Music critic J. D. Considine noted "on albums, Jackson's sound isn't defined by her voice so much as by the way her voice is framed by the lush, propulsive production of Jimmy Jam and Terry Lewis." Wendy Robinson of PopMatters said "the power of Janet Jackson's voice does not lie in her pipes. She doesn't blow, she whispers ... Jackson's confectionary vocals are masterfully complemented by gentle harmonies and balanced out by pulsing rhythms, so she's never unpleasant to listen to."Matthew Perpetus of Fluxblog suggested Jackson's vocal techniques as a study for indie rock music, considering it to possess "a somewhat subliminal effect on the listener, guiding and emphasizing dynamic shifts without distracting attention from its primal hooks." Perpetus added: "Her voice effortlessly transitions from a rhythmic toughness to soulful emoting to a flirty softness without overselling any aspect of her performance ... a continuum of emotions and attitudes that add up to the impression that we're listening to the expression of a fully-formed human being with contradictions and complexities."Jackson's music has encompassed a broad range of genres. Her records from the 1980s have been described as being influenced by Prince, as her producers are ex-members of the Time. Sal Cinquemani wrote that in addition to defining Top 40 radio, she "gave Prince's Minneapolis sound a distinctly feminine—and, with songs like 'What Have You Done for Me Lately?,' 'Nasty,' 'Control,' and 'Let's Wait Awhile,' a distinctly feminist—spin."On Control, Richard J. Ripani documented that she, Jam and Lewis had "crafted a new sound that fuses the rhythmic elements of funk and disco, along with heavy doses of synthesizers, percussion, sound effects, and a rap music sensibility." Author Rickey Vincent stated that she has often been credited for redefining the standard of popular music with the industrial-strength beats of the album. She is considered a trendsetter in pop balladry, with Richard Rischar stating "the black pop ballad of the mid-1980s had been dominated by the vocal and production style that was smooth and polished, led by singers Whitney Houston, Janet Jackson, and James Ingram."Jackson continued her musical development by blending pop and urban music with elements of hip-hop in the nineties. This included a softer representation, articulated by lush, soulful ballads and up-tempo dance beats. She is described by music critic Greg Kot as "an artist who has reshaped the sound and image of rhythm and blues" within the first decade of her career. Critic Karla Peterson remarked that "she is a sharp dancer, an appealing performer, and as 'That's the Way Love Goes' proves—an ace pop-song writer." Selected material from the following decade has been viewed less favorably, as Sal Cinquemani comments "except for maybe R.E.M., no other former superstar act has been as prolific with such diminishing commercial and creative returns."Jackson has changed her lyrical focus over the years, becoming the subject of analysis in musicology, African American studies, and gender studies. David Ritz compared Jackson's musical style to Marvin Gaye's, stating, "like Marvin, autobiography seemed the sole source of her music. Her art, also like Marvin's, floated over a reservoir of secret pain." Much of her success has been attributed to "a series of powerful, metallic grooves; her chirpy, multi-tracked vocals; and a lyrical philosophy built on pride and self-knowledge." Ritz also stated, "The mystery is the low flame that burns around the perimeters of Janet Jackson's soul. The flame feeds off the most highly combustible elements: survival and ambition, caution and creativity, supreme confidence and dark fear."During the 1980s, her lyrics embodied self-actualization, feminist principles, and politically driven ideology. Gillian G. Gaar described Control as "an autobiographical tale about her life with her parents, her first marriage, and breaking free." Jessie Carney Smith wrote "with that album, she asserted her independence, individuality, and personal power. She challenged audiences to see her as a transformed person, from an ingénue to a grow-up, multi-talented celebrity." Referring to Rhythm Nation 1814 as an embodiment of hope, Timothy E. Scheurer wrote "It may remind some of Sly Stone prior to There's a Riot Going On and other African-American artists of the 1970s in its tacit assumption that the world imagined by Dr. King is still possible, that the American Dream is a dream for all people."On Janet, Jackson began focusing on sexual themes. Shayne Lee wrote that her music over the following decade "brand[ed] her as one of the most sexually stimulating vocalists of the 1990s." Lilly J. Goren observed "Jackson's evolution from politically aware musician to sexy diva marked the direction that society and the music industry were encouraging the dance-rock divas to pursue." The Washington Post declared Jackson's public image over the course of her career had shifted "from innocence to experience, inspiring such carnal albums as 1993's 'Janet' and 1997's 'The Velvet Rope', the latter of which explored the bonds—figuratively and literally—of love and lust."The song "Free Xone" from The Velvet Rope, which portrays same-sex relationships in a positive light, is described by sociologist Shayne Lee as "a rare incident in which a popular black vocalist explores romantic or sensual energy outside the contours of heteronormativity, making it a significant song in black sexual politics." During promotion for Janet, she stated "I love feeling deeply sexual—and don't mind letting the world know. For me, sex has become a celebration, a joyful part of the creative process."Upon the release of Damita Jo, Jackon stated "Beginning with the earlier albums, exploring—and liberating—my sexuality has been an ongoing discovery and theme," adding "As an artist, that's not only my passion, it's my obligation." Stephen Thomas Erlewine has found Jackson's consistent inclusion of sex in her music lacking ingenuity, especially in comparisons to other artists such as Prince, stating "while sex indisputably fuels much great pop music, it isn't an inherently fascinating topic for pop music—as with anything, it all depends on the artist."

Question: What is the last name of the person who is considered a trendsetter in pop balladry?
Answer: Jackson