Vocal trainer So Su-lyn, 32, stands at the forefront of where K-pop begins -- preparing young aspiring stars at her music schools in Incheon and Ilsan, Gyeonggi Province. Her goal is to equip these hopefuls with the skills they need to become trainees at major K-pop agencies and, ultimately, debut as idols.

“I’ve been working as a vocal trainer for nearly 10 years now. I teach students who want to become trainees at major companies like SM Entertainment, YG Entertainment and JYP Entertainment,” So said during an interview with The Korea Herald on Oct. 10.

So emphasizes that a positive mindset and consistency are the most important qualities required of young trainees — typically aged between 12 and 15 — to persevere in the challenging journey of becoming a K-pop idol.

There were 1,440 trainees at K-pop agencies reported to the Ministry of Culture, Sports and Tourism as of January, but only 1 percent of them will be able to debut.

“It’s a long time with short, intense training sessions in between that they have to endure. For us to continue training them, students must be determined not to give up,” So explained.

At her music school, students practice singing for two hours a day, twice a week. This is the basic class routine, but if a student is preparing for an audition, additional training sessions are scheduled.

Vocal training varies depending on the student’s needs and the audition they’re preparing for. So focuses on improving areas where they struggle, and for K-pop trainees who face monthly evaluation tests, she works to further enhance their strengths. If a performance or recording session comes up, additional lessons are conducted to prepare them.

“I guide my students to avoid using a breathy voice by having them practice scales with solid vocal fold closure, using sharp, controlled articulation through sounds like ‘k-keok’ and ‘kkook’ to help with vocal engagement," So said. "I also incorporate exercises like imitating siren sounds to improve pitch control and use lip bubbles to manage airflow while keeping the voice steady and supported.”

"K-pop singers use specific techniques to ensure their voices stay clear and rhythmic even with fast beats. The focus is on producing this sound consistently,” So added.

Diction also becomes important, as trainees learn techniques to enhance the expressiveness of the song.

“They also train to project their voices, especially in higher vocal ranges, as deeper tones are rarely used in K-pop music,” she added.

K-pop agencies look at various qualities when selecting trainees, from vocal and dance skills to natural flair. While each label prioritizes different aspects, So believes one trait is vital above all others: integrity.

“Of course, your age can't exceed 16. If you’re 18, you can’t become a trainee. After that, a trainee’s character is the most important factor. There are countless candidates who are talented and sing well. What really matters nowadays is how much this trainee can avoid causing controversy,” So said.

Apart from talent and character, finding a vocal style that matches an agency's preference is key.

For instance, YG Entertainment favors hip-hop and R&B styles while SM Entertainment prefers pop and EDM tracks with expansive, soaring sounds. JYP Entertainment, So explained, leans towards a more natural sound, even embracing imperfections as part of an authentic performance.

Maintaining a good physique is another critical factor for success.

So recalled a student who became a trainee at SM Entertainment but missed her debut because her vocal strength weakened after weight loss.

“She was set to be the main vocalist in a group about to debut, but she had to lose 4 kilograms. It’s really difficult for young kids to lose weight, but she managed to do it. However, her vocal power diminished too, and she missed the chance to join the final lineup. Eventually, she became too old to debut,” So said.

K-pop’s rigorous training and development system is something So agrees with, especially when it comes to sustaining the global K-pop phenomenon through K-pop powerhouses’ “localization” strategies.

K-pop localization strategies aim to discover talented local youngsters, put them through the K-pop training process and debut them in regional markets. By adapting this successful system to new areas, agencies hope to create regional stars who embody K-pop’s polished performance standards while appealing to local audiences.

As for the criticism that K-pop idols are being “manufactured” by their agencies, So believes that the attention to detail in K-pop performances sets the genre apart.

“K-pop emphasizes a high level of detail. While Western artists often have more freedom in their expression, K-pop idols are trained not just in performance, but in how to conduct themselves professionally. From answering questions to handling specific situations, everything is meticulously taught,” So said. “Dance moves and vocal delivery are polished to perfection, with an emphasis on even the smallest movements and enunciation. Critics may say this is K-pop’s weakness, but I see it as its strength.”

“The polished, synchronized performances and strict professionalism are what make K-pop unique,” So added.

This article is the second in a special interview series exploring the journeys of key K-pop industry professionals: a songwriter, trainer, producer and newly debuted K-pop idol. They discuss their roles, the competitive nature of the industry and the business mechanics behind K-pop’s global success. -- Ed.