The one string koto, or ichigenkin, is a very rare instrument. Masaoka has studied the ichigenkin with the 4th Iemoto of the Seikyodo Ichigenkin Tradition, Issui Minegishi. She is the great, great granddaughter of Tokuhiro Taimu, the founder of Seikyodo Ichigenkin, who was said to retreat to mountain caves in Japan to meditate, fast and play the ichigenkin for “refinement of the mind.”
The monochord is very illustrative in the the frequencies, harmonic nodes and harmonic spectrum, and the mathematical relationships and proportions of music and sound.
Masaoka also performs on various monochords, including electric monochords with various ensembles such as Hans Tammen’s Third Eye Orchestra. (link)