For a number of stars, becoming a great singer took a lot of hard work and improvement over the years. Veteran K-Pop vocal coaches Kim Young Min and Lee Gyeol recently sat down with AYO on YouTube to reveal which boy group idols they think have made the most “remarkable” leap in singing skills since their trainee days.

1. Minhyun (NU’EST)

Kim Young Min has trained numerous idols over the past 11 years, including members of SEVENTEEN, NU’EST, IZ*ONE, and fromis_9.

The first idol he named who’s improved remarkably over the years is NU’EST’s Minhyun. The group’s visual, Minhyun was first scouted by Pledis Entertainment on his way home from school. However, despite initially being cast for his looks, he’s gone on to become the lead vocalist of both NU’EST and former Produce group Wanna One.

Minhyun is very hard working, always goes to gym, and practices regularly.

— Kim Young Min

Many fans have described his voice as angelic and underrated, especially when he sings in a higher key. According to Kim Young Min, Minhyun’s skill is all down to his diligence and consistent hard work over the years.

It’s not easy at all. I think it’s awesome that he’s been through such a hard time and still practices steadily.

— Kim Young Min

2. Dino (SEVENTEEN)

The second idol Kim Young Min praised is SEVENTEEN’s Dino. In fact, the vocal coach said that Dino’s improvements are so impressive, he even looks up to the idol himself.

He was the first idol who I thought I wanted to emulate.

— Kim Young Min

Dino was cast by Pledis Entertainment at a dance competition when he was just 12 years old. Despite being cast as a dancer, he worked hard to become a sub vocalist (also known as vocalist) in the group, particularly excelling at low to mid-range notes.

He knew that his singing skills were lacking but he didn’t give up. His singing improved a lot, and now he sings some parts too.

— Kim Young Min

3. Cha Eunwoo (ASTRO)

Lee Gyeol has been a vocal trainer for 17 years, working with Click B, SISTAR, Cosmic Girls, and Weki Meki among others.

The first idol on his list of singing improvements is ASTRO‘s Cha Eunwoo. The group’s visual, Eunwoo was scouted at his school fair, but soon went on to become part of ASTRO’s vocal line.

He tries so~ hard. When he first debuted, he wasn’t in the center. One day, I was watching TV [and said] ‘Eunwoo is the center?!’, ‘He sings a lot too!’.

— Lee Gyeol

Lee Gyeol says Cha Eunwoo worked very hard to get to where he is now. The result is a smooth, smokey tone and a particular skill at using his lower register.

[To Cha Eunwoo] Your singing has improved! So nice!

— Lee Gyeol

4. Rocky (ASTRO)

Finally, the last idol Lee Gyeol named is fellow ASTRO member Rocky. Rocky may be ASTRO’s main dancer, but Lee Gyeol revealed he’s always working harder to become an even more impressive singer.

This guy… is hard! Too passionate! Keeps calling me saying, ‘Please check out my singing’!

— Lee Gyeol

Lee told viewers that Rocky is so passionate about improving, he often calls asking the trainer to review his practice efforts. Despite his bad boy rapper vibe, he has a truly angelic vocal tone.

He sent me a song he recorded not long ago, and I downloaded it but hadn’t played it yet. One day, I was listening to a song thinking ‘this is Bruno Mars’, and it was Rocky! I was so surprised! Now you’re ‘Bruno Rocky’.

— Lee Gyeol