Michael, if I'm reading the information correctly, you would not use Spleeter in the way you describe. The quality is not yet adequate. I found this sentence about the purpose of the utility that speaks to how the developers think it will be used:

Purpose: We release Spleeter with pre-trained state-of-the-art models in order to help the Music Information Retrieval (MIR) community leverage the power of source separation in various MIR tasks, such as
vocal lyrics analysis from audio (audio/lyrics alignment, lyrics transcription...), music transcription (chord transcription, drums transcription, bass transcription, chord estimation, beat tracking), singer identification,
any type of multi-label classification (mood/genre...) or vocal melody extraction.

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