Good questions. I'll go through them one by one.
No AI: It means no black-box ML model deciding what you hear. The engine is data-driven. It uses structured signals from a proprietary database, but the logic is deterministic and inspectable, not a trained model. "No AI" also refers to the music itself: no AI-generated tracks, no synthetic filler.
The 90% Vault swing: Fair challenge. Two runs pull from a deliberately large qualifying pool, then vary the sampling. So you get a different valid slice each time, not noise. The pool is constrained by relevance filters. The shuffle is intentional so repeat runs stay fresh rather than identical. You're right that a 90% swing sits on the edge between intentional variety and low-precision pool. I'm not going to overclaim coherence here. It's tuned to lean toward variety because the whole point is hearing something different every time. If convergence is something users want, it's a knob I could expose.
Essential/Balanced/Adventurous: Based on catalog-relationship distance, not audio features. How far the recommendation sits from the seed across the signals the engine uses. You're right that adjacency can feel adventurous without being so. Honest answer: it's validated by listening and user feedback, not a published metric. 350+ paying users and growing, and the depth levels are the feature I get the most positive feedback on, especially Adventurous. But no, there's no formal benchmark behind it.
Ghost artists and AI tracks: Legitimate concern, and you're right that deep cuts are exactly where synthetic content hides. I run my own verification process rather than trusting what the platforms filter out. It's active and ongoing, not a one-time claim. Not perfect yet, but it's mine, not theirs.
API dependency: Straight answer. No, I don't have direct commercial deals with Tidal or Qobuz like Roon does. It's a real dependency risk. Contingency is multi-platform support. Already live on Tidal and Qobuz, YouTube Music coming soon. No single platform is a point of failure. And the selection logic is platform-independent. It doesn't rely on their recommendation APIs, only library access and playback.
Give it a try. Pick an artist you know well, set it to Adventurous, and see if the mechanism holds up for you. I think it will.
Alessandro

