sbr-crystalizer.js demo
Pick a low-quality voice recording (or use the built-in synthetic one), press Crystalize, then compare. Everything runs in your browser; nothing is uploaded.
No audio loaded.
Original
Spectrogram, 0 to Nyquist, bright = louder.
ProcessedThis is a perceptual enhancer: it adds a plausible top end, it cannot recover information the recording has lost. Read the README.