This study aims to develop asynchronous formative audio feedback practices for mobile learning in higher education settings. The development was conducted in keeping with the principles of design-based research. The research activities focused on an inter-university online course, within which the use of instructor audio feedback was tested, analyzed and developed further. Participants in this study were students (n = 50) from four Finnish universities who enrolled in the 7-week course. The teaching approach of the course could best be characterized as collaborative case-based mobile learning. Furthermore, we employed a novel formative audio feedback practice that has been inspired by and follows the peer-review practices employed by scientific journals. In particular, we wanted to find out how students experienced the use of audio feedback in terms of utility, emotional support and learning. Research data was gathered through a questionnaire to the course students, transcribed audio feedback provided for the students and students' performance results. The study indicates that the novel formative audio feedback practice was successful in promoting the emotional engagement of students and personal connectivity between students and instructors. Furthermore, the audio feedback proved effective in terms of assignment revisions, and also in terms of students' self-reports of the meaning of the audio feedback for learning. The majority of students welcomed the audio feedback, and also expressed a wish for the integrated use of text and audio. Therefore, in future implementations, we will integrate the audio and written feedback.