Splitter.AI
Splitter in it's basic functionality as a Deezer Spleeter service
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Isolating instruments from music is now possible using AI, and Splitter is based on Deezer's open source research project Spleeter to accomplish this.
Could see this being a quick tool for stem separation or vocal isolation.
Edit June, 2023 - Things have changed a lot since I logged this. Nowadays I'm using djay quite often, and most of the time isolating bass, vocals, or drums just works.