Harmonic filter

The idea came to me when thinking about simulating drum resonance.

For kicks and snares I use a standard resonant HP filter for that - I cut off unwanted low-end and boost the drum body resonance, giving more thump to the drum sound.

However - I realized that the resonance is not just one band - it should be a series of bands creating a harmonic series. But that's not esy to do with simple peak filters - you'd need to stack them, and calculate frequencies and gains for good simulation, and changing the frequency would require a ton of manual work.

Why not make a special filter unit that creates a harmonic (or inharmonic if the user wants) bank of bell (peak) filters that tune automatically to harmonic frequencies of the fundamental filter frequency picked by user? This could be also a harmonic notch filter as well - creating comb-like efects but in a different and much more controlable fashion -because one could for example change the harmonic to inharmonic with automation.

Just an idea. What do you think?

No files, tests, or entry points are identified in the issue. Start by locating LMMS's existing resonant, peak, and notch filter units, then clarify the filter's harmonic and inharmonic behavior, controls, and acceptance criteria before implementation.

Written by the indexing model from the issue text.