to the sidewalk near her home on March 10. The suspect, Lauren Pazienza, who turned herself in almost two weeks after the incident, has been charged with manslaughter.At the time of her death, Ms. Gustern was three days away from recapturing the fantasy of her youth, and returning to the stage.‘Sing It to the Back 40!’Barbara Joan Maier’s family ran a hardware store in Boonville. Bobbi Jo, as she was known, sang at the Methodist church and, as a teenager, taught Sunday school. Later, as a student at nearby DePauw University, she joined the Young Republicans club.Her pursuit of a stage career took her away from all that. She auditioned for parts in New York and joined regional theater troupes along with summer stock companies in the Poconos, landing parts in “The Sound of Music” and “Threepenny Opera.” She traveled the world, a cruise-ship mezzo-soprano.While singing in choirs at a synagogue in the Bronx and a church in Brooklyn, she got to know the man who would become her husband, Josef Gustern, a singer and actor with a bass voice. They married in 1963 and had a daughter, Katherine.While they scrounged to make a living in music, the names of Ms. Gustern’s peers were appearing more and more frequently in Playbill and on Broadway marquees. At around age 40, she faced the fact that she was too old to be cast in lead roles, much less as an ingénue, and she began her next act by taking a job as a teacher at the American Musical and Dramatic Academy in Manhattan. Her husband continued to hustle for stage work, and finally in the early 1990s he scored a long-running part in the Broadway production of “The Phantom of the Opera.”As she settled into the city, Ms. Gustern gained an appreciation for New York’s rough-and-tumble glamour. For some years, prostitutes hung out on the street where she lived, and on morning walks she would try to tell the future by counting the condoms on the sidewalks, as she wrote on her Facebook page, which she treated like a diary. Fewer than three meant trouble; more than three portended good luck; a colored condom indicated that a million-dollar check was on the way; a black one signaled imminent nuclear attack.She began to establish a reputation among insiders of New York’s singing scene in the 1980s, when the avant-garde singer Diamanda Galás took a lesson from her while visiting New York. Ms. Galás ended up moving to the city full-time, in part to keep studying with Ms. Gustern.“Diamanda opened the gate,” said Ms. Lang, the cabaret singer. “And then everybody saw that, ‘Oh, this is somebody who’s open to something that is different.’”Debbie Harry, the lead singer of Blondie, sat in for one of Ms. Galás’s lessons around 1998. Then she began studying with Ms. Gustern. “I had never really tried to learn how to sing properly,” said Ms. Harry, the rare performer who has sung at CBGB and the Café Carlyle. “She taught me more about the voice and your body as an instrument.”Debbie Harry, left, and Ms. Gustern at the Broadway opening of the musical “Passing Strange” at the Belasco Theater in 2008. Ms. Harry credited Ms. Gustern with teaching her “how to sing properly.”Nick Hunt/Patrick McMullan, via Getty ImagesAnother of Mr. Gustern’s students was Murray Hill, an actor, comedian and singer, who spoke at a gathering for her at Joe’s Pub on March 27, after a memorial service at the Church of the Holy Apostles in Midtown. “She was the first, and only, person to say I wasn’t tone-deaf,” Mr. Hill wrote in an email.Tragedy seemed to reinforce Ms. Gustern’s devotion to teaching. In 2003, her daughter died of a drug overdose. Her husband died in 2017. After whole days of lessons, she often spent her nights at students’ performances.Perhaps the biggest job of her career came recently, when she served as the vocal coach for the 2019 Broadway revival of “Oklahoma!” She stayed with the production, which won the Tony Award for best musical revival, until it closed in 2020.“Her career was actually at a high point at 85 years old,” said James Davis, who played Will Parker in the show.During a typical lesson, Ms. Gustern would sit in an antique wooden chair on one side of the bed, a portable keyboard on the blanket before her. The student would stand facing her, on the other side of the bed.“Throw the note over your shoulder!” was one of her catchphrases. Ms. Gustern used bits of Indiana argot to make a point. Rather than telling students to project their voices, she would say, “Sing it to the back 40!” City metaphors crept in, too: “Your mouth is a taxi cab,” she would say, “and your molars are the back doors of the taxi cab. And they’re opening, both of them.”When leading scale exercises, she told her students to use the phrase “he is a really bad bad bad bad man” or the schoolyard taunt “nyah-nyah nyah-nyah-nyah.” She recorded herself going through warm-up exercises and gave the recordings to her students, so that they could practice along with her when they were apart.Ms. Hanna, whose punk style compels her to sing abrasively, said she started meeting with Ms. Gustern more than 10 years ago, after she had undergone surgery on