MarekMarek Klein (born 1969 in Slovakia) is interested in Gregorian Chant since 1992. Besides self-study and liturgical praxis, he attended several courses and events connected with Gregorian Chant under the guidance of personalities as Jiří Hodina, David Eben, Louis-Marie Vigne, Alberto Turco, Nino Albarosa, Dom Yves-Marie Leliévre. He also participates in organisation of events of this kind.

He is the leader of the Vocal Ensemble Gregoriana of Košice, Slovakia.

In 2012, he started his Graduale Project - to which he says:

After some twenty years of my church singing career, I have decided to connect the beginning of the new liturgical year – the first advent Sunday of 2012 – with the beginning of a new project. The aim of the Graduale Project is to record all of the chants included in the current Graduale – Graduale Romanum. The recordings are published on the dedicated channel on youtube.

When singing I use Graduale Triplex (1979) and I usually pay special attention to the St. Gallen neumatic notation.

The performing of gregorian chant is different with every singer and it is impossible to consider any way of performing as the only correct one. Neither do I consider my way of singing as the only correct one or the best one. I am also aware that the chants of the graduale (the main part of them) are not meant to be sung by soloist, but by a group of singers – a schola. I hope, however, that in spite of these drawbacks, my recordings will find their audience and that they can become a helpful resource for someone – a resource, which I was looking for without success at the time of my beginnings.