I had never heard of Catru before, but I happened to find a brochure about it in the wonderful Golden Silk Boutique Hotel, whose location and staff made it our home during my Vietnam photo expedition.
Reading that Catru is a Vietnamese religious music genre, and born in the tradition of northern Vietnam, I made it an option for the participants of the expedition to attend one of its performances which are held in a restored 110 years old building (known as nha co) at 87 Ma May street in Old Hanoi. My reasoning from a practical standpoint was simple; record the performance so as to provide ambient background to the multimedia projects produced out of this trip.
Catru was already played during the 15th century during ceremonies at the Vietnamese court, but during the 1950s fell in disrepute due to its association with opium and the like.
The musician/singer in the above photograph is Ms Pham Thi Hue, a famous practitioner of this art form, who performed beautiful musical pieces during the hour-long session.
Catru Thang Long has a wonderful website, with video clips and background.