OFFICIAL PAGE: Photosounder
Photosounder is a unique image-based spectral editor that allows the user to transform sound into an image as well as turn an image into sound! Photosounder includes a number of spectral editing tools including a Harmonics Modifier, as well as a lossless mode for high quality results. The application is available for macOS as well as Windows, and can be run on Linux using Wine. The developer recommends running Photosounder on a powerful computer for best performance.
Screenshot courtesy of Photosounder.com