At the age of 25, Yokoyama began to study with Fukuda Rando, founder of the Azuma School and with Watazumi Doso, a legendary Fuke master who sought to synthesize shakuhachi music and spirituality within the context of Zen Buddhism.
Guided by these two eminent masters, Yokoyama was able to combine the modernism of Rando with the deeply religious traditional spirit of Watazumido in his training.
A descendant of the Kinko tradition transmitted down through the generations, he also pioneered a revolution in modern music that swept across post-War Japan.
Yokoyama achieved international attention for his New York City premiere performance in November 1967, of Tōru Takemitsu's composition November Steps, for shakuhachi, biwa, and orchestra, with the New York Philharmonic, under the direction of Seiji Ozawa (with biwa player Tsuruta Kinshi).
At this gathering, five of the world's greatest shakuhachi masters, including Yokoyama, performed in a single venue for the first time ever.