Ayler was among the most primal of the free jazz musicians of the 1960s; critic John Litweiler wrote that "never before or since has there been such naked aggression in jazz" He possessed a deep blistering tone--achieved by using the stiff plastic Fibrecane no. 4 reeds on his tenor saxophone--and used a broad, pathos-filled vibrato.
His trio and quartet records of 1964, like Spiritual Unity and The Hilversum Session, show him advancing the improvisational notions of John Coltrane and Ornette Coleman into abstract realms where timbre, not harmony and melody, is the music's backbone. His ecstatic music of 1965 and 1966, like "Spirits Rejoice" and "Truth Is Marching In" has been compared by critics to the sound of a Salvation Army brass band, and involved simple, march-like themes which alternated with wild group improvisations and were regarded as retrieving jazz's pre-Louis Armstrong roots.
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