Q Light Controller+

I think it would be great if you could assign functions to precise frequencies of sound. For example if you enter the frequencies of music notes, qlcplus could let fixture flash for different notes. If you play a piano song it would look very cool I think.

That is what midi is for. Every note of your piano gives a distinct signal.
If you'd work with exact frequencies, your setup will have to be tuned in precision.
And I'm afraid that harmonics will cause uncontrollable mayhem...

IMHO it won't look that great (love to create a mood instead of flashy thingies in random colors or you like Eastern style

Thank you for your answer. I know that you can use midi to 'link' a piano to your lights, but i want to use songs from youtube.

Just a thought, and I don't know if it's really feasible, but:
Have you tried converting the file to midi format?
Download youtube as .mp3 (wav or whatever) and convert to .mid. Audacity can do this.

Maybe use midi file through QLC for lights, MP3 for sound. Syncing might be an issue.
Worth trying?

Yes, I tried that already, but thank you for thinking of a solution. Converting mp3 to midi only works if there are single notes played. I converted the song I want, but it came out very messy.

You can do this with Audio Triggers

https://www.qlcplus.org/docs/html_en_EN ... ggers.html

Thanks for adding your comment.
The OP is looking to find a solution for precise frequency analysis. So exact 261.63 Hz (C4) 293.66 Hz (D4) and so forth...