Windows audio upscaler: transparent 192kHz/32-bit conversion plus HF reconstruction (C++/Qt6, GPLv3)
Here is how upsampling usually goes. You pay for a program, or a plugin, or a plugin that hosts other plugins. You feed it a 48 kHz file. It hands back a 384 kHz file roughly eight times the size, and a forum thread assures you it sounds "more analog." Nobody shows you a spectrum. Nobody shows you a single sample. You are expected to take it on faith, and when you ask what actually changed, someone tells you to buy better cables.
Ultraviolet is the opposite of that. It converts audio to 88.2 through 384 kHz, in 32-bit or 64-bit float, and when the source has had its top end chopped off by a codec or a lazy master, it builds a high-frequency extension that picks up where the music stopped. Then it shows you exactly what it did: the spectrum, the spectrograms, the individual samples, and an audition of nothing but the added content so you can decide for yourself whether you like it.
Nothing is written to disk until you say so.
The full documentation is in the README.
Ultraviolet upscales audio files to high sample rates and bit depths. It does two separable jobs and is honest about the difference:
1. Transparent conversion. A reference-grade arbitrary-ratio resampler and noise-shaped requantization take a source (e.g. 48 kHz / 16-bit) to 192 kHz / 32-bit without altering the original passband. Provably lossless in-band. 2. High-frequency reconstruction. For sources whose top end was rolled off (lossy codecs, older recordings), Ultraviolet synthesizes plausible content in the 10-20 kHz region, and optionally adds ultrasonic character. This is resynthesis, not recovery: nothing restores information a brickwall filter removed from a true full-band capture.
Mode is user-selectable (Mastering / Rescue / Auto), with Auto deciding per source from a measured high-frequency rolloff.