Harmony Generator

Takes a lead vocal or monophonic melody and adds pitch-shifted harmony voices at standard diatonic intervals — major 3rd, perfect 5th, octave above, octave below, or stacks of several at once. Each harmony is generated by transposing a copy of the input by an exact semitone offset (+4, +7, +12, −12…), then mixed under the lead. Pitch shifting uses FFmpeg's rubberband filter with formant preservation when available (so harmonies sound like a different singer rather than a tape-speed trick), falling back to the asetrate resample method otherwise. Harmonies can be panned wide across the stereo field for a fuller ensemble feel. Optional loudness normalization to streaming levels.