[1] Voice + Whisper opens with "On & On", a dance number which incorporates modern rock and electronic music into its sound.

[3] "Heart" is an R&B song with a "dramatic" composition; compromising a "sentimental" piano, the track progresses with an "intense" drum beat and synthesizer.

[18][19] Voisper also made a guest appearance on labelmate Jung Dong-ha's Dream concert in Seongnam, where they performed "In Your Voice".

[21] A music video teaser for "Summer Cold" followed one week later; the full version was uploaded on June 17, where actors Jeon Yeo-been and Jang Woo-young play the onscreen couple.

[6] A promotional poster for the song showcasing Jeon was posted throughout Seoul, including in Daehangno, Hongdae, Sinchon, Nowon, and Konkuk University.

Later that day, Voisper held an album showcase at the Ilchi Art Hall in the Gangnam District of Seoul.

[2] Kim Seong-dae of MyDaily complimented Voisper's vocals, noting the group's "sweet" harmonies since its debut single "In Your Voice".

[33] Writing for TV Daily, Kim Ji-ha lauded the members' individual vocals as well as their harmony as a group.