Do you mean if the song has a vocalist singing? At the Music Technology Group (https://www.upf.edu/web/mtg) we have some classifiers that do something similar there are some demos at https://replicate.com/mtg/music-classifiers, see the output of the "voice_instrumental" classifier. This is built with a dataset of examples of instrumental songs and songs with singing in them. Normally classifiers are trained on timbre of the song to identify this. Earlier versions of this classifier are also available at AcousticBrainz: https://acousticbrainz.org/

thanks for pointing me to that. avant is powered by musicbrainz actually - so I will look to see what I can pull from acousticbrainz!

I love avant.fm! Do you know about musixmatch? They have an API for time-synced lyrics and is the source of that data for a bunch of large services.

thank you!! that's very nice to hear. and I will check out musixmatch for sure.