Through years of trial and error — skipping around radio streams, playing entire collections on shuffle, or repeating certain tracks over and over — we have found that the most compelling music for sustained concentration tends to contain a mixture of the following:
Noise
Drones
Arpeggios
Atmospheres
Field Recordings
Arrhythmic Textures
Vagueness (Hypnagogia)
Microtones / Dissonance
Detail / Finery / Patterns
Awesome / Daunting / Foreboding
Vast / Transcendental / Meditative