her vocal cords to remove polyps. For a time, her work with Ms. Gustern was her only artistic activity. She learned she had been holding her breath when she should have been letting it go. Under Ms. Gustern’s guidance, she began to exhale before hitting certain notes and to pronounce an ‘h’ before glottal strikes.Ms. Hanna’s voice is back. This month she is starting a tour with her band Bikini Kill. “Without her, I would have been done,” Ms. Hanna said of Ms. Gustern. “How do you thank someone for your career?”Back to the StageBeginning in 2016, Ms. Gustern directed a series of cabaret evenings featuring Austin Pendleton, an actor noted for his character roles in films, and Barbara Bleier, who made her Carnegie Hall debut at age 4. “Make your mouth a little narrower at the top,” Ms. Gustern would comment at rehearsals, and the right rendition of a song would pop out, Ms. Bleier recalled.Now and then Ms. Gustern would perform as part of their show, including a memorable “Santa Baby,” which she sang while making eyes at Ms. Bleier’s husband. But she preferred to remain in the background.That had begun to change in recent months, when she was leading rehearsals for “Barbara Bleier and Austin Pendleton Sing Steve and Oscar,” an evening dedicated to the songs of Oscar Hammerstein and Stephen Sondheim. As they headed toward opening night at Don’t Tell Mama, a Midtown piano club, the group decided that Ms. Gustern would sing three songs herself. For one of them, the “Oklahoma!” showstopper “I Cain’t Say No,” Ms. Gustern planned to pantomime sitting on the lap of a cowboy.“The thought of doing a show was like sentencing me to be tortured,” she wrote on Facebook on March 10. “But as of today all that is reversed.” Now, she continued, “I feel like a singer again for the first time in forever.”A few hours after posting those words, Ms. Gustern was shoved. She died from head injuries brought on by the fall. Ms. Pazienza, a 26-year-old former events coordinator from Queens, has been released on bail from Rikers Island and is due to appear in court on May 10.In the weeks before her death, Ms. Gustern was leading rehearsals of a cabaret show featuring Barbara Bleier, center, and Austin Pendleton, right. After a postponement, they took the stage at Don’t Tell Mama in Midtown Manhattan on March 27, with Paul Greenwood on piano.Dolly Faibyshev for The New York TimesThe “Steve and Oscar” show went on without Ms. Gustern, postponed to March 27. Before an audience of cabaret regulars seated in the banquettes of Don’t Tell Mama, Ms. Bleier and Mr. Pendleton turned the show into a tribute to their friend and director. “All these lyrics mean so many new things,” Mr. Pendleton said from the stage. He soon appeared befuddled, asking the pianist, “What am I going to sing here?”Others who relied on Ms. Gustern find themselves a little lost. The performer and writer Penny Arcade had drafted Ms. Gustern to be the musical director of a show scheduled to start around July. She said she was so shaken by Ms. Gustern’s death that she is now considering a start date in late fall. Eric Schmalenberger, a cabaret producer and performer, said he will lose what was, for a long time, the closest thing he had to an annual family tradition: trimming the Christmas tree at Ms. Gustern’s apartment with others in the music community who had nowhere else to go.But Ms. Gustern’s students have not lost her completely. She will live on for them in the form of the warm-up tapes she gave them. Many performers who studied with her said they listen to the tapes of her before every show; a few said they listen before rehearsals, too.Ms. Gustern on the carousel at St. Ann’s Warehouse in Brooklyn at a party after “Only An Octave Apart,” a 2021 show featuring Justin Vivian Bond and Anthony Ross Costanza.Joy EpisallaAmelia Zirin-Brown, a cabaret singer under the name Rizo, said that she has listened to hers more than 2,000 times. Ms. Harry and Mx. Bond estimated “thousands”; Ms. Hanna, between 500 and 1,000.They have become attached to one particular warm-up session, made specially for them. They have transferred the recordings from cassettes to CDs to computers to phones. They have backups, and backups of backups. No matter how many times they are told how to hit certain notes, or how to position their faces, they treasure the reminders.The tapes preserve the past. Mx. Bond’s includes Ms. Gustern discussing a lover from decades ago. Ms. Zirin-Brown’s assistants know the tape so well that they can predict the exact moment when, out of nowhere, Ms. Gustern’s cat jumps onto the keyboard.Ms. Gustern might have thought of herself as a helpmeet or second banana, but her students didn’t see her that way.“She meant so much more to me than I did to her, and that was totally OK,” Ms. Hanna said. “I would see her and she wouldn’t understand — I’ve been around the world with you. You’ve been here and you’ve been doing all your stuff, and, meanwhile, I’ve been in France, and you were with me. I’ve been around the world with Barbara a few times. I’m still going to be going around the world with Barbara.” More