Fabien

I listened to your Riff and from my POV it's still not the exact note for note melody and tempo of the original composition. In a matter of fact. you have not even used the chords from the original recording. What you have done is played some chords and applied a new rhythmic pattern, tempo and time signature. Don't think it’s a major copyright issue. However let's hear what others with more experience have to say.

Hi, just to understand your question more. Are you copying an excerpt from an old record and placing/splicing it into a new recording? or are you manually playing over the exact chords from another song with another instrument? If former, you would need permission if recording is not in public domain. If latter and no one can recognize or identify a similarity with an existing song, it may be able to pass. The leverage you have is that it's a chord structure you are using rather than an exact melody copied note for note. I have known composers to use a few bars from another song’s chord structure which went unnoticed. However, taking an entire song's chord structure and giving it a new melody may be quite risky.