Frequency Detector Tool is a free, elegant frequency and musical-key analyzer for producers, mixing engineers, sound healers, and the musically curious. Type in any frequency in Hertz — like 315, 2.5k, or 29834 — and instantly see: The musical note it maps to (e.g. A4 = 440 Hz) How many cents sharp or flat it is Whether it's IN KEY for the key you've selected The nearest "cut candidate" — the closest out-of-key frequency Vocal context notes to guide your EQ decisions Pick your key from all 12 tones and the whole analysis updates instantly, showing the in-key snap, the nearest cut, and vocal-range context (like the "Mud Zone" around 250–400 Hz). Open the full frequency chart to see every note across octaves 0–7, laid out for boosting and cutting in your chosen key — scroll to explore the entire spectrum. Also included: Clickable Solfeggio frequencies (432, 528, 639, 741, 852, 963) with a note on what each is associated with "Did You Know?" music-theory facts A calm, sacred-geometry inspired interface Frequency Detector Tool is completely free — no ads, no subscriptions, no catch. It's my first app, made with love. If it helps you, an optional donation on eyeheru369.com supports more free tools. Works on iPhone, iPad, and Apple Vision Pro.