Stratum is a compositional genre built on the principle of perceptual stratification: a single Stratum piece contains between three and nine discrete layers of music, each accessible only to listeners with a specific level of auditory augmentation. The base layer — audible to unaugmented human ears — is typically a spare, functional piece of music: pleasant, competent, but unremarkable, often drawing on traditional acoustic instrumentation. Listeners with entry-level chrome audio augmentation perceive a second layer embedded in frequencies above human hearing, which typically recontextualizes the base layer harmonically, adding complexity and emotional depth. Each subsequent layer, accessible only with progressively more sophisticated augmentation, adds further compositional material — countermelodies, polyrhythmic percussion structures, lyrical content, and at the highest augmentation tiers, what practitioners call 'the architecture': a spatial and tonal framework that makes the entire composition cohere into something that listeners describe as overwhelming in the best possible sense. The experience of hearing a full nine-layer Stratum piece with military-grade auditory augmentation has been compared to 'standing inside a cathedral that is also a conversation.'

Stratum originated in the Circuit in the 2200s among augmented factory workers who discovered that their industrial-grade hearing augments — installed for occupational safety, not music — could perceive frequencies in recordings that others could not. Early Stratum composers were deliberately encoding hidden layers in otherwise unremarkable music, creating a private language between augmented listeners. The genre has since expanded across all tiers, though the experience varies radically: a Tier 5 listener with full-spectrum neural audio augmentation and a Shelf worker with a decade-old occupational hearing implant are technically listening to the same piece but experiencing fundamentally different compositions